RU2787539C2 - Method for control of heating in aerosol generating system - Google Patents

Abstract

FIELD: tobacco industry.

SUBSTANCE: method for control of heating in aerosol generating system (100) containing heater (119) includes: the first control stage, at which set power is supplied to heater (119), and resistance of heater (119) is determined, wherein certain resistance indicates a heater temperature; a set condition is tracked, and, when the set condition is detected, resistance of heater (119) is registered; target resistance (R_T) is determined, corresponding to a target temperature of heater (119), based on registered resistance; and the second control stage, at which power supplied to heater (119) is adapted in a controllable way to bring resistance of heater (119) to target resistance (R_T), and, thus, heater (119) is brought to the target temperature corresponding to target resistance (R_T).

EFFECT: obtainment of an aerosol generating system with controllable heating.

20 cl, 9 dwg

Description

The present invention relates to a method for controlling heating in an aerosol generating system comprising a heater, as well as such an aerosol generating system. In particular, the invention relates to hand held electrical aerosol generating systems that vaporize an aerosol generating substrate by heating to generate an aerosol.

Aerosol generating electrical systems are known. Such systems typically consist of a device part having a battery and control electronics, an aerosol generating substrate, an electrical heater containing at least one resistive heating element configured to heat the aerosol generating substrate, and a mouthpiece. In some systems, the aerosol-forming substrate contains a liquid and an elongated wick is used to transport the liquid aerosol-forming substrate to the heater. The heater typically comprises a coil of resistive heating wire wound around an elongated wick. The heater, wick, and aerosol-forming liquid substrate are often contained in a cartridge that may be attached to or housed in the device part. When the user activates the device, an electrical current passes through the heater, causing resistive heating, which causes the liquid in the wick to evaporate. By inhaling or puffing through the mouthpiece, air is drawn through the system and captures vapor, which is then cooled to form an aerosol. Air containing the aerosol leaves the system through the mouthpiece and enters the user's mouth.

In the context of this document, the term "aerosol generating substrate" means a substrate capable of releasing volatile compounds that can form an aerosol. Such volatile compounds may be released by heating the aerosol-forming substrate. The aerosol generating substrate may conveniently be part of the aerosol generating article or system.

In general, it is desirable that aerosol generating systems be able to produce an aerosol that remains uniform for some time. This is especially important if the aerosol is intended for human consumption, as variations in the aerosol can impair the user's experience, and large variations can be potentially harmful. It is also generally desirable that aerosol generating systems produce the aerosol as efficiently as possible within the amount of energy required to generate the aerosol. However, this is difficult to achieve due to variations in the manufacturing process of the systems, variations in the properties of the aerosol forming substrates used in such systems, and the different operating conditions in which the systems are used.

In aerosol generating systems using an aerosol-forming liquid substrate, it is also desirable to be able to detect and avoid a "dry heat" situation, i.e., a situation in which the heater is heated in the presence of an insufficient amount of aerosol-forming liquid substrate. This situation is also known as "dry puff" and can lead to overheating and potentially thermal degradation of the aerosol-forming liquid substrate, whereby undesirable by-products such as formaldehyde can be formed.

To produce a uniform aerosol, it may be necessary to control or regulate the temperature of the heater used to heat the aerosol-forming substrate.

The purpose of the present invention is to provide an aerosol generating system by which an aerosol with more uniform properties is generated during heating of the aerosol generating substrate. A further object of the present invention is to provide an aerosol generating system that heats the aerosol generating substrate more efficiently and reduces the chance of dry puffing.

According to a first aspect of the present invention, there is provided a method for controlling heating in an aerosol generating system comprising a heater, the method comprising: a first control step of applying a predetermined power to the heater and determining a resistance of the heater, the determined resistance being indicative of the temperature of the heater; tracking a given condition and, when a given condition is detected, registering the resistance of the heater; determining a target resistance corresponding to a target heater temperature based on the detected resistance; and a second control step in which the power supplied to the heater is controlled in a controlled manner to bring the resistance of the heater to the target resistance, so that the heater is driven to the target temperature corresponding to the target resistance.

One possibility of controlling or controlling the temperature of the heater is power control. In a power controlled system, a predetermined or constant power is applied to the heater and the resistances of the heater are monitored. Since the relationship between the electrical resistance of the heater and the temperature of the heater is generally known or can be determined, the resistance of the heater may provide an indication of the temperature of the heater. For example, the electrical resistance of a heater may be known to be proportional to the temperature of the heater, in which case there will be a substantially linear relationship between resistance and temperature.

When a given or constant power is applied, the temperature of the heater will first increase rapidly, for example within about 0.3 seconds, towards the target temperature. Typically, the power is chosen such that the temperature of the heater begins to stabilize around the target temperature. However, at lower power, it is usually necessary to maintain the temperature of the heater at the target temperature, rather than at the level needed to heat it up. Therefore, if constant power is continued to be supplied to the heater, the temperature of the heater will continue to rise for some time above the target temperature, but at a slower rate. By monitoring the resistance, it is possible to reduce or stop power to the heater if the resistance becomes too high, i.e. if the temperature of the heater rises above the target temperature. However, in power controlled systems, the heater temperature tends to exceed the target temperature. This may be undesirable as it may result in increased aerosol generation and therefore variability in aerosol delivery as the user inhales. In addition, exceeding the target temperature means energy consumption, which negatively affects the efficiency of the device.

Another possibility to control or regulate the temperature of the heater is resistance control. In resistance controlled systems, a target resistance is set indicative of the target temperature and the power supplied to the heater is adjusted so that the heater resistance moves towards or stays within the target resistance region. However, temperature control through the use of resistance control can be problematic because there are difficulties in calculating the target resistance due to various factors that negatively affect heater resistance, such as manufacturing variations, contact resistance variability, varying properties of the aerosol generating substrate, different ambient temperatures, and different geometries, materials and resistance values of various heaters.

