Patent Publication Number: US-2021186114-A1

Title: Method for controlling temperature of heater and aerosol generating device performing same method

Description:
TECHNICAL FIELD 
     The present disclosure relates to a control method of compensating for a temperature of a heater and an aerosol generator executing the method. 
     BACKGROUND ART 
     Recently, there has been increasing demand for alternative ways of overcoming the disadvantages of common cigarettes. For example, demand has been increasing for a method of generating aerosol by heating an aerosol generating material in a cigarette, not a method of generating aerosol by burning the cigarette. Accordingly, research into a heating-type cigarette and a heating-type aerosol generator has been actively conducted. 
     Also, research into a method of controlling a temperature of a heater that heats a cigarette accommodated in an aerosol generator has been conducted. In particular, a control method for maintaining a temperature of a heater at a certain temperature has been developed to provide a user with aerosol of uniform amount from an aerosol generator. 
     In order for the aerosol generator to provide the user with the aerosol, it is demanded to maintain the temperature of the heater at a certain temperature or higher, and thus, the user has to standby before smoking using the aerosol generator. Therefore, a technique for increasing the temperature of the heater to a certain temperature or higher within a short period of time and maintaining the temperature of the heater at the certain temperature is necessary. 
     Also, since the temperature of the heater has to be decreased in order to maintain the temperature of the heater at a proper level after the heater has been heated to a high temperature within a short period of time, the temperature of the heater tends to fall below the certain temperature as the smoking is proceeded, and accordingly, degradation in smoking quality occurs. Therefore, a technique for preventing degradation of smoking quality is necessary. 
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Technical Problem 
     One or more exemplary embodiments provide a method of controlling a temperature of a heater and an aerosol generator executing the method. However, the technical goal of the present disclosure is not limited thereto, and other technical goals may be inferred from the following exemplary embodiments. 
     Solution to Problem 
     According to an aspect of the disclosure, there is provided an aerosol generator including a heater for heating a cigarette accommodated in the aerosol generator, a battery for supplying electric power to the heater, and a controller for controlling the electric power supplied to the heater to increase a temperature of the heater to a reference temperature or greater, the reference temperature being set to be suitable for generating aerosol from a cigarette, and setting a target temperature of the heater and controlling the electric power supplied to the heater to maintain the temperature of the heater at the reference temperature, wherein the controller adjusts the target temperature in order to compensate for the temperature of the heater, which decreases below the reference temperature. 
     According to another aspect of the disclosure, there is provided a method of controlling a temperature of a heater for heating a cigarette accommodated in an aerosol generator, the method including controlling an electric power supplied to the heater to increase a temperature of the heater to a reference temperature or greater, the reference temperature being set to be suitable for generating aerosol from the cigarette, and setting a target temperature of the heater and controlling the electric power supplied to the heater to maintain the temperature of the heater at the reference temperature, wherein the controlling of the electric power supplied to the heater to maintain at the reference temperature includes adjusting the target temperature in order to compensate for the temperature of the heater, which decreases below the reference temperature. 
     Advantageous Effects of Disclosure 
     According to a method of controlling a temperature of a heater of the disclosure, a time taken to prepare an aerosol generator for providing a user with aerosol may be reduced because the heater may be heated to a reference temperature or greater within a short period of time, and accordingly, the user may be provided with a sufficient amount of aerosol from an initial stage of smoking. 
     Also, because the temperature of the heater is controlled to be decreased as the heater is heated to the reference temperature or greater within an excessively short period of time, reduction in the temperature of the heater decreases below the reference temperature as the smoking has proceeded may be prevented. Therefore, even if the smoking lasts longer, the temperature of the heater may be maintained at a reference temperature and aerosol may be provided uniformly from the aerosol generator. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIGS. 1 to 3  are diagrams showing examples in which a cigarette is inserted into an aerosol generator. 
         FIG. 4  illustrates an example of a cigarette. 
         FIG. 5  is a block diagram of an example of an aerosol generator according to an exemplary embodiment of the disclosure. 
         FIG. 6  is a graph illustrating a method of controlling a temperature of a heater in an aerosol generator according to sections. 
         FIG. 7  is a flowchart illustrating an example of a method of controlling electric power supplied to a heater according to an exemplary embodiment of the disclosure. 
         FIG. 8  is a flowchart illustrating an example of a method of controlling electric power supplied to a heater according to another exemplary embodiment of the disclosure. 
         FIG. 9  is a flowchart illustrating an example of a method of controlling electric power supplied to a heater according to another exemplary embodiment of the disclosure. 
         FIG. 10  is a graph illustrating a method of controlling a temperature of a heater in an aerosol generator according to sections. 
         FIG. 11  is a flowchart illustrating an example of a method of controlling a temperature of a heater in an aerosol generator according to sections, according to an exemplary embodiment of the disclosure. 
         FIG. 12  is a flowchart illustrating an example, in which a controller determines a period of a temperature reduction section. 
         FIG. 13  is a flowchart illustrating an example, in which a controller determines a period of a temperature retaining section. 
         FIG. 14  is a graph for describing differences of the method of controlling the temperature of the heater differently in the pre-heating section and the maintaining section from the method of controlling the temperature without dividing the sections according to the related art, and issues of the method of controlling the temperature for each section. 
         FIG. 15  is a graph illustrating an example of adjusting a target temperature according to one or more exemplary embodiments of the disclosure. 
         FIG. 16  is a graph illustrating another example of adjusting a target temperature according to one or more exemplary embodiments of the disclosure. 
         FIG. 17  is a graph illustrating an accumulated value obtained by accumulating a difference value between a temperature of a heater and a target temperature according to time, according to one or more exemplary embodiments of the disclosure. 
         FIG. 18  is a graph illustrating an example of adjusting a target temperature based on a variation in an accumulated value, according to one or more exemplary embodiments of the disclosure. 
         FIG. 19  is a graph illustrating another example of adjusting a target temperature based on a variation in an accumulated value, according to one or more exemplary embodiments of the disclosure. 
         FIG. 20  is a flowchart illustrating a method of controlling a temperature of a heater for heating a cigarette accommodated in the aerosol generator according to one or more exemplary embodiments of the disclosure. 
     
    
    
     BEST MODE 
     According to an aspect of the disclosure, there is provided an aerosol generator including a heater for heating a cigarette accommodated in the aerosol generator; a battery for supplying electric power to the heater; and a controller configured to: control the electric power supplied to the heater to increase a temperature of the heater to a reference temperature or greater, the reference temperature being set to be suitable for generating aerosol from the cigarette, set a target temperature of the heater, control the electric power supplied to the heater based on the target temperature such that the temperature of the heater is maintained at the reference temperature, and adjust the target temperature to compensate for the temperature of the heater when the temperature of the heater decreases below the reference temperature. 
     The controller may adjust the target temperature based on an accumulated value obtained by accumulating a difference value between the temperature of the heater and the target temperature with lapse of time. 
     The controller may adjust the target temperature based on a decreasing degree of the accumulated value from a maximum value of the accumulated value. 
     The controller may adjust the target temperature by adding a decreased value to an initial value, the decreased value being obtained by multiplying the decreasing degree of the accumulated value from the maximum value by a constant. 
     The controller may discontinuously adjust the target temperature. 
     The controller may adjust the target temperature by changing the target temperature once. 
     The controller may adjust the target temperature by linearly changing the target temperature. 
     The controller may set the target temperature at a time point when the temperature of the heater becomes higher than the reference temperature. 
     The controller may adjust the target temperature at a time point when the temperature of the heater decreases below the reference temperature. 
     The controller may set the target temperature to be equal to the reference temperature. 
     The controller may control the electric power supplied to the heater by adjusting at least one of a frequency and a duty cycle of a current pulse supplied by the battery to the heater. 
     The reference temperature may be between 240° C. and 360° C. 
     According to another aspect of the disclosure, there is provided a method of controlling electric power supplied to the heater to increase a temperature of the heater to a reference temperature or greater, the reference temperature being set to be suitable for generating aerosol from the cigarette; setting a target temperature of the heater; controlling the electric power supplied to the heater based on the target temperature such that the temperature of the heater is maintained at the reference temperature; and adjusting the target temperature to compensate for the temperature of the heater when the temperature of the heater decreases below the reference temperature. 
     According to another aspect of the disclosure, there is provided a computer-readable recording medium having recorded thereon a program for performing on a computer a method of controlling a temperature of a heater for heating a cigarette accommodated in an aerosol generator, wherein the method includes controlling electric power supplied to the heater to increase a temperature of the heater to a reference temperature or greater, the reference temperature being set to be suitable for generating aerosol from the cigarette; setting a target temperature of the heater; controlling the electric power supplied to the heater based on the target temperature such that the temperature of the heater is maintained at the reference temperature; and adjusting the target temperature to compensate for the temperature of the heater when the temperature of the heater decreases below the reference temperature. 
     MODE OF DISCLOSURE 
     As the present disclosure allows for various changes and numerous exemplary embodiments, particular exemplary embodiments will be illustrated in the drawings and described in detail in the written description. The attached drawings for illustrating one or more exemplary embodiments are referred to in order to gain a sufficient understanding, the merits thereof, and the objectives accomplished by the implementation. However, the exemplary embodiments may have different forms and should not be construed as being limited to the descriptions set forth herein. 
     The example exemplary embodiments will be described below in more detail with reference to the accompanying drawings. Those components that are the same or are in correspondence are rendered the same reference numeral regardless of the figure number, and redundant explanations are omitted. 
     While such terms as “first,” “second,” etc., may be used to describe various components, such components are not be limited to the above terms. The above terms are used only to distinguish one component from another. 
     An expression used in the singular encompasses the expression of the plural, unless it has a clearly different meaning in the context. 
     In the present specification, it is to be understood that the terms “including,” “having,” and “comprising” are intended to indicate the existence of the features, numbers, steps, actions, components, parts, or combinations thereof disclosed in the specification, and are not intended to preclude the possibility that one or more other features, numbers, steps, actions, components, parts, or combinations thereof may exist or may be added. 
     When a certain exemplary embodiment may be implemented differently, a specific process order may be performed differently from the described order. For example, two consecutively described processes may be performed substantially at the same time or performed in an order opposite to the described order. 
     Hereinafter, exemplary embodiments of the present disclosure will be described in detail with reference to the drawings. 
       FIGS. 1 to 3  are diagrams showing examples in which a cigarette is inserted into an aerosol generator. 
     Referring to  FIG. 1 , an aerosol generator  10  includes a battery  120 , a controller  110 , and a heater  130 . Referring to  FIG. 2  and  FIG. 3 , the aerosol generator  10  further includes a vaporizer  180 . Also, a cigarette  200  may be inserted into an inner space of the aerosol generator  10 . 
       FIGS. 1 to 3  show some elements particularly related to the aerosol generator  10  according to the exemplary embodiments. Therefore, one of ordinary skill in the art would appreciate that other elements than the elements shown in  FIGS. 1 to 3  may be further included in the aerosol generator  10 . 
     Also,  FIGS. 2 and 3  show that the aerosol generator  10  includes the heater  130 , but if necessary, the heater  130  may be omitted. 
     In  FIG. 1 , the battery  120 , the controller  110 , and the heater  130  are arranged in serial. Also,  FIG. 2  shows that the battery  120 , the controller  110 , the vaporizer  180 , and the heater  130  are arranged in serial. Also,  FIG. 3  shows that the vaporizer  180  and the heater  130  are arranged in parallel. However, an internal structure of the aerosol generator  10  is not limited to the examples shown in  FIGS. 1 to 3 . That is, according to a design of the aerosol generator  10 , the arrangement of the battery  120 , the controller  110 , the heater  130 , and the vaporizer  180  may be changed. 
     When the cigarette  200  is inserted into the aerosol generator  10 , the aerosol generator  10  operates the heater  130  and/or the vaporizer  180  to generate aerosol from the cigarette  200  and/or the vaporizer  180 . The aerosol generated by the heater  130  and/or the vaporizer  180  may be transferred to a user via the cigarette  200 . 
     As necessary, even when the cigarette  200  is not inserted in the aerosol generator  10 , the aerosol generator  10  may heat the heater  130 . 
     The battery  120  supplies the electric power used to operate the aerosol generator  10 . For example, the battery  120  may supply power for heating the heater  130  or the vaporizer  180  and supply power for operating the controller  110 . In addition, the battery  120  may supply power for operating a display, a sensor, a motor, and the like installed in the aerosol generator  10 . 
     The controller  120  controls the overall operation of the aerosol generator  10 . In detail, the controller  110  may control operations of other elements included in the aerosol generator  10 , as well as the battery  120 , the heater  130 , and the vaporizer  180 . Also, the controller  110  may check the status of each component in the aerosol generator  10  to determine whether the aerosol generator  10  is in an operable state. 
     The controller  110  includes at least one processor. A processor can be implemented as an array of a plurality of logic gates or can be implemented as a combination of a general-purpose microprocessor and a memory in which a program executable in the microprocessor is stored. It will be understood by one of ordinary skill in the art that the present disclosure may be implemented in other forms of hardware. 
     The heater  130  may be heated by the electric power supplied from the battery  120 . For example, when the cigarette  200  is inserted in the aerosol generator  10 , the heater  130  may be located outside the cigarette  200 . Therefore, the heated heater  130  may raise the temperature of an aerosol generating material in the cigarette  200 . 
     The heater  130  may be an electro-resistive heater. For example, the heater  130  includes an electrically conductive track, and the heater  130  may be heated as a current flows through the electrically conductive track. However, the heater  130  is not limited to the above example, and any type of heater may be used provided that the heater is capable of being heated to a desired temperature. Here, the desired temperature may be set in advance on the aerosol generator  10 , or may be set by a user. 
     In addition, in another example, the heater  130  may include an induction heating-type heater. In detail, the heater  130  may include an electrically conductive coil for heating the cigarette  200  in an induction heating method, and the cigarette may include a susceptor that may be heated by the induction heating-type heater. 
     For example, the heater may include a tubular-type heating element, a plate-type heating element, a needle-type heating element, or a rod-type heating element, and may heat the inside or outside of the cigarette  200  according to the shape of the heating element. 
     Also, there may be a plurality of heaters  130  in the aerosol generator  10 . Here, the plurality of heaters  130  may be arranged to be inserted into the cigarette  200  or on the outside of the cigarette  200 . Also, some of the plurality of heaters  130  may be arranged to be inserted into the cigarette  200  and the other may be arranged on the outside of the cigarette  200 . In addition, the shape of the heater  130  is not limited to the example shown in  FIGS. 1 to 3 , but may be manufactured in various shapes. 
     The vaporizer  180  may generate aerosol by heating a liquid composition, and the generated aerosol may be delivered to the user after passing through the cigarette  200 . In other words, the aerosol generated by the vaporizer  180  may move along an air flow passage of the aerosol generator  10 , and the air flow passage may be configured for the aerosol generated by the vaporizer  180  to be delivered to the user through the cigarette  200 . 