The method according to the first aspect of the present invention uses two control steps to control heating in an aerosol generating system: a first control step that is based on power control and a second control step that is based on resistance control. As a result, a hybrid control method is obtained, which means that the advantages of both types of control can be used, and at the same time, a number of disadvantages of each type can be reduced. Such a hybrid method provides a number of beneficial effects, such as the following.

At the first stage of control, based only on power regulation, it is necessary to supply constant power to the heater and determine the resistance of the heater. There is no need to adjust the power during this control step and therefore it is relatively easier to control and use fewer control resources compared to resistance control. This is advantageous during the initial stages of the heating cycle, i.e. while the heater is merely warming up, as there is less need for temperature control during this time.

When a predetermined condition is detected, the resistance is recorded, and the registered resistance can be used to determine a target resistance based on the registered resistance. Because the target resistance is based simply on the heater resistance recorded at the time the setpoint was detected, the target resistance can be determined regardless of various factors that might otherwise negatively impact heater resistance, such as manufacturing variations, contact resistance variability, varying properties. aerosol generating substrate, different ambient temperatures and different geometries, materials and resistance values of different heaters.

Once the target resistance is determined, a second step of control based on resistance control may be performed in which the power supplied to the heater is controlled in a controlled manner to bring the heater resistance to the target resistance so that the heater is driven to the target temperature corresponding to the target resistance. This reduces the likelihood of the heater temperature exceeding the target temperature. Therefore, the stability or uniformity of the properties of the generated aerosol is improved both during one breath and during subsequent breaths. For example, it is possible to stabilize the volume of the delivered aerosol as well as the constituents contained in the aerosol. This provides an overall improved user experience. In addition, by reducing the number of temperature rises, less energy is consumed and system efficiency is improved.

In the context of this document, the term "target resistance" refers to the electrical resistance of the heater, which is determined based on the resistance of the heater, registered when a given condition is detected. As discussed above, since the relationship between the electrical resistance of the heater and the temperature of the heater is generally known or can be determined, the resistance of the heater may provide an indication of the temperature of the heater. Therefore, the target resistance has a corresponding target temperature, and vice versa.

In the context of this document, the term "target temperature" refers to the temperature or temperature range corresponding to the target resistance. The target temperature is sufficient to generate an aerosol from the aerosol-forming substrate, but is below the temperature at which thermal decomposition of the aerosol-forming substrate occurs or unwanted by-products are formed.

The method may move from the first control stage to the second control stage when a predetermined condition is detected. This provides a fast response to a given condition.

As used herein, the term "preset condition" refers to a condition or criterion that indicates that the heater resistance is at or near the target resistance. The condition may be known or determined before the method is executed. As described above, when power is applied to the heater, the temperature, and hence the resistance of the heater, initially increases rapidly before stabilizing at approximately the target temperature. The point at which the resistance begins to stabilize can be monitored, and various points within the stabilization are set as a predetermined condition.

The predetermined condition may be selected from one or more different conditions, such as the following.

As one example, the predetermined condition may be the elapsed time from the start of the user's inhalation. The time taken for the resistance to stabilize at or near the target temperature value may be known or determined, and this time may be used as a predetermined condition.

As another example, the predetermined condition may be a derivative of a resistance that is less than a predetermined threshold. In the context of the present invention, the term "resistance derivative" refers to a measurement of sensitivity to a change in resistance relative to a change in another variable. For example, the derivative may represent the rate of change of resistance over time, such as a resistance gradient vs. time curve, or the derivative may represent the absolute change in resistance over sampling time. As the resistance begins to stabilize around the target temperature, the rate of change of resistance begins to decrease over time. The predetermined condition may be a specific value for the rate of change of resistance, and the method can monitor when the rate of change of resistance falls below this value.

In yet another example, the predetermined condition may be a zero derivative of the resistance. When the heater temperature has reached the highest temperature, it will reach the set power, the temperature change rate and thus the resistance change rate will become zero. This zero rate of change of resistance can be used as a given condition.

In addition, the predetermined condition may be any suitable criterion based on resistance and/or time.

The first control step and the second control step may be performed during the user's inhalation, and optionally during each user's inhalation or puff. This ensures that the target resistance is set and efficient optimization is performed for each breath. This is particularly useful if the target resistance tends to change between puffs, for example if the aerosol generating substrate is used up or the operating environment changes rapidly.

In the context of this document, the terms "inhale" and "puff" are used interchangeably and are intended to refer to the act of the user puffing through the end of the system to draw aerosol out of the system.

The first control step and the second control step may be performed during the first breath of the user, and only the second control step may be performed during the second and subsequent breaths of the user. This ensures that the target resistance is set on the user's first breath and used for all subsequent breaths, thus obtaining a uniform aerosol on all subsequent breaths in a particular user session. If necessary, the temperature of the heater can be increased to the target temperature faster than the first control stage, which is based on power regulation, since the second control stage is not limited to the need to supply constant power. In other words, the power can be increased beyond the constant power according to the first control step, if the system so requires, to more quickly bring the temperature of the heater to the target temperature.

The target resistance may be determined after a few initial breaths by the user. Optionally, during the initial few breaths of the user, only the first control step and the step of monitoring and detecting a predetermined condition and registering resistance can be performed. To do this, switching to the second control mode will occur between breaths, and not during inspiration.

The target resistance may be determined based on the average of the recorded resistances from the user's initial few breaths. The target resistance, based on the average of the recorded resistances from several initial breaths of the user, may provide a match or correction for variation in the initially recorded resistances, for example, upon initial activation of the aerosol generating system, before the system thermally stabilizes, or if operating environmental conditions change abruptly when activated, such as when the user moves from outdoors to indoors.

With user breaths after several initial user breaths, only the second stage of control may be performed and the target resistance may be based on an average of the recorded resistances from several initial user breaths. This can provide a uniform aerosol for subsequent breaths in a particular user session. If necessary, the temperature of the heater can be increased to the target temperature faster than the first control stage, which is based on power regulation, since the second control stage is not limited to the need to supply constant power.

According to a second aspect of the present invention, an aerosol generating system is provided, comprising: a heater; power unit; and controller; moreover, the controller is configured to: supply a given power to the heater and determine the resistance of the heater in the first control mode, while the determined resistance indicates the temperature of the heater; monitoring the predetermined condition and, upon detecting the predetermined condition, registering the resistance of the heater; determining a target resistance corresponding to a target heater temperature based on the detected resistance; and in a controlled manner adjusting the power supplied to the heater to bring the resistance of the heater to the target resistance in the second control mode, thereby bringing the heater to the target temperature corresponding to the target resistance.

In the system according to the second aspect of the present invention, two control modes are used to control heating in the aerosol generating system: a first control mode based on power control and a second control mode based on resistance control. The first and second control modes correspond to the first and second steps of the method according to the first aspect of the present invention. Therefore, the system is capable of hybrid temperature control, which means that the advantages of both types of control can be used, and at the same time, a number of disadvantages of each type can be reduced. Such hybrid regulation provides a number of beneficial effects, which are described above in the first aspect of the present invention and, for brevity, are not repeated here.

The controller may be configured to switch from the first control mode to the second control mode upon detecting a predetermined condition. This provides a fast response to a given condition.

The predetermined condition may be selected from one or more of the following: i) time elapsed from the start of the user's inspiration; ii) the derivative of the resistance is less than a given threshold value; and iii) the derivative of the resistance is zero. Each of the predetermined conditions is the same as the predetermined conditions for the first aspect of the present invention and are described above. For brevity, this description is not repeated here. In addition, the predetermined condition may be any suitable criterion based on resistance and/or time.

The first control mode and the second control mode may be used during the user's inhalation, and optionally during each user's inhalation. This ensures that the target resistance is set and efficient optimization is performed for each breath. This is particularly useful if the target resistance tends to change between puffs, for example if the aerosol generating substrate is used up or the operating environment changes rapidly.

The first control mode and the second control mode may be used during the first breath of the user, and during the second and subsequent breaths of the user, only the second control mode may be used. This ensures that the target resistance is set on the user's first breath and used for all subsequent breaths, thus obtaining a uniform aerosol on all subsequent breaths in a particular user session. If necessary, the temperature of the heater can be increased to the target temperature faster than in the first control mode, which is based on power regulation, because the second control mode is not limited to the need to supply constant power. In other words, the power can be increased beyond the constant power according to the first control mode, if the system so requires, to more quickly bring the temperature of the heater to the target temperature.

The target resistance may be determined after a few initial breaths by the user. Optionally, during the implementation of several initial breaths of the user, only the first mode can be used, as well as monitoring and detecting a given condition and registering resistance. To do this, switching to the second control mode will occur between breaths, and not during inspiration.

The target resistance may be determined based on the average of the recorded resistances from the user's initial few breaths. The target resistance, based on the average of the recorded resistances from the user's initial few breaths, may provide for matching or correcting for variation in the determined target resistance, for example, upon initial activation of the aerosol generating system before the system thermally stabilizes, or if operating environmental conditions change abruptly when activated, such as when the user moves from outdoors to indoors.

For user breaths after several initial user breaths, only the second control mode may be used, and the target resistance may be based on an average of the recorded resistances from several initial user breaths. This can provide a uniform aerosol for subsequent breaths in a particular user session. If necessary, the temperature of the heater can be increased to the target temperature faster than in the first control mode, which is based on power regulation, because the second control mode is not limited to the need to supply constant power.

In both the first and second aspects of the present invention, the heater may comprise an electrically resistive heating element. The heater may comprise an electrically resistive material. Suitable electrically resistive materials include, but are not limited to: semiconductors such as doped ceramics, electrically "conductive" ceramics (such as, for example, molybdenum disilicide), carbon, graphite, metals, metal alloys, and composite materials made from a ceramic material and a metal material. Such composite materials may contain alloyed or unalloyed ceramics. Examples of suitable doped ceramics include doped silicon carbides. Examples of suitable metals include titanium, zirconium, tantalum, platinum, gold and silver. Examples of suitable metal alloys include stainless steel, nickel, cobalt, chromium, aluminum, titanium, zirconium, hafnium, niobium, molybdenum, tantalum, tungsten, tin, gallium, manganese, gold and iron alloys as well as nickel, iron, cobalt, stainless steel, Timetal® and iron-manganese-aluminum superalloys. In composite materials, the electrically resistive material may optionally be embedded in, encapsulated in, or coated with the insulating material, or vice versa, depending on the energy transfer kinetics and the desired external physicochemical properties.

In both the first and second aspects of the present invention, the heater may comprise an internal heating element or an external heating element, or both internal and external heating elements, where the terms "internal" and "external" refer to a position relative to the aerosol generating substrate. The inner heating element may be of any suitable shape. For example, the inner heating element may be in the form of a heating plate. Alternatively, the internal heater may be in the form of a jacket or substrate having various electrically conductive portions, or in the form of an electrically resistive metal tube. Alternatively, the internal heating element may be one or more heating needles or rods that extend through the center of the aerosol generating substrate. Other alternatives include heating wire or filament such as Ni-Cr (chromium nickel), platinum, tungsten or alloy wire or heating plate. Optionally, the internal heating element may be applied internally or externally to the rigid carrier material. In one such embodiment, the electrically resistive heating element may be made using a metal having a particular relationship between temperature and resistivity. In such an exemplary device, the metal may be formed into a track on a suitable insulating material, such as ceramic material, and then sandwiched between two layers of another insulating material, such as glass. The heaters thus formed can be used both for heating and for monitoring the temperature of the heating elements during operation.