     For example, the vaporizer  180  may include a liquid storage unit, a liquid delivering unit, and a heating element, but is not limited thereto. For example, the liquid storage unit, the liquid delivering unit, and the heating element may be included in the aerosol generator  10  as independent modules. 
     The liquid storage may store a liquid composition. For example, the liquid composition may be a liquid including a tobacco-containing material including a volatile tobacco flavor component, or a liquid including a non-tobacco material. The liquid storage unit may be detachable from the vaporizer  180  or may be integrally manufactured with the vaporizer  180 . 
     For example, the liquid composition may include water, solvents, ethanol, plant extracts, flavorings, flavoring agents, or vitamin mixtures. The flavoring may include, but is not limited to, menthol, peppermint, spearmint oil, various fruit flavoring ingredients, etc. The flavoring agent may include components that may provide the user with various flavors or tastes. Vitamin mixtures may be a mixture of at least one of vitamin A, vitamin B, vitamin C, and vitamin E, but are not limited thereto. Also, the liquid composition may include an aerosol former such as glycerin and propylene glycol. 
     The liquid delivery element may deliver the liquid composition of the liquid storage to the heating element. For example, the liquid delivery element may be a wick such as cotton fiber, ceramic fiber, glass fiber, or porous ceramic, but is not limited thereto. 
     The heating element is a means for heating the liquid composition delivered by the liquid delivering unit. For example, the heating element may be a metal heating wire, a metal hot plate, a ceramic heater, or the like, but is not limited thereto. In addition, the heating element may include a conductive filament such as nichrome wire and may be wound around the liquid delivery element. The heating element may be heated by a current supply and may transfer heat to the liquid composition in contact with the heating element, thereby heating the liquid composition. As a result, aerosol may be generated. 
     For example, the vaporizer  180  may be referred to as a cartomizer or an atomizer, but is not limited thereto. 
     In addition, the aerosol generator  10  may further include universal elements, in addition to the battery  120 , the controller  110 , the heater  130 , and the vaporizer  180 . For example, the aerosol generator  10  may include a display capable of outputting visual information and/or a motor for outputting tactile information. In addition, the aerosol generator  10  may include at least one sensor (a puff sensor, a temperature sensor, a cigarette insertion sensor, etc.) Also, the aerosol generator  10  may be manufactured to have a structure, in which external air may be introduced or internal air may be discharged even in a state where the cigarette  200  is inserted. 
     Although not shown in  FIGS. 1 to 3 , the aerosol generator  10  may configure a system with an additional cradle. For example, the cradle may be used to charge the battery  120  of the aerosol generator  10 . Alternatively, the heater  130  may be heated while the cradle and the aerosol generator  10  are coupled to each other. 
     The cigarette  200  may be similar to a regular combustion-type cigarette. For example, the cigarette  200  may include a first portion containing an aerosol generating material and a second portion including a filter and the like. The second portion of the cigarette  200  may also include the aerosol generating material. For example, an aerosol generating material made in the form of granules or capsules may be inserted into the second portion. 
     The entire first portion may be inserted into the aerosol generator  10 , and the second portion may be exposed to the outside. Alternatively, only a portion of the first portion may be inserted into the aerosol generator  10 . Otherwise, the entire first portion and a portion of the second portion may be inserted into the aerosol generator  10 . The user may inhale aerosol while holding the second portion by the mouth of the user. At this time, the aerosol is generated as the outside air passes through the first portion, and the generated aerosol passes through the second portion and is delivered to a user&#39;s mouth. 
     For example, the outside air may be introduced through at least one air passage formed in the aerosol generator  10 . For example, opening and closing of the air passage formed in the aerosol generator  10  and/or the size of the air passage may be adjusted by a user. Accordingly, the amount and smoothness of smoke may be adjusted by the user. In another example, the outside air may be introduced into the cigarette  200  through at least one hole formed in a surface of the cigarette  200 . 
     Hereinafter, an example of the cigarette  200  will be described with reference to  FIG. 4 . 
       FIG. 4  illustrates an example of a cigarette. 
     Referring to  FIG. 4 , the cigarette  200  includes a tobacco rod  210  and a filter rod  220 . The first portion described above with reference to  FIGS. 1 to 3  may include the tobacco rod  210  and the second portion may include the filter rod  220 . 
     In  FIG. 4 , the filter rod  220  is shown as a single segment, but is not limited thereto. In other words, the filter rod  220  may include a plurality of segments. For example, the filter rod  220  may include a first segment for cooling down the aerosol and a second segment for filtering a predetermined component included in the aerosol. Also, if necessary, the filter rod  220  may further include at least one segment performing other functions. 
     The cigarette  200  may be packaged by at least one wrapper  240 . The wrapper  240  may include at least one hole through which the outside air is introduced or inside air is discharged. For example, the cigarette  200  may be packaged by one wrapper  240 . In another example, the cigarette  200  may be packaged by two or more wrappers  240 . For example, the tobacco rod  210  may be packaged by a first wrapper and the filter rod  220  may be packaged by a second wrapper. In addition, the tobacco rod  210  and the filter  220  are respectively packaged by single wrappers, and then, the cigarette  200  may be entirely re-packaged by a third wrapper. When each of the tobacco rod  210  and the filter rod  220  includes a plurality of segments, each of the segments may be packaged by a single wrapper, and the segments of the cigarette  200  may be re-packaged by another wrapper. 
     The tobacco rod  210  includes an aerosol generating material. For example, the aerosol generating material may include at least one of glycerin, propylene glycol, ethylene glycol, dipropylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, and oleyl alcohol, but it is not limited thereto. In addition, the tobacco rod  210  may include other additive materials like a flavoring agent, a wetting agent, and/or an organic acid. Also, a flavoring liquid such as menthol, humectant, etc. may be added to the tobacco rod  210  by being sprayed to the tobacco rod  210 . 
     The tobacco rod  210  may be manufactured variously. For example, the tobacco rod  210  may be fabricated as a sheet or a strand. Also, the tobacco rod  210  may be fabricated by tobacco leaves that are obtained by fine-cutting a tobacco sheet. Also, the tobacco rod  210  may be surrounded by a heat conducting material. For example, the heat-conducting material may be, but is not limited to, a metal foil such as aluminum foil. For example, the heat conducting material surrounding the tobacco rod  210  may improve a thermal conductivity applied to the tobacco rod by evenly dispersing the heat transferred to the tobacco rod  210 , and thus, improving tobacco taste. Also, the heat conducting material surrounding the tobacco rod  210  may function as a susceptor that is heated by an inducting heating-type heater. Although not shown in the drawings, the tobacco rod  210  may further include a susceptor, in addition to the heat conducting material surrounding the outside thereof. 
     The filter rod  220  may be a cellulose acetate filter. In addition, the filter rod  220  is not limited to a particular shape. For example, the filter rod  220  may be a cylinder-type rod or a tube-type rod including a cavity therein. Also, the filter rod  220  may be a recess type rod. When the filter rod  220  includes a plurality of segments, at least one of the plurality of segments may have a different shape from the others. 
     The filter rod  220  may be manufactured to generate flavor. For example, a flavoring liquid may be sprayed to the filter rod  220  or separate fibers on which the flavoring liquid is applied may be inserted in the filter rod  220 . 
     Also, the filter rod  220  may include at least one capsule  230 . Here, the capsule  230  may generate flavor or may generate aerosol. For example, the capsule  230  may have a structure that a liquid containing a flavoring material is wrapped with a film. The capsule  230  may have a circular or cylindrical shape, but is not limited thereto. 
     When the filter rod  220  includes a segment for cooling down the aerosol, the cooling segment may include a polymer material or a biodegradable polymer material. For example, the cooling segment may include pure polylactic acid alone, but the material for forming the cooling segment is not limited thereto. In some exemplary embodiments, the cooling segment may include a cellulose acetate filter having a plurality of holes. However, the cooling segment is not limited to the above examples, and may include any material that is capable of cooling down the aerosol. 
     Although not shown in  FIG. 4 , the cigarette  200  according to the exemplary embodiment may further include a front-end filter. The front-end filter may be positioned at a side of the tobacco rod  210 , the side not facing the filter rod  220 . The front-end filter may prevent the tobacco rod  210  from escaping to the outside and may prevent the liquefied aerosol from flowing to the aerosol generator  10  (see  FIGS. 1 to 3 ) from the tobacco rod  210  during smoking. 
       FIG. 5  is a block diagram of an example of an aerosol generator according to an exemplary embodiment of the disclosure. 
     Referring to  FIG. 5 , the aerosol generator  10  according to the exemplary embodiment includes the controller  110 , the battery  120 , the heater  130 , a pulse-width modulation processor  140 , a display  150 , a motor  160 , and a storage device  170 . 
     The controller  110  controls overall operations of the battery  120 , the heater  130 , the pulse-width modulation processor  140 , the display  150 , the motor  160 , and the storage device  170  included in the aerosol generator  10 . Although not shown in  FIG. 5 , in some exemplary embodiments, the controller  110  may further include an input receiver (not shown) for receiving a button input or a touch input from a user and a communicator (not shown) that may communicate with an external communication device such as a user terminal. Although not shown in  FIG. 5 , the controller  110  may further include a module for performing proportional integral difference (PID) control on the heater  130 . 
     The battery  120  supplies electric power to the heater  130 , and the magnitude of the electric power supplied to the heater  130  may be adjusted by the controller  110 . 
     The heater  130  generates heat due to specific resistance when receiving the electric power. When an aerosol generating material is in contact with (coupled to) the heated heater, the aerosol may be generated. 