The heater may include a fluid-permeable heating element. The fluid-permeable heating element may be substantially flat and may comprise electrically conductive filaments. Electrically conductive threads may be in the same plane. In other embodiments, the substantially flat heating element may be curved along one or more dimensions, such as forming a domed shape or a bridge shape.

The electrically conductive filaments may form spaces between the filaments, and the voids may have a width of 10 µm to 100 µm. The filaments can create a capillary effect in the voids so that, in use, the aerosol forming liquid substrate is drawn into the voids, increasing the area of contact between the heating element and the liquid.

The electrically conductive filaments can form a grid of 160 to 600 US mesh (+/- 10%) (i.e., 160 to 600 threads per inch (+/- 10%)). The width of the gaps is preferably between 75 µm and 25 µm. The percentage of open area of the mesh, which is the ratio of the area of the gaps to the total area of the mesh, is preferably 25 to 56%. The mesh can be formed using different types of wicker or lattice structures. Alternatively, the electrically conductive filaments consist of an array of filaments arranged parallel to each other.

The electrically conductive filaments may have a diameter of 10 µm to 100 µm, preferably 8 µm to 50 µm, and more preferably 8 µm to 39 µm. The filaments may have a circular cross section or may have a flattened cross section. The heater filaments may be formed by etching a sheet material such as foil. If the heater assembly comprises a mesh or woven web of filaments, the filaments may be obtained individually and knitted together.

The area of the fluid-permeable heating element may be, for example, less than or equal to 50 square millimeters, preferably less than or equal to 25 square millimeters, more preferably about 15 square millimeters.

The electrical resistance of the grid, matrix or woven fabric of electrically conductive filaments of the heating element can be from 0.3 ohms to 4 ohms. Preferably, the electrical resistance is equal to or greater than 0.5 ohm. More preferably, the electrical resistance of the grid, matrix or woven web of electrically conductive filaments is between 0.6 and 0.8 ohms.

The aerosol-forming substrate may be an aerosol-forming liquid substrate. If an aerosol generating liquid substrate is provided, the aerosol generating system preferably includes liquid retention means. For example, an aerosol-forming liquid substrate may be held in a liquid storage portion or container. Alternatively or additionally, the aerosol-forming liquid substrate may be absorbed into the porous carrier material. The porous carrier material may be made from any suitable absorbent plug or piece, such as foamed metal or plastic material, polypropylene, terylene, nylon fibers, or ceramic.

If an aerosol-forming liquid substrate is provided, both the first and second aspects of the present invention can be configured to detect a dry puff, for example, by detecting when the detected resistance increases above a threshold value, or by detecting when the power required to maintain the target resistance heater drops below the threshold.

The aerosol-forming substrate may be a solid aerosol-forming substrate. Alternatively, the aerosol-forming substrate may contain both solid and liquid components. The aerosol-forming substrate may comprise a tobacco-containing material containing volatile tobacco flavor compounds that are released from the substrate upon heating. Alternatively, the aerosol forming substrate may comprise a non-tobacco material. The aerosol generating substrate may further comprise an aerosol generating agent. Examples of suitable aerosol forming agents are glycerin and propylene glycol.

The aerosol generating system may include a housing having a mouthpiece and a main body. The main body may include an electrical power supply, such as a rechargeable lithium ion battery, a control circuit having a controller, such as a microcontroller, and a user interface for actuating the heater, such as a puff detection device or a push button. The mouthpiece may include a liquid storage portion, such as a cartridge containing a liquid substrate that generates an aerosol. The cartridge may include capillary material for transferring the aerosol-forming liquid substrate to the heater. The cartridge may also contain a heater.

The control circuit may be designed to supply power to the heating element in the form of a series of electrical voltage pulses. The power supplied to the heating element can then be controlled by adjusting the duty cycle of the voltage pulses. The duty cycle can be adjusted by changing the pulse width or the pulse frequency, or both. Alternatively, the control circuit may be designed to supply power to the heating element in the form of a continuous DC signal. A proportional-integral-derivative (PID) control loop can be used to drive the heater resistance to the target resistance.

According to a third aspect of the present invention, there is provided a controller for an aerosol generating system, the controller being capable of performing any of the methods described above.

According to a fourth aspect of the present invention, there is provided a computer program that, when executed on a programmable controller for an aerosol generating system, causes the programmable controller to perform any of the methods described above.

The features described in relation to one aspect can be equally applied to other aspects of the present invention.

Embodiments of the present invention will now be described solely as examples with reference to the accompanying drawings, in which:

in fig. 1 is a schematic representation of an aerosol generating system according to an embodiment of the present invention;

in fig. 2 is a schematic representation of a temperature profile of a heater of an aerosol generating system obtained by a method according to an embodiment of the present invention;

in fig. 3 is a schematic representation of a temperature profile of a heater of an aerosol generating system obtained by a method according to another embodiment of the present invention;

in fig. 4 is a schematic representation of a temperature profile of a heater of an aerosol generating system obtained by a method according to another embodiment of the present invention;

in fig. 5 is a schematic representation of a temperature profile of a heater of an aerosol generating system obtained by a method according to another embodiment of the present invention;

in fig. 6 is a schematic representation of a temperature profile of a heater of an aerosol generating system obtained by a method according to another embodiment of the present invention;

in fig. 7 is a schematic representation of a heater temperature profile of an aerosol generating system illustrating a dry puff scenario;

in fig. 8 is a schematic representation of the heater temperature profile of an aerosol generating system showing another dry puff scenario;

in fig. 9 is a schematic diagram of a temperature control circuit for an aerosol generating system of the type shown in FIG. 1.