     The pulse-width modulation processor  140  may allow the controller  110  to control the electric power supplied to the heater  130  by transferring a pulse-width modulation (PWM) signal to the heater  130 . In some exemplary embodiments, the pulse-width modulation processor  140  may be included in the controller  110 . 
     The display  150  visually outputs various alarm messages of the aerosol generator  10  to allow the user of the aerosol generator  10  to check the messages. The user may check a low-battery message, an overheat alarm message of the heater, etc. output on the display  150 , and may take measures before the aerosol generator  10  stops operating or is damaged. 
     The motor  160  is driven by the controller  110  and allows the user to recognize that the aerosol generator  10  is ready for use through a tactile response. 
     The storage device  170  may store various information by which the controller  110  appropriately controls the electric power supplied to the heater  130  and various flavors are provided to the user of the aerosol generator  10 . For example, a first method or a second method that will be described later may be one of methods for controlling the electric power supplied to the heater  130  by the controller  110 , and may be stored in the storage device  170  and then transferred to the controller  110  by fetch of the controller  110 . In another example, the information stored in the storage device  170  may include a temperature profile that is referred to by the controller  110  for controlling the temperature of the heater to be appropriately reduced or increased over time, a controller reserve ratio that will be described later, a comparing control value, etc., and the information may be sent to the controller  110  according to a request from the controller  110 . The storage device  170  may include a non-volatile memory such as a flash memory, or may include a volatile memory that temporarily stores data only while being electrically conducted in order to ensure fast data input/output (I/O) speed. 
     The method for the controller  110  to control the electric power supplied to the heater  130  according to the exemplary embodiment will be described later with reference to  FIG. 6  for convenience of description. 
       FIG. 6  is a graph illustrating a method of controlling a temperature of a heater in an aerosol generator according to sections. 
     Referring to  FIG. 6 , the graph includes boundary lines  610   a  and  610   b  representing a pre-heating temperature section, a temperature variation curve  630  of a heater according to a PWM method according to the related art, a temperature variation curve  650  of the heater according to the PID method according to the related art, and a temperature variation curve  670  of the heater according to an exemplary embodiment of the present invention. In  FIG. 6 , the transverse axis denotes time in seconds and the longitudinal axis denotes Celsius temperature. 
     The boundary lines  610   a  and  610   b  representing the pre-heating temperature section respectively denote a lower limit and an upper limit of the pre-heating temperature section according to an exemplary embodiment. Referring to  FIG. 6 , the lower limit of the pre-heating temperature section is 190° C. and the upper limit of the pre-heating temperature section is 280° C. Since the temperatures 190° C. and 280° C. are exemplary numerical values according to the exemplary embodiment of the disclosure, the lower limit and the upper limit of the pre-heating temperature section may vary depending on exemplary embodiments. For example, the lower limit of the pre-heating temperature section is selected from a range of 160° C. to 220° C. and the upper limit of the pre-heating temperature section may be selected from a range of 250° C. to 310° C. 
     According to the temperature variation curve  630  of the heater according to the PWM method of the related art, the temperature of the heater rapidly rises to about 390° C. after 7 or 8 seconds later, and slowly decreases. When the electric power is supplied to the heater with a fixed PWM, an overshoot may occur after the temperature of the heater reaches the target temperature. 
     In addition, according to the temperature variation curve  650  of the heater according to the PID method of the related art, the temperature of the heater slowly increases and the overshoot does not occur. However, it takes longer for the temperature of the heater to reach the target temperature, e.g., 340° C., as compared with other control methods. 
     According to the temperature variation curve  670  of the heater according to the exemplary embodiment, a pre-heating speed may be faster than the PID method and at the same time, the overshoot that may occur when the electric power supplied to the heater is controlled by the fixed PWM control method does not occur. 
     Hereinafter, operations of the aerosol generator for controlling the temperature of the heater for each section according to the exemplary embodiment will be described in detail with reference to  FIGS. 5 and 6 . 
     The controller  110  controls the temperature of the heater  130  differently in a pre-heating temperature section and a temperature maintaining section. 
     The controller  110  controls the electric power supplied to the heater  130  by using the first method in the pre-heating temperature section. In detail, the controller  110  controls the electric power supplied to the heater  130  by the first method until the temperature of the heater reaches the upper limit of the pre-heating temperature section. 
     In some exemplary embodiments, the controller  110  may control the electric power supplied to the heater by the first method until the temperature of the heater reaches the upper limit from the lower limit of the pre-heating temperature section. According to an exemplary embodiment, a starting point where the controller  110  starts to control the heater by the first method is restricted to the lower limit of the pre-heating temperature section, and thus, the time when the controller  110  starts to control the electric power supplied to the heater by the first method becomes clear. The pre-heating temperature section is a temperature range including the lower limit and the upper limit, and referring to  FIG. 6 , the lower limit of the pre-heating temperature section may be 190° C. and the upper limit of the pre-heating temperature section may be 280° C. In some exemplary embodiments, the lower limit and the upper limit of the pre-heating temperature section may have other values than the above examples, e.g., 190° C. and 280° C. 
     Here, the first method may be a PWM control method with a fixed output. 
     In an exemplary embodiment, the controller  110  may check an output voltage range of the battery  120  and may heat the temperature to the upper limit of the pre-heating temperature section according to an upper limit of the output voltage range. Since the output voltage range of the battery  120  varies depending on malfunction or a charged amount, the controller  110  checks the output voltage range of the battery  120  and heats the heater as fast as possible according to the upper limit of the output voltage range, and thus faster pre-heating speed may be ensured as compared with the heater control method according to the related art. 
     On sensing that the temperature of the heater reaches the upper limit of the pre-heating temperature section, the controller  110  controls the electric power supplied to the heater by the second method until the temperature of the heater reaches the target temperature from the upper limit of the pre-heating temperature section. 
     Here, the target temperature is a temperature necessary for the heater in direct/indirect contact with the aerosol generating material to generate aerosol. The target temperature may be higher than the upper limit of the pre-heating temperature section. Referring to  FIG. 6 , the target temperature may be 340° C. The target temperature may be lower or higher than 340° C. 
     The second method is distinguished from the first method, and is a method of controlling the electric power supplied to the heater. For example, when the first method is the PWM control method, the second method may be the PID control method. The controller  110  may receive the temperature profile and the PID control instructions stored in the storage device  170 , and may execute the PID control so that the temperature of the heater, which has rapidly increased to the upper limit of the pre-heating temperature section, may reach the target temperature at a relatively slow speed. In detail, the controller  110  may appropriately adjust gains of a proportional term, an integral term, and a derivative term in order to increase the temperature of the heater to the target temperature without generating overshoot of the heater. 
     The storage device  170  stores various information for performing the PID control. The various information stored in the storage device  170  may include a logic or algorithm for calculating an appropriate gain when the heater reaches a certain temperature at a certain time, as well as exemplary values of the gains of the proportional term, the integral term, and the derivative term for performing the PID control. 
     The controller  110  may determine that the temperature of the heater reaches the upper limit of the pre-heating temperature section by using a temperature sensor or a timer. The controller  110  may determine that the temperature of the heater reaches the upper limit of the pre-heating temperature section by reading a value of a temperature sensor connected to the heater. 
     Also, the controller  110  measures the time taken to control the electric power supplied to the heater by the first method by using a timer built in or connected thereto through wires, and when the controller  110  senses the lapse of time that is predicted as the time when the temperature of the heater reaches the upper limit based on the measurement result, the controller  110  may change the method of controlling the electric power supplied to the heater from the first method to the second method. For example, when the first method is the fixed PWM control method and the heater is a resistor, a resistivity of which is well known, the controller  110  may calculate the temperature of the heater, which rises in proportion to an amount of power supplied to the heater. Thus, the controller  110  may calculate the time taken for the temperature of the heater to reach the upper limit of the pre-heating temperature section from a current temperature of the heater. 
     In an alternative exemplary embodiment, the controller  110  may control the electric power supplied to the heater by the second method until the temperature of the heater reaches the target temperature from the upper limit of the pre-heating temperature section, based on a ratio of the upper limit of the pre-heating temperature section with respect to the target temperature, which is set in advance. For example, when the ratio of the upper limit of the pre-heating temperature section with respect to the target temperature (hereinafter, referred to as “control reference ratio”) is 0.8 and the upper limit of the pre-heating temperature section is 240° C., the controller  110  may control the electric power supplied to the heater by the second method until the temperature of the heater becomes 300° C. from 240° C. Here, setting of the control reference ratio as 0.8 is an example according to the exemplary embodiment of the disclosure, and thus, the control reference ratio may vary according to the exemplary embodiment, and the upper limit of the pre-heating temperature section, e.g., 240° C., may also vary. For example, the control reference ratio may be a value in the range of 0.65 to 0.95. 
     