In FIG. 1 shows a schematic representation of an aerosol generating system. The system 100 includes a body 101 having a mouthpiece 103 and a main body 105. In the main body 105, an electric power supply 107 such as a rechargeable lithium ion battery, a control circuit 109 having a controller 110 such as a microcontroller, and a puff detection device 111 are provided. In the mouthpiece 103, a liquid storage portion 113 is provided, such as a cartridge containing an aerosol generating liquid substrate 115, a wick 117 made of a capillary material, and a heater 119 containing at least one heating element. One end of the wick 117 extends into the cartridge 113 and the other end of the wick 117 is surrounded by a heater 119. The heater 119 is connected to the puff detecting device 111 via connectors 121, which in turn are connected to the control circuit 109 via additional connectors (not shown). ). The housing 101 also includes an air inlet 123 in the region of the puff detecting device 111, an air outlet 125 which is located at the outlet of the mouthpiece 103, and an aerosol chamber 127 surrounding the heater 119.

The aerosol-forming liquid substrate 115 is conveyed or carried by the wick 117 via capillary action from the cartridge 113 to the end of the wick which is surrounded by the heater 119. In use, the user inhales or puffs through the mouthpiece 103, ambient air is drawn in through the air inlet 123 . The inhalation or puff is detected or sensed by the puff detecting device 111 which activates the heater 119. The battery 107 supplies power to the heater 119 to heat the end of the wick 117 surrounded by the heater. The liquid at this end of the wick 117 is vaporized by the heater 119 to create supersaturated vapor. At the same time, the evaporated liquid is replaced by another liquid moving along the wick 117 by capillary action. The generated supersaturated vapor mixes with and is carried in the air flow from the air inlet 123 and condenses in the aerosol generating chamber 127 to form an inhalable aerosol which is carried to the outlet 125 and into the user's mouth.

The controller 110 is programmable and has embedded software or firmware to control the power supplied to the heater 119 to control its temperature. This in turn affects the temperature profile of the heater, which will affect the amount of aerosol produced. The controller 110 supplies power to the heater 119 through pulse width modulation (PWM), which uses a series of electrical voltage pulses to transmit power. The power supplied to the heater can be varied by varying the duty cycle of the pulses at a constant frequency. The duty cycle is the ratio of the time period in which power is supplied to the time period in which power is not supplied. In other words, it is the ratio of the voltage pulse width to the time between voltage pulses. For example, a low duty cycle of 5% will provide significantly less power than a duty cycle of 95%.

In FIG. 2 shows a plot of resistance R versus time t and a temperature profile of a heater of an aerosol generating system that is heated by a method according to an embodiment of the present invention. In particular, in FIG. 2 shows data for the first three breaths or puffs in a user session in which all three breaths are controlled by hybrid control, ie a combination of power control and resistance control.

The system starts at time t₀, for example, when the user turns on the system. The user starts the first breath or puff at time t₁which activates the heater. The heater is initially controlled by a first step or control mode based on power control (indicated in the figures PR) in which the heater is supplied with a constant setpoint power corresponding to a given duty cycle. The set power can be relatively high, such as 80% to 95% duty cycle, to rapidly increase the temperature of the heater. Applying a given power causes the heater temperature to rise and the heater resistance to be detected at regular intervals to provide an indication of the heater temperature. The specified power is supplied to the heater until the specified condition is detected at time t_L1, in which the resistance is fixed or recorded, and the target resistance R_T1 determined based on the recorded resistance. In general, the target resistance will be the same as the registered resistance, although it is also possible that the target resistance will differ from the registered resistance, for example by a function of the registered resistance, or include a known adjustment for deviations depending on the requirements of the system. Using this method, the target resistance is determined independently of any variations in heater resistance or system characteristics. The target resistance corresponds to the target temperature to which the heater should be heated.

In the example of FIG. 2, the predetermined condition is the point at which the rate of change of resistance falls below a particular threshold, ie, the point at which the temperature profile gradient decreases to the predetermined value. In particular, in FIG. 2, the predetermined condition is the point at which the temperature profile gradient approaches zero.

At time t _L1 , the heater control enters a second stage or resistance-based control mode (denoted as RR in the figures) in which the power supplied to the heater is controlled in a controlled manner to bring the heater resistance to the target resistance R _T1 , thus the heater is driven to the target temperature corresponding to the target resistance R _T1 . The second stage or control mode uses PID control to control the resistance. PID control is embedded in the software programmed into the controller. For resistance control, the heater resistance is determined and the deviation between the determined resistance and the target resistance R _T1 is calculated. The power duty cycle is then corrected using PID control to correct the deviation and bring the heater to the target resistance. The resistance is determined at a frequency selected to match the frequency at which the duty cycle is controlled, and may be determined once every 100 ms or more frequently as needed.

After entering the second stage or control mode based on the resistance control at time t _L1 , the resistance is kept substantially constant at the target resistance value R _T1 until the user stops their first breath or puff at time t ₂ .

In the example of FIG. 2 for each subsequent breath or puff use a similar hybrid control as described above. The user takes the second and third breaths at times t ₃ and t ₅ , respectively, and the respective target resistances R _T2 and R _T3 are determined at times t _L2 and t _L3 , respectively. In FIG. 2 each of the three breaths has its own target resistance, i.e. R _T1 , R _T2 and R _T3 respectively. The target resistances are essentially similar, but slightly different to account for slightly different conditions for each breath, so the target resistances R _T1 , R _T2 and R _T3 are optimized for each breath.

In FIG. 3 shows a plot of resistance R versus time t and a temperature profile of a heater of an aerosol generating system that is heated by a method according to another embodiment of the present invention. In particular, in FIG. 3 shows data for the first three breaths or puffs in a user session in which only the first breath is controlled by hybrid control and the second and subsequent breaths are controlled using resistance control alone.