       
         
           
             
               
                 
                   
                     T 
                     2 
                   
                   = 
                   
                     
                       T 
                       3 
                     
                     - 
                     
                       a 
                       * 
                       
                         ( 
                         
                           
                             T 
                             3 
                           
                           10 
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                      
                     
                         
                     
                      
                     1 
                   
                   ] 
                 
               
             
           
         
       
     
     Equation 1 above is an example used when the controller  110  determines a time point for changing the controlling method from the first method to the second method. In Equation 1, T2 denotes a temperature of the heater when the controller  110  starts to control the electric power supplied to the heater by the second method, that is, the upper limit of the pre-heating temperature section. T3 denotes a target temperature of the heater, and “a” denotes a proportional coefficient within a range of 1.5 to 2.5. 
     In Equation 1, “a” varies according to a control signal transmission cycle of the controller  110  transmitting a power control signal to the heater. The value of “a” is experimentally determined and increases in proportion to the control signal transmission cycle. In addition, the variable “a” corresponding to each control signal transmission cycle stored in the form of a table and may be called by the controller  110  to be used to calculate T2. 
     Assuming that the controller  110  transmits the power control signal to the heater at an interval of 10 milliseconds (ms) and controls the electric power supplied to the heater by the fixed PWM control method for fast pre-heating speed of the heater, overshoot of about 10% with respect to the target temperature occurs experimentally. As an example, when the power control signal in the PWM control method is transmitted to a heater having a target temperature of 300° C. at an interval of 10 ms, an overshoot occurs and a maximum temperature of the overshoot is 330° C. Therefore, in order to prevent the overshoot of the heater, the controller  110  needs to change the power control method with respect to the heater before the heater reaches the target temperature. 
     For example, when the proportional coefficient “a” is determined to be 2 when the interval at which the controller  110  transmits the power control signal to the heater is 10 ms and the target temperature of the heater is 300° C., the controller  110  changes the power control method when the temperature of the heater reaches 240° C., according to Equation 1. The proportional coefficient “a” increases in proportion to the control signal transmission cycle. As such, the longer the control signal transmission cycle is, the lower the temperature of the heater is than 240° C. when the controller  110  changes the power control method from the first method to the second method is the time when the temperature of the heater is lower than 240° C. In another example, if the proportional constant is 2.5 and the control signal transmission cycle is 100 ms, the controller  110  may change the power control method of the heater from the first method to the second method at the temperature of 225° C. 
     As described above, according to the disclosure, the controller  110  controls the electric power supplied to the heater by the first method, changes the power control method to the second method when the temperature of the heater reaches the upper limit of the pre-heating temperature section, and then, performs the power control on the heater to the target temperature. Therefore, faster pre-heating speed than that of the related art may be ensured, and thus, a sufficient amount of aerosol may be rapidly provided to the user. Moreover, since the overshoot of the heater may be prevented, an unpleasant smoking experience of the user due to carbonization of a medium (aerosol generating material) may be prevented in advance. 
     In particular, since the power control method with respect to the heater is changed from the first method to the second method taking into account the transmission cycle of the power control signal transmitted from the controller  110  to the heater and the target temperature at the same time as expressed by Equation 1, the controller included in the aerosol generator according to the exemplary embodiments may exactly determine the time point for maximizing the benefits of the fast pre-heating speed and prevention of the overshoot. 
       FIG. 7  is a flowchart illustrating an example of a method of controlling electric power supplied to a heater according to an exemplary embodiment of the disclosure. 
     Since the method illustrated with reference to  FIG. 7  may be implemented by the aerosol generator  10  of  FIG. 5 , descriptions below will be provided with reference to  FIG. 5  and descriptions that are already given above with reference to  FIGS. 5 and 6  are omitted. 
     When the battery  120  starts to supply electric power to the heater  130 , the controller  110  regularly checks the temperature of the heater  130  (S 710 ). 
     The controller  110  determines whether the temperature of the heater  130  is lower than the lower limit of the pre-heating section (S 720 ), and when the temperature of the heater  130  is lower than the lower limit of the pre-heating section, the controller  110  starts to raise the temperature of the heater  130  by heating the heater  130  by the first method (S 730 ). 
     According to the exemplary embodiment, operations S 710  and S 720  may be omitted, and in this case, the controller  110  controls the electric power supplied to the heater  130  by the first method from the time when the heater  130  starts to be heated. 
     After operation S 730 , the controller  110  determines whether the current temperature of the heater  130  has reached the upper limit of the pre-heating section (S 740 ) When the current temperature of the heater  130  has reached the upper limit of the pre-heating section, the controller  110  changes the control method of the electric power supplied to the heater  130  from the first method to the second method and controls the heater  130  to be continuously heated (S 750 ). As described above, in operation S 750 , the first method may be the PWM control method with a fixed output and the second method may be the PID control method. 
     The controller  110  checks whether the current temperature of the heater  130  has reached the target temperature (S 760 ), and when the current temperature of the heater  130  has reached the target temperature, the controller  110  controls the temperature of the heater  130  to be maintained at the target temperature by the second method (S 770 ). 
       FIG. 8  is a flowchart illustrating an example of a method of controlling electric power supplied to a heater according to another exemplary embodiment of the disclosure. 
     Since the method illustrated with reference to  FIG. 8  may be implemented by the aerosol generator  10  of  FIG. 5 , descriptions below will be provided with reference to  FIG. 5  and descriptions that are already given above with reference to  FIGS. 5 and 6  are omitted.  FIG. 8  is a flowchart illustrating an alternative exemplary embodiment, in which the controller  110  determines the power control method of the heater based on a timer, not a temperature sensor. 
     When the battery  120  starts to supply electric power to the heater  130 , the controller  110  regularly checks the temperature of the heater  130  (S 810 ). 
     The controller  110  determines whether the temperature of the heater  130  is lower than the lower limit of the pre-heating section (S 820 ). When the temperature of the heater  130  is lower than the lower limit of the pre-heating section, the controller  110  starts to raise the temperature of the heater  130  by heating the heater  130  by the first method (S 830 ). 
     According to the exemplary embodiment, operations S 810  and S 820  may be omitted, and in this case, the controller  110  controls the electric power supplied to the heater  130  by the first method from the time when the heater  130  starts to be heated. 
     In addition, the controller  110  checks a difference between the current temperature and the upper limit of the pre-heating temperature section, and calculates the time taken to reach the upper limit of the pre-heating temperature section from the current temperature (hereinafter, referred to as the “upper limit reaching time”) (S 840 ). 
     The controller  110  checks whether the upper limit reaching time has passed (S 850 ), and when the upper limit reaching time has elapsed, the controller  110  changes the control method of the electric power supplied to the heater  130  from the first method to the second method and continuously heats the heater  130  to raise the temperature of the heater  130  to the target temperature (S 860 ). In operation S 860 , the controller  110  calculates the time taken for the temperature of the heater  130  at the upper limit of the pre-heating temperature section to reach the target temperature (hereinafter, referred to as the “target temperature reaching time”). 
     The controller  110  checks whether the target temperature reaching time has elapsed (S 870 ). When the target temperature reaching time has passed, the controller  110  maintains the temperature of the heater  130  at the target temperature by the second method (S 880 ). In operation S 880 , if the second method is the PID control method, the controller  110  may appropriately adjust the PID gains (proportional term, integral term, and derivative term) to be different before and after the temperature reaches the target temperature. 
       FIG. 9  is a flowchart illustrating an example of a method of controlling electric power supplied to a heater according to another exemplary embodiment of the disclosure. 
       FIG. 9  illustrates a process in which the controller  110  uses the target temperature and the proportional coefficient as in Equation 1 or uses a certain ratio when determining the upper limit of the pre-heating temperature section for changing the power control method into the second method in  FIG. 7 . 
     The controller  110  heats the heater  130  by the first method (S 730 ) and calculates a ratio between the current temperature and the target temperature of the heater  130  (S 910 ). 
     The controller  110  checks whether the ratio of the current temperature with respect to the target temperature of the heater  130  is equal to a preset value (S 920 ). When the ratio between the current temperature and the target temperature of the heater  130  is equal to the preset value, the controller  110  changes the control method of the electric power supplied to the heater from the first method to the second method and then controls the battery  120  to continuously heat the heater  130  to raise the temperature of the heater (S 750 ). The preset value may be 0.8 or a certain value determined according to Equation 1 in operation S 920 . 
     When the ratio between the current temperature and the target temperature of the heater  130  is not equal to the preset value, the controller  110  controls the heater  130  to be heated by the first method so as to sufficiently raise the temperature of the heater  130  (S 930 ). 
       FIG. 10  is a graph illustrating a method of controlling a temperature of a heater in an aerosol generator according to sections. 
     Referring to  FIG. 10 , the graph includes boundary lines  1010   a ,  1010   b , and  1010   c  for illustrating sections that are partitioned according to the temperature of the heater, a temperature variation curve  1030  of the heater according to the related art, and a temperature variation curve  1050  of the heater according to an exemplary embodiment of the present invention. In  FIG. 10 , the transverse axis denotes time in seconds and the longitudinal axis denotes Celsius temperature. 
     According to the related art, the controller tends to use the PID control in order to prevent the temperature of the heater from rising excessively during the pre-heating. When the controller controls the temperature of the heater in the PID control method, the temperature of the heater slowly rises through a feedback algorithm peculiar to the PID and the heater reaches the target temperature, e.g., 300° C., after passing through a pre-heating section a that is set from 0 to 20 sec. When the temperature of the heater reaches 300° C., the controller enters a maintaining section a for maintaining the temperature of the heater at 300 C. However, according to the related art, the power control method of the controller is not changed at a boundary between the pre-heating section a and the temperature maintaining section a, but the temperature of the heater is controlled by adjusting gains of the proportional term, the integral term, and the derivative term according to the characteristics of the PID control. 
     According to the temperature variation curve  1030  of the heater according to the related art, the temperature of the heater steadily increases in the pre-heating section a as described above, reaches the target temperature, that is, 300° C., at 20 sec., and enters the temperature maintaining section a. The time taken for the heater to reach the target temperature (20 sec.) may vary depending on a material of the heater, an output voltage of the battery, etc., and the target temperature (300° C.) of the heater may also vary depending on the aerosol generating material. 
     On the other hand, according to the temperature variation curve  1050  according to the disclosure, the temperature of the heater rapidly increases in a pre-heating section b and reaches the target temperature, e.g., 300° C., at 4 sec., and then enters a temperature decreasing section. According to the disclosure, the controller  110  may use the PWM control method having a fixed output level in the pre-heating section b, without using the PID control method. 
     Here, the temperature decreasing section is not shown in the temperature variation curve  1030  of the heater according to the related art. The temperature decreasing section refers to a time period in which controller  110  controls the electric power supplied to the heater in order to decrease the temperature of the heater to the target temperature when the overshoot occurs by the heater temperature reaching the target temperature rapidly and exceeding the target temperature. According to the related art, there is no temperature decreasing section because there is no overshoot occurring in the heater, but according to the exemplary embodiment, the power controlling process of the controller  110  for rapidly removing the overshoot of the heater is included. 
     Then, when the temperature of the heater returns to the target temperature after the temperature decreasing section, the controller  110  enters a temperature maintaining section b in order to maintain the temperature of the heater constant. As described above, according to the exemplary embodiment of the disclosure, the pre-heating time may be greatly reduced and a sufficient amount of aerosol provided to the user may be ensured at an early stage. 
     Hereinafter, processes of operating the aerosol generator which controls the temperature of the heater for each section according to the exemplary embodiment will be described in detail with reference to  FIGS. 5 and 10 . The pre-heating section, the temperature decreasing section, and the temperature maintaining section may be respectively referred to as a first stage, a second stage, and a third stage, or may be respectively referred to as a first section, a second section, and a third section, given that controlling methods or section characteristics of respective sections are different from one another. 
     The controller  110  controls the temperature of the heater  130  differently in the pre-heating section, the temperature decreasing section, and the temperature maintaining section. 
     Here, the pre-heating section denotes a time period in which the temperature of the heater is lower than the target temperature. The pre-heating section may be a section for re-heating the heater when the temperature of the heater is lower than the target temperature because the user maintains the aerosol generator  100  in turned-off status or the electric power is not supplied to the heater since a predetermined time has passed after the aerosol generator  100  is turned on by the user. 
     The controller  110  may allow the electric power to be rapidly supplied to the heater by using a maximum output according to a status of the battery in the pre-heating section. Here, the status of the battery may collectively refer to factors that directly affect the amount of electric power supplied by the battery to the heater, e.g., an output voltage level of the battery, a charged amount of the battery, etc. The controller  110  may control the temperature of the heater to be rapidly increased in the fixed PWM control method when controlling the electric power of the battery to be supplied to the heater in the pre-heating section. In addition, in  FIG. 6 , the pre-heating section b of the aerosol generator  100  according to the disclosure is 4 sec., but the pre-heating section b may be increased or reduced according to the elements included in the aerosol generator  100 . 
     In addition, when the temperature of the heater reaches the target temperature, the controller  110  may change the method of controlling the electric power supplied to the heater from the method corresponding to the pre-heating section to the method corresponding to the temperature decreasing section. Here, the method corresponding to the pre-heating section and the method corresponding to the temperature decreasing section may be stored in the storage device  170  in the form of a temperature profile of the heater, and then may be delivered to the controller  110  according to the call of the controller  110 . The temperature decreasing section denotes a time period in which the controller  110  controls the heater to decrease the temperature of the heater when the overshoot occurs by the temperature of the heater exceeding the target temperature. The temperature to which the temperature of the heater having the overshoot has to decrease becomes the target temperature, which is 300° C. in the example of  FIG. 10 . 
     In the above processes, the controller  110  performs the PID control for decreasing the temperature of the heater to the target temperature after receiving the temperature profile and the PID control instructions stored in the storage device  170 , and in particular, the controller  110  may adjust the gain of the derivative term appropriately in order to decrease the temperature of the heater which already has exceeded the target temperature. The gains of the proportional term, the integral term, and the derivative term stored in the storage device  170  may be obtained in advance through experiments. Also, a gain calculation module (not shown) for the PID control may be included in the storage device  170  for calculating an appropriate gain at a certain temperature of the heater at a certain time point. 
     The controller  110  may include a temperature sensor that regularly or irregularly measures the temperature of the heater in order to distinguish the pre-heating section from the temperature decreasing section. Also, the controller  110  may include a timer for measuring lengths of the pre-heating section and the temperature decreasing section. The temperature of the heater and the lengths of the pre-heating section and the temperature decreasing section collected by the controller  110  may be stored in the storage device  170 , read by the call of the controller  110 , and used to calculate a controlling parameter by the controller  110 . 
     Lastly, the controller  110  controls the temperature of the heater to be maintained at the target temperature when the temperature of the heater, in which the overshoot has occurred, is decreased to the target temperature during the temperature decreasing section. The time period in which the controller  110  maintains the temperature of the heater at the target temperature may be defined as the temperature maintaining section. The controller  110  controls the electric power supplied to the heater by using the PID control method while the temperature of the heater is maintained at the target temperature, and when a preset time has passed, the controller  110  recognizes that the temperature maintaining section is ended and controls the electric power to the heater to be blocked. 
     The controller  110  calculates the control reference ratio by using at least two of the lengths of the pre-heating section, the temperature decreasing section, and the temperature maintaining section, and may control the electric power supplied to the heater based on the control reference ratio. 
     