In FIG. 3 shows that the system is started at time t ₀ and the user begins to take the first breath or puff at time t ₁ which activates the heater. The first breath, as shown in Fig. 3 are adjusted in the same way as the breaths shown in FIG. 2. During the first breath, the heater is initially controlled by the first step or control mode based on the power control. When a predetermined condition is detected at time t _L1 , the resistance is recorded and the target resistance R _T is determined based on the detected resistance. At this point, the heater control enters the second stage or resistance-based control mode, which is used for the remaining breaths until the breath stops at time t ₂ .

As shown in FIG. 3, the second and third breaths start at times t ₃ and t ₅ respectively, at which times the heater is again activated but controlled by a second control step based on resistance control only, until the breaths stop at times t ₄ and t ₆ respectively. Therefore, the second and third breaths are adjusted based on the target resistance R _T for the first breath. This ensures that a uniform aerosol is generated for all breaths. In addition, the heater can be more quickly brought to the target temperature corresponding to the target resistance R _T if necessary, because the second stage or control mode is not limited to supplying a constant set power, but can supply power with a duty cycle of up to 100%, if necessary, to bring the temperature of the heater to the target temperature as soon as possible. As can be seen in FIG. 3, the temperature profiles of the second and third breaths have steeper gradients compared to the first breath, indicating a faster rate of temperature change. In the second stage or control mode used to control the second and third breaths, a PID control is used to control the resistance, which is embedded in the software programmed in the controller.

In FIG. 4 shows a plot of resistance R versus time t and a temperature profile of a heater of an aerosol generating system that is heated by a method according to another embodiment of the present invention. In particular, in FIG. 4 shows data for the first five breaths or puffs in a user session in which the first three breaths are controlled by hybrid control and the fourth and subsequent breaths are controlled using resistance control alone.

In FIG. 4 shows that the system is started at time t ₀ and the user begins to take the first breath or puff at time t ₁ at which the heater is activated. The first breath, as shown in Fig. 4 are adjusted in the same way as the breaths shown in FIG. 2. During the first breath, the heater is initially controlled by a first stage or control mode based on power regulation, in which the heater is supplied with a constant set power corresponding to a given duty cycle. The predetermined power is supplied to the heater until the predetermined condition is detected at the time t _L1 at which the resistance R ₁ is fixed or recorded. The predetermined condition in the example of FIG. 4, again, represents the point at which the temperature profile gradient approaches zero. The target resistance at this point is not determined. Instead, the method first monitors one or more additional breaths or puffs before determining the target resistance.

As shown in FIG. 4, at time t _L1 , the control of the heater enters the second stage or control mode based on resistance control, in which the power supplied to the heater is controlled in a controlled manner to bring the resistance of the heater to the detected resistance R ₁ , thus the heater is brought to a temperature corresponding to the registered resistance R ₁ . The second stage or control mode uses PID control, which is embedded in the software programmed in the controller, to control the resistance.

After entering the second stage or control mode based on the resistance control at time t _L1 as shown in FIG. 4, the resistance is kept substantially constant at the value of the registered resistance R ₁ until the user stops their first breath or puff at time t ₂ .

The second and third breaths, as shown in Fig. 4, adjust in the same way as the first breath. The second and third breaths start at times t ₃ and t ₅ respectively, at which the heater is again activated. The heater is first controlled by the first step or control mode based on power control, and when a predetermined condition is detected at times t _L2 and t _L3 , the resistances R ₂ and R ₃ are respectively recorded. The heater control then proceeds to a second stage or resistance control based control mode which is used for the remaining breaths until the second and third breaths are terminated at times t ₄ and t ₆ respectively.

The three separate recorded resistances R ₁ , R ₂ and R _{3 of} the first three breaths are used to determine the target resistance R _T , which is based on the average of the three recorded resistances R ₁ , R ₂ and R ₃ . The fourth and fifth breaths are adjusted in the same manner as the second and third breaths, which are shown in FIG. 3. As shown in FIG. 4, the fourth and fifth breaths start at times t ₇ and t ₉ respectively, at which times the heater is again activated but controlled by a second control step based only on resistance control until the breaths stop at times t ₈ and t ₁₀ respectively. The fourth and subsequent breaths are adjusted using the target resistance R _T , which is based on the average of the recorded resistances R ₁ , R ₂ and R ₃ . This ensures that a homogeneous aerosol is generated for the fourth and subsequent breaths.

In FIG. 5 shows a plot of resistance R versus time t and a temperature profile of a heater of an aerosol generating system that is heated by a method according to another embodiment of the present invention. In particular, in FIG. 5 shows data for the first seven breaths or puffs in a user session in which the first five breaths are controlled by hybrid control and the sixth and subsequent breaths are controlled by resistance control only. This method can be used if the recorded resistance for the first few puffs varies significantly, i.e., the resistance variation is outside the specified or acceptable range, which can occur, for example, during the initial activation of the aerosol generating system, before thermal stabilization of the system.

In FIG. 5 shows that the system is started at time t ₀ and the user begins to take the first three breaths or puffs at times t ₁ , t ₃ and t ₅ , respectively, at which the heater is activated. The first three breaths, as shown in Fig. 5 are adjusted in the same way as the first three breaths shown in FIG. 4. During the first three breaths, the heater is initially controlled by the first step or control mode based on the power control. For each breath, a separate resistance is recorded, i.e. R ₁ , R ₂ and R ₃ respectively, upon detection of a predetermined condition for each breath at times t _L1 , t _L2 and t _L3 respectively. At these points, heater control shifts to a second step or control mode using resistance control based on the three respective recorded resistances R ₁ , R ₂ and R ₃ , the step or mode being used for the remaining of each of the breaths until the breath stops at times t ₂ , t ₄ and t ₆ respectively.