       
         
           
             
               
                 
                   
                     K 
                     1 
                   
                   = 
                   
                     
                       t 
                       1 
                     
                     
                       t 
                       2 
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                      
                     
                         
                     
                      
                     2 
                   
                   ] 
                 
               
             
           
         
       
     
     Equation 2 shows an example of the control reference ratio that may be calculated by the controller  110 . In Equation 2, k1 denotes the control reference ration, t1 denotes the length of the pre-heating section, and t2 denotes the length of the temperature decreasing section. The controller  110  may calculate the control reference ratio according to Equation 2, and may appropriately adjust the length of the temperature decreasing section based on the calculated control reference ratio. 
       K 1 &lt;C 1   [Equation 3]
 
     Equation 3 shows an example in which the controller  110  compares the control reference ratio with a preset comparison control value. In Equation 3, k1 denotes the control reference ratio calculated according to Equation 2, and C1 denotes a comparison control value set in advance to be compared with the control reference ratio. The comparison control value may be stored in the storage device  170  and may be delivered to the controller  110  according to a request from the controller  110 . The comparison control value may be updated if necessary. 
     As an example, the comparison control value may have a value of 2. In this case, the length of the temperature decreasing section has to be greater than half the length of the pre-heating section, considering Equation 2 and Equation 3. Once the length of the pre-heating section is determined via the timer and the temperature sensor, the controller  110  may calculate how long the temperature decreasing section has to be maintained based on the length of the pre-heating section which is a constant. In detail, the controller  110  may determine the gains of the proportional term, the integral term, and the derivative term for performing the PID control, taking into account how many seconds at least has to be maintained for the temperature decreasing section. 
     When the temperature of the heater enters the temperature maintaining section after the pre-heating section and the temperature decreasing section, the controller  110  re-calculates and updates the control reference ratio based on the determined lengths of the pre-heating section and the temperature decreasing section, and may maintain the temperature maintaining section according to the updated control reference ratio. 
     
       
         
           
             
               
                 
                   
                     K 
                     2 
                   
                   = 
                   
                     
                       t 
                       2 
                     
                     
                       t 
                       3 
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                      
                     
                         
                     
                      
                     4 
                   
                   ] 
                 
               
             
           
         
       
     
     Equation 4 shows another example of the control reference ratio that may be calculated by the controller  110 . In detail, in Equation 4, k2 denotes an updated control reference ratio (hereinafter, referred to as “updated control reference ratio”) that is updated from k1. Also, t2 denotes a length of the temperature decreasing section, and t3 denotes a length of the temperature maintaining section. The controller  110  may calculate the control reference ratio according to Equation 4, and may appropriately adjust the length of the temperature maintaining section based on the calculated control reference ratio. 
     
       
         
           
             
               
                 
                   
                     K 
                     2 
                   
                   = 
                   
                     
                       
                         t 
                         1 
                       
                       + 
                       
                         t 
                         2 
                       
                     
                     
                       t 
                       3 
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                      
                     
                         
                     
                      
                     5 
                   
                   ] 
                 
               
             
           
         
       
     
     Equation 5 above shows another example of the updated control reference ratio that may be calculated by the controller  110 . In Equation 5, k2 denotes the updated control reference ratio, and t1 to t3 respectively denote lengths of the pre-heating section, the temperature decreasing section, and the temperature maintaining section. The controller  110  may calculate and update the control reference ratio according to Equation 4 or 5, and may appropriately adjust the length of the temperature maintaining section based on the updated control reference ratio. 
       K 2 &lt;C 2   [Equation 6]
 
     Equation 6 above shows an example in which the controller  110  compares the updated control reference ratio with a preset comparison control value. In Equation 6, k2 denotes the updated control reference ratio calculated according to Equation 4 or 5 above, and C2 denotes a comparison control value set in advance for comparison with the updated control reference ratio. The comparison control value may be stored in the storage device  170  and may be delivered to the controller  110  according to a request from the controller  110 . Also, the comparison control value may be updated if necessary. 
     As an example, the comparison control value may have a value of 1. In this case, the length of the temperature maintaining section has to be greater than the length of the temperature decreasing section, considering Equation 4 and Equation 6. Also, when the updated control reference ratio is calculated according to Equation 4, the comparison control value of 1 requires that the length of the temperature maintaining section be greater than the sum of the lengths of the pre-heating section and the temperature decreasing section. The controller  110  may selectively calculate the updated control reference ratio according to Equation 4 or Equation 5 above, in order to appropriately adjust the gain of the PID. 
     As described above, the length of the temperature maintaining section is restricted according to the lengths of the pre-heating section and the temperature decreasing section, and thus, carbonizing of the medium, which occurs when the temperature of the heater is maintained at the high temperature, may be reduced. According to the exemplary embodiment, a sufficient amount of aerosol may be rapidly provided to the user with a short period of pre-heating time, and moreover, the carbonizing of the medium may be reduced. As a result, the user may have a satisfactory aerosol smoking experience. 
     In an exemplary embodiment, the controller may determine lengths of the temperature decreasing section and the temperature maintaining section according to Equation 2, Equation 3, Equation 4, and Equation 6, and may control the temperature of the heater for each section. In an alternative exemplary embodiment, the controller may determine lengths of the temperature decreasing section and the temperature maintaining section according to Equation 2, Equation 3, Equation 5, and Equation 6, and may control the temperature of the heater for each section. As described above, the lengths of the temperature decreasing section and the temperature maintaining section are dependent upon the length of the pre-heating section that may vary depending on the material of the heater and an initial temperature of the heater. 
       FIG. 11  is a flowchart illustrating an example of a method of controlling a temperature of a heater in an aerosol generator according to sections, according to an exemplary embodiment of the disclosure. 
     Since the method illustrated with reference to  FIG. 11  may be implemented by the aerosol generator  10  of  FIG. 5 , descriptions below will be provided with reference to  FIG. 5  and descriptions that are already given above with reference to  FIGS. 5 and 10  are omitted. 
     The controller senses the temperature of the heater (S 1110 ), and checks whether the sensed temperature of the heater is lower than a target temperature set in advance (S 1120 ). 
     When the temperature of the heater is lower than the target temperature, the controller enters the pre-heating section to control the heater to be heated (S 1130 ). 
     The controller checks whether an overshoot of the heater is sensed while regularly or irregularly monitoring rising of the temperature of the heater through the temperature sensor (S 1140 ), and when the overshoot is sensed, the controller calculates the control reference ratio by using the lengths of the pre-heating section and the temperature decreasing section (S 1150 ). 
     The controller determines the length of the temperature decreasing section based on the calculated control reference ratio, and controls the heater to decrease the temperature during the temperature decreasing section (S 1160 ). 
     In an alternative exemplary embodiment, the controller may control the electric power supplied to the heater based on a result of comparing the control reference ratio with the preset comparison control value as described above with reference to  FIG. 10 . 
     The controller checks whether the temperature decreasing section is terminated based on the temperature of the heater or the lapse of time (S 1170 ). When the temperature decreasing section is terminated, the controller calculates the control reference ratio based on at least two of the pre-heating section, the temperature decreasing section, and the temperature maintaining section (S 1180 ). In operation S 1180 , the controller may use at least one of the temperature sensor or the timer in order to check the termination of the temperature decreasing section. 
     The controller updates the control reference ratio calculated in operation S 1150  to the control reference ratio calculated in operation S 1180 , determines the length of the temperature maintaining section based on the updated control reference ratio, and then, controls the temperature of the heater to be maintained at the target temperature during the temperature maintaining section (S 1190 ). 
       FIG. 12  is a flowchart illustrating an example, in which a controller determines a period of a temperature reduction section. 
       FIG. 12  illustrates an alternative exemplary embodiment of operations S 1140  to S 1170  shown in  FIG. 11 , and hereinafter, descriptions will be provided with reference to  FIG. 11  for convenience of description. 
     When the controller senses the overshoot of the heater (S 1140 ), the controller calculates the control reference ratio by using the lengths of the pre-heating section and the temperature decreasing section (S 1150 ). 
     The controller compares the control reference ratio calculated in operation S 1150  with the comparison control value, e.g.,  2  (S 1210 ). 
     When the control reference ratio is equal to or greater than 2 in operation S 1210 , the controller changes the length of the temperature decreasing section by adjusting the gain of the PID control method (S 1220 ). The control reference ratio may be re-calculated through operation S 1150 , due to operation S 1220 . 
     When the control reference ratio is less than 2 in operation S 1210 , the controller controls the temperature of the heater to be decreased during the temperature decreasing section determined based on the calculated control reference ratio (S 1160 ). 
       FIG. 13  is a flowchart illustrating an example, in which a controller determines a period of a temperature maintaining section. 
       FIG. 13  illustrates an alternative exemplary embodiment of operations S 1170  to S 1190  shown in  FIG. 11 , and hereinafter, descriptions will be provided with reference to  FIG. 11  for convenience of description. 
     Once the controller senses that the temperature decreasing section is terminated (S 1170 ), the controller calculates the updated control reference ratio based on at least two of the lengths of the pre-heating section, the temperature decreasing section, and the temperature maintaining section (S 1180 ). 
     The controller determines whether the updated control reference ratio calculated in operation S 1180  is less than 1 (S 1310 ). 
     When the updated control reference ratio is equal to or less than 1, the controller changes the length of the temperature maintaining section by adjusting the gain of the PID control (S 1320 ). The updated control reference ratio may be re-calculated through operation S 1180 , due to operation S 1320 . 
     When the updated control reference ratio is less than 1, the controller controls the temperature of the heater to be maintained at the target temperature during the temperature maintaining section determined based on the updated control reference ratio calculated by the controller (S 1390 ). 
       FIG. 14  is a graph for describing differences between the method of controlling the temperature of the heater differently in the pre-heating section and the maintaining section and the method of controlling the temperature without dividing the sections according to the related art, and issues of the method of controlling the temperature for each section. 
     Referring to  FIG. 14 , the graph shows the variation in the temperature of the heater  130  according to the method of controlling the temperature of the heater  130  differently in the pre-heating section and the maintaining section, and the variation in the temperature of the heater  130  according to the method of controlling the temperature of the heater  130  for the entire section without distinction between the pre-heating section and the maintaining section. Also, when the temperature of the heater is controlled differently in the pre-heating section and the maintaining section, the target temperature of the heater  130  is set as a constant value. 
     The controller  110  may control the temperature of the heater  130  to be maintained at a reference temperature. The reference temperature may denote a temperature that is suitable for generating aerosol from the cigarette  200 . The reference temperature may set differently according to the kind of the cigarette  200 . For example, the reference temperature may be set between 240° C. and 360° C. 
     The controller  110  may set the target temperature and control the temperature of the heater  130  to reach the target temperature. The target temperature may be set to be the same as the reference temperature. However, one or more exemplary embodiments are not limited thereto, that is, the target temperature may be different from the reference temperature for appropriately controlling the temperature of the heater  130 . 
     In the case of the method of controlling the temperature of the heater  130  differently in the pre-heating section and the maintaining section, the controller  110  may control the electric power supplied to the heater  130  so that the temperature of the heater  130  is equal to or greater than the reference temperature in the pre-heating section. The pre-heating section may refer to a time period in which the heater  130  is heated to be equal to or greater than the reference temperature. Referring to the example shown in  FIG. 14 , the reference temperature is set to be 300° C. and the section before the temperature of the heater  130  is greater than the reference temperature corresponds to the pre-heating section. 
     In the pre-heating section, the controller  110  may control the electric power supplied to the heater  130  so that the temperature of the heater  130  is equal to or greater than the reference temperature within a short period of time. For example, the controller  110  may set a frequency and a duty cycle of a current pulse supplied from the battery  120  to the heater  130  through a pulse-width modulation to the maximum values. 
     In the case of the method of controlling the temperature of the heater  130  differently in the pre-heating section and the maintaining section, the controller  110  may set the target temperature of the heater  130  and control the electric power supplied to the heater  130  so that the temperature of the heater  130  is maintained at the reference temperature in the maintaining section. The maintaining section may denote a section after the pre-heating section is terminated when the temperature of the heater  130  is equal to or greater than the reference temperature. Referring to the example of  FIG. 14 , the section after the point when the temperature of the heater  130  is greater than the reference temperature, e.g., 300° C., may correspond to the maintaining section. 
     In the maintaining section, the controller  110  may set the target temperature. In particular, the controller  110  may set the target temperature at the point when the pre-heating section is terminated and the maintaining section starts. Referring to the example of  FIG. 14 , the target temperature is set at the point when the pre-heating section is terminated and the maintaining section starts, and is maintained constant thereafter. Also, the target temperature is set to be equal to the reference temperature, e.g., 300° C. 
     In the maintaining section, the controller  110  may control the electric power supplied to the heater  130  to decrease the temperature of the heater  130 , which has increased greater than the reference temperature within a short period of time, to the reference temperature of the heater  130 . In particular, coefficients of the PID control method may be set by the controller  110  such that the temperature of the heater  130  may be reduced to and maintained at the reference temperature. Referring to the example of  FIG. 14 , the temperature of the heater  130  which has increased to higher than the reference temperature through the pre-heating section is reduced in the maintaining section. 
     In the maintaining section, by the PID coefficients set to reduce the temperature of the heater  130 , the temperature of the heater  130  may decrease to be equal to or lower than the reference temperature. Since the heater  130  is heated to be equal to or higher than the reference temperature within the short period of time in the pre-heating section, the time for the temperature of the heater  130  to reach the reference temperature or higher may be reduced. However, it may be difficult to maintain the temperature of the heater  130  at the reference temperature in the maintaining section. 
     Referring to the example of  FIG. 14 , as the smoking is executed, the temperature of the heater  130  is gradually decreased below the reference temperature. Since the cigarette  200  may sufficiently generate the aerosol at the reference temperature, the temperature of the heater  130  decreasing below the reference temperature may cause degradation of smoking quality. 
     The controller  110  may adjust the target temperature in order to compensate for the temperature of the heater  130 , which is decreased below the reference temperature. The compensation of the temperature of the heater  130  may be performed in the manner that the temperature of the heater  130  is increased by the extent that the temperature of the heater  130  decreases below the reference temperature. 
     In order to address the issue that the temperature of the heater  130  is decreased below the reference temperature, which occurs when the target temperature is maintained constant without being adjusted, the controller  110  may adjust the target temperature in various manners. Accordingly, the controller  110  may compensate for the temperature of the heater  130 , which decreases below the reference temperature, so as to maintain the temperature of the heater  130  close to the reference temperature. 