The condition for determining the target resistance may be that the recorded resistance for the nth number of last breaths or puffs falls within the maximum predetermined range ΔRmax. If so, then the target resistance can be based either on the last recorded resistance or on the average of the nth number of last breaths.

As shown in FIG. 5, n is set to 3 and the resistance values R ₁ , R ₂ and R ₃ are outside the maximum predetermined range ΔR _max . In other words, the maximum value of R ₁ , R ₂ and R ₃ minus the minimum value of R ₁ , R ₂ and R ₃ is greater than the maximum specified range ΔR _max i.e. Max {R ₁ , R ₂ and R ₃ } - Min {R ₁ , R ₂ and R ₃ } > ΔR _max . Accordingly, the method does not determine the target resistance, but monitors the further breath taken by the user.

The fourth breath is taken at time t ₇ and adjusted in the same way as the first three breaths, ie using hybrid control. The fourth resistance R ₄ is detected upon detection of the predetermined condition at time t _L4 and the fourth breath is stopped at time t ₈ . The method then checks the recorded resistances for the last three breaths, ie R ₂ , R ₃ and R ₄ . However, as shown in FIG. 5, these three resistances are also outside the maximum predetermined range ΔR _max . Therefore, the method does not determine the target resistance, but monitors the next breath taken by the user.

The fifth breath is taken at time t ₉ and adjusted in the same way as the first four breaths, ie using hybrid control. The fifth resistance R ₅ is detected upon detection of the predetermined condition at time t _L5 and the fourth breath is stopped at time t ₁₀ . The method then checks the recorded resistances for the last three breaths, ie R ₃ , R ₄ and R ₅ . As shown in FIG. 5, these three resistance values fall within the maximum predetermined range ΔR _max and hence the target resistance R _T can be determined. The target resistance R _T may either be based on the last recorded resistance, ie R ₅ , or may be based on the average of the recorded resistances of the last three breaths, ie R ₃ , R ₄ and R ₅ . In FIG. 5 shows that the target resistance R _T is based on the average of the recorded resistances of the last three breaths, ie R ₃ , R ₄ and R ₅ .

The sixth and seventh breaths are adjusted in the same manner as the second and third breaths, which are shown in FIG. 3. As shown in FIG. 5, the sixth and seventh breaths start at times t ₁₁ and t ₁₃ respectively, at which times the heater is again activated but controlled by a second control step based on resistance control only, until the breaths stop at times t ₁₂ and t ₁₄ respectively. The sixth and subsequent breaths are adjusted using the target resistance R _T , which is based on the average of the recorded resistances R ₃ , R ₄ and R ₅ . This ensures that a homogeneous aerosol is generated for the sixth and subsequent breaths.

In FIG. 6 shows a plot of resistance R versus time t and a temperature profile of a heater of an aerosol generating system that is heated by a method according to another embodiment of the present invention. In particular, in FIG. 6 shows data for the first five breaths or puffs in a user session in which the first three breaths are controlled by power control only and the sixth and subsequent breaths are controlled by resistance control alone.

The first three breaths, as shown in Fig. 6 differ from the initial breaths of the other examples shown in the figures in that they are controlled by power control alone. In FIG. 6 shows that the system is started at time t ₀ and the user begins to take the first breath or puff at time t ₁ at which the heater is activated. During inhalation, the heater is initially controlled by a first stage or power control based control mode in which the heater is supplied with a constant predetermined power corresponding to a predetermined duty cycle until inhalation is stopped at time t ₂ . When a predetermined condition is detected at time t _L1 , resistance R ₁ is recorded. The predetermined condition in the example of FIG. 6 represents the point at which the temperature profile gradient approaches zero.

As mentioned above, a power controlled system typically uses a relatively high set power, such as 80% to 95% duty cycle, to raise the heater temperature to the target temperature as quickly as possible. Once the target temperature is reached, the power may be gradually reduced because the heater typically requires less power to maintain the target temperature than it does to heat it up. However, since the first breath during its execution does not switch to the second stage or control mode, i.e. upon detection of a given condition, the resistance is not adjusted to the level of the registered resistance and, therefore, the temperature of the heater continues to rise above the registered resistance, although with less speed.

The target resistance, based on the registered resistance R ₁ , may be determined upon detection of a predetermined condition, i.e., at time t _L1 . For example, the target temperature may be determined if R ₁ is within a predetermined range. However, in the method shown in FIG. 6 take an alternative approach and first monitor two additional breaths or puffs using power control alone before determining a target resistance to account for resistance variation over the first few breaths.

The second and third breaths, as shown in Fig. 6, adjust in the same way as the first breath. The second and third breaths start at times t ₃ and t ₅ respectively, at which the heater is again activated. The heater is controlled through the first step only or control mode based on power control only, until inhalation stops at times t ₄ and t ₆ , respectively. When a predetermined condition is detected at times t _L2 and t _L3 , the resistances R ₂ and R ₃ are recorded accordingly.

The three recorded resistances R ₁ , R ₂ and R _{3 of} the first three breaths are used to determine the target resistance R _T , which is based on the average of the three recorded resistances R ₁ , R ₂ and R ₃ . The fourth and fifth breaths are adjusted in the same manner as the second and third breaths, which are shown in FIG. 3, i.e. using resistance control only. As shown in FIG. 6, the fourth and fifth breaths start at times t ₇ and t ₉ respectively, at which times the heater is again activated but controlled by a second control step based only on resistance control until the breaths stop at times t ₈ and t ₁₀ respectively. The fourth and subsequent breaths are adjusted using the target resistance R _T , which is based on the average of the recorded resistances R ₁ , R ₂ and R ₃ . This ensures that a homogeneous aerosol is generated for the fourth and subsequent breaths.

Alternatively, if the three recorded resistances R ₁ , R ₂ and R ₃ are not within the maximum predetermined range, the system may wait for the resistance to stabilize and fall within the predetermined range before calculating the target resistance based on the average of the recorded resistances in a manner similar to the method described in connection with FIG. five.