     The controller  110  may adjust the target temperature in the temperature decreasing section, in which the temperature of the heater  130  decreases below the reference temperature. The controller  110  may adjust the target temperature at the time point when the temperature of the heater  130  decreases below the reference temperature and the temperature decreasing section starts. Alternatively, the controller  110  may adjust the target temperature before or after the temperature decreasing section starts. 
     The controller  110  may adjust the target temperature in real-time. The controller  110  may determine the target temperature in real-time based on the temperature variation of the heater  130 , etc. However, one or more exemplary embodiments are not limited thereto, that is, the controller  110  may change the target temperature to another value only once. 
     Since the controller  110  compensates for the temperature of the heater  130  by adjusting the target temperature, the temperature of the heater  130  may be maintained around the reference temperature, and accordingly, degradation in the smoking quality due to the decrease in the temperature may be prevented. Therefore, since the pre-heating section and the maintaining section are divided, the time taken to prepare the aerosol generator  10  for providing the user with the aerosol may be reduced, and at the same time, since the heater  130  is heated within a short period of time in the pre-heating section, the reduction in the temperature of the heater  130  in the maintaining section may be prevented. 
     Referring to  FIG. 14 , the method of controlling the temperature of the heater  130  throughout the entire section without dividing the pre-heating section and the maintaining section is shown. When the pre-heating section and the maintaining section are not divided, the temperature dropping as the smoking proceeds may not occur, but the time taken for the temperature of the heater  130  to reach the reference temperature increases longer than that in a case in which the pre-heating section and the maintaining section are divided, and accordingly, the time for preparing the aerosol generator  10  may increase. Referring to the example of  FIG. 14 , when the pre-heating section and the maintaining section are not divided, it takes more time for the temperature of the heater  130  to reach the reference temperature than the case in which the pre-heating section and the maintaining section are divided. 
       FIG. 15  is a graph illustrating an example of adjusting a target temperature according to one or more exemplary embodiments of the disclosure. 
     The controller  110  may adjust the target temperature by changing the target temperature once. Referring to the example of  FIG. 15 , the target temperature is changed to a greater constant value when the temperature decreasing section starts, and the temperature of the heater  130  is controlled accordingly. 
     When the target temperature is adjusted by changing the target temperature once, the temperature of the heater  130  may be maintained closer to the reference temperature as compared with a case in which the target temperature is not adjusted. Also, due to a simple process of adjusting the target temperature, power consumption may be reduced and a circuit structure of the controller  110  may be simplified. 
       FIG. 16  is a graph illustrating another example of adjusting a target temperature according to one or more exemplary embodiments of the disclosure. 
     The controller  110  may adjust the target temperature by changing the target temperature linearly. Referring to the example of  FIG. 16 , the target temperature is increased linearly from the time point when the temperature decreasing section starts, and the temperature of the heater  130  is controlled accordingly. 
     When the target temperature is adjusted by changing the target temperature linearly, the temperature of the heater  130  may be maintained closer to the reference temperature as compared with a case in which the target temperature is not adjusted. Also, since it is not complicated for the controller  110  to adjust the target temperature in this way, the power consumption may be reduced and circuit design may be easy. 
     The target temperature may be simply adjusted in the method illustrated in FIGS.  15  and  16  to compensate for the temperature of the heater  130 , but when the smoking is performed for a long time period, there may be a difference between the temperature of the heater  130  and the reference temperature. Thus, a method of more precisely adjusting the target temperature may be suggested. In the process of designing the control method and the aerosol generator  10  according to the disclosure, values shown as examples in  FIG. 17  may be utilized to adjust the target temperature. 
       FIG. 17  is a graph illustrating an accumulated value obtained by accumulating a difference value between a temperature of a heater and a target temperature with the lapse of time, according to one or more exemplary embodiments of the disclosure. 
     Referring to  FIG. 17 , an accumulated value obtained by accumulating differences between the temperature of the heater  130  and the target temperature with the lapse of time is shown. In a section in which the temperature of the heater  130  is greater than the target temperature, the difference value has a positive value and the accumulated value may increase. In a section in which the temperature of the heater  130  is lower than the target temperature, the difference value has a negative value and the accumulated value may decrease. Therefore, the accumulated value of  FIG. 17  may be the maximum at the point when the temperature of the heater  130  decreases below the target temperature. 
     The controller  110  may adjust the target temperature based on the accumulated value that is obtained by accumulating the difference value between the temperature of the heater  130  and the target temperature with the lapse of time. The controller  110  may calculate the difference value between the temperature of the heater  130 , which is measured in real-time, and the target temperature. Also, the controller  110  may calculate the accumulated value by accumulating the difference value, and adjust the target temperature based on the accumulated value. Therefore, the difference value, the accumulated value, and the target temperature affect one another, and may be calculated and changed in real-time by the controller  110 . 
     For example, the controller  110  may calculate a reduction degree of the accumulated value from the maximum value of the accumulated value, and may adjust the target temperature by adding the decreased value that is obtained by multiplying the reduction degree by a constant to the initial value. The initial value may be the same as the target temperature set by the controller  110  in the maintaining section. The target temperature may be adjusted so that the section in which the accumulated value decreases in  FIG. 17  may increase in an inverted form. The detailed method of adjusting the target temperature and the temperature of the heater  130 , which is compensated for according to the adjusting of the target temperature, are shown in  FIG. 6 . 
       FIG. 18  is a graph illustrating an example of adjusting a target temperature based on a variation in an accumulated value, according to one or more exemplary embodiments of the disclosure. 
     The controller  110  may continuously adjust the target temperature based on the variation in the accumulated value.  FIG. 18  shows the variation in the temperature of the heater  130  when the target temperature is adjusted based on the variation in the accumulated value and the variation in the temperature of the heater  130  when the target temperature is not changed but maintained constant. 
     As the controller  110  adjusts the target temperature based on the variation in the accumulated value, the temperature of the heater  130  may be maintained close to the reference temperature even when the user smokes the aerosol. Therefore, the aerosol generator  10  may generate the aerosol evenly from the cigarette  200  without degradation in the smoking quality even when the time passes. 
       FIG. 19  is a graph illustrating another example of adjusting a target temperature based on a variation in an accumulated value, according to one or more exemplary embodiments of the disclosure. 
     Referring to  FIG. 19 , another example of adjusting the target temperature based on the variation in the accumulated value is shown. As in the example of  FIG. 18 , the controller  110  may calculate the accumulated value by accumulating the difference value between the temperature of the heater  130  and the target temperature according to the time lapse, and as shown in  FIG. 19 , the controller  110  may adjust the target temperature based on the variation in the accumulated value. 
     However, unlike the example of  FIG. 18 , in which the controller  110  adjusts the target temperature based on the variation in the accumulated value, the controller  110  may discontinuously adjust the target temperature based on the variation in the accumulated value. Even when the target temperature is discontinuously adjusted, the temperature of the heater  130  may be maintained close to the reference temperature. 
     The method in which the controller  110  continuously adjusts the target temperature based on the variation in the accumulated value may provide more precise compensation for the temperature of the heater  130 , as compared with the method in which the target temperature is discontinuously adjusted. However, when the controller  110  discontinuously adjusts the target temperature based on the variation in the accumulated value, the temperature of the heater  130  may be appropriately compensated for while reducing the calculation amount of the controller  110 . 
       FIG. 20  is a flowchart illustrating a method of controlling a temperature of a heater for heating a cigarette accommodated in the aerosol generator according to one or more exemplary embodiments of the disclosure. 
     Referring to  FIG. 20 , the method of controlling the temperature of the heater for heating the cigarette accommodated in the aerosol generator  10  may include processes that are sequentially processed in the aerosol generator  10  of  FIG. 1 . Therefore, it will be understood that the descriptions given above with respect to the aerosol generator  10  shown in  FIG. 1  also apply to the method of controlling the temperature of the heater for heating the cigarette of  FIG. 8 , although the descriptions are omitted below. 
     In operation  52010 , the aerosol generator  10  may control the electric power supplied to the heater, so that the temperature of the heater may be equal to or greater than the reference temperature that is suitable for generation of aerosol from the cigarette. 
     In operation  52020 , the aerosol generator  10  may set the target temperature of the heater and control the electric power supplied to the heater so that the temperature of the heater is maintained at the reference temperature. In operation  52020 , the aerosol generator  10  may adjust the target temperature in order to compensate for the temperature of the heater when the temperature of the heater decreases below the reference temperature. 
     One or more of the above exemplary embodiments may be embodied in the form of a computer program that may be run in and/or executed by a computer through various elements, and the computer program may be recorded on a non-transitory computer-readable recording medium. Examples of the non-transitory computer-readable recording medium include magnetic media (e.g., hard disks, floppy disks, and magnetic tapes), optical media (e.g., CD-ROMs and DVDs), magneto-optical media (e.g., floptical disks), and hardware devices specifically configured to store and execute program commands (e.g., ROMs, RAMs, and flash memories). 
     Meanwhile, the computer programs may be specially designed or well known to one of ordinary skill in the computer software field. Examples of the computer programs may include not only machine language code but also high-level language code which is executable by various computing means by using an interpreter. 
     The particular implementations shown and described herein are illustrative examples of the disclosure and are not intended to otherwise limit the scope of the disclosure in any way. For the sake of brevity, electronics, control systems, software, and other functional aspects of the systems according to the related art may not be described in detail. Furthermore, the connecting lines or connectors shown in the drawings are intended to represent example functional relationships and/or physical or logical couplings between the various elements. It should be noted that many alternative or additional functional relationships, physical connections, or logical connections may be present in a practical device. Moreover, no item or component is essential to the practice of the present disclosure unless the element is specifically described as “essential” or “critical”. 
     The singular forms “a,” “an” and “the” in the specification of the exemplary embodiments, in particular, claims, may be intended to include the plural forms as well. Unless otherwise defined, the ranges defined herein is intended to include values within the range as individually applied and may be considered to be the same as individual values constituting the range in the detailed description. Finally, operations constituting methods may be performed in appropriate order unless explicitly described in terms of order or described to the contrary. The present disclosure is not limited to the described order of the steps. The use of any and all examples, or example language (e.g., “such as”) provided herein, is intended merely to better illuminate the present disclosure and does not pose a limitation on the scope of the present disclosure unless otherwise claimed. Also, those of ordinary skill in the art will readily appreciate that many alternations, combinations and modifications, may be made according to design conditions and factors within the scope of the appended claims and their equivalents. 
     INDUSTRIAL APPLICABILITY 
     One or more exemplary embodiments of the disclosure may be used to manufacture and implement electronic tobacco devices providing a user with feeling of smoking.