In FIG. 7 shows a plot of resistance R versus time t and a temperature profile of an aerosol generating system heater according to an embodiment of the present invention, in which the heater exhibits a dry puff scenario. In particular, in FIG. 7 shows data for the first three breaths or puffs in a user session in which all breaths are controlled by hybrid control, ie a combination of power control and resistance control. As described above, a "dry puff" or "dry heat" situation occurs when the heater is heated in the presence of an insufficient amount of aerosol-forming liquid substrate. This can lead to overheating and potentially thermal decomposition of the aerosol-forming liquid substrate, resulting in the formation of undesirable by-products such as formaldehyde.

In FIG. 7 shows that the system is started at time t ₀ and the user begins to take the first breath or puff at time t ₁ which activates the heater. During the first breath, liquid is present in the heater, which is initially controlled by the first step or power control based control mode. When the predetermined condition is detected at time t _L1 , the resistance R ₁ is detected and the target resistance can be determined based on the detected resistance R ₁ . At this point, the heater control enters the second stage or resistance-based control mode, which is used for the remaining breaths until the breath stops at time t ₂ .

The second and third breaths, as shown in Fig. 7 is adjusted in the same manner as the first breath and starts at times t ₃ and t ₅ respectively. However, insufficient aerosol-generating liquid substrate is available for the second and third breaths and dry puff occurs. When the predetermined condition is detected, resistance R ₂ is recorded at time t _L2 during the second breath and resistance R ₃ is recorded at time t _L3 during the third breath. The resistances R ₂ and R ₃ are noticeably higher than the resistance R ₁ due to dry puffs. This is due to the fact that in a power controlled system the heater is supplied with a constant setpoint power, and if there is not enough aerosol-forming liquid substrate present in the heater, for example, if the cartridge in which the aerosol-forming liquid substrate is stored is empty, there will be a marked increase in the reached limit temperature and hence in the registered resistance, since less or no power is expended to evaporate the liquids. In addition, the temperature will rise at a higher rate than when fluid is present, as evident from the sharply increased rate of temperature rise for the second and third breaths.

The system is configured to detect this marked increase in registered resistance due to the presence of insufficient liquid. In particular, the system is configured to detect when the registered resistance rises above a threshold value. When detected, the system is able to isolate the heater to prevent further dry puffs, thereby reducing the likelihood of the user being exposed to unwanted by-products. Dry puff detection and heater isolation commands can be implemented by software programmed into the controller.

In FIG. 8 shows a plot of resistance R versus time t and a temperature profile of an aerosol generating system heater according to an embodiment of the present invention in which the heater exhibits another dry puff scenario. In particular, in FIG. 8 shows data for the first three breaths or puffs in a user session in which the first breath is controlled by hybrid control and subsequent breaths are controlled by resistance control.

In FIG. 8 shows that the system is started at time t ₀ and the user begins to take the first breath or puff at time t ₁ which activates the heater. The first breath, as shown in Fig. 8 is adjusted in the same way as the first breath, which is shown in FIG. 7. During the first breath, liquid is present in the heater, which is initially controlled by the first stage or control mode based on power control. When a predetermined condition is detected at time t _L1 , the resistance is recorded and the target resistance R _T is determined based on the detected resistance. At this point, the heater control enters the second stage or resistance-based control mode, which is used for the remaining breaths until the breath stops at time t ₂ .

For the second and third breaths, not enough aerosol-generating liquid substrate is available in the heater, and therefore a dry puff occurs. As shown in FIG. 8, the second and third breaths start at times t ₃ and t ₅ , respectively, at which times the heater is again activated but controlled by a second resistance-based control stage in which the resistance is adjusted to the target resistance R _T the first breath until the breaths stop at times t ₄ and t ₆ respectively. Because the system adjusts the power for the second and third breaths to keep the resistance constant, it is not possible to use the change in resistance to detect a dry puff scenario as it is kept constant. Instead, it is necessary to monitor the power level required to maintain the target resistance and therefore maintain the target temperature. When an insufficient amount of liquid aerosol generating substrate is present in the heater, the amount of power required to maintain a constant temperature will be markedly less than when liquid is present, since no power is expended to vaporize the liquid.

The system is configured to detect a noticeable reduction in power required to maintain the target heater resistance. In particular, the system is configured to detect when the power required to maintain the target heater resistance drops below a threshold value. When detected, the system is able to isolate the heater to prevent further dry puffs, thereby reducing the likelihood of the user being exposed to unwanted by-products. Dry puff detection and heater isolation commands can be implemented by software programmed into the controller.

In FIG. 9 shows a control circuit 200 used to provide the described temperature control, according to one embodiment of the invention.

The control circuit 200 includes a heater 214 comprising a resistive heating element connected to an electrical power supply via a connector 222. The electrical power supply provides voltage V2 . A series resistor 224 with known resistance r is placed in series with heater 214. In the circuit, V1 is present at the point between heater 214 and series resistor 224, i.e., on the ground side of heater 214. Voltage V1 is an intermediate value between ground and voltage V2 . Temperature control software is embedded in software programmed into microcontroller 218 that can deliver a PWM voltage signal through output 230 of microcontroller 218 to transistor 226 that functions as a conventional switch to actuate heater 214 in response to the signal. voltage with pulse-width modulation.

The temperature reading of the heater 214 (in this example, the electrical resistance of the heater 214) is determined by measuring the electrical resistance of the heater 214. The temperature reading is used to adjust the duty cycle of the PWM voltage applied to the heater 214 to keep the heater resistance near the target resistance. The temperature index is determined at a frequency selected to match the time required for the control process, and may be determined once every 100 ms or more often, depending on the need.

Analog input 221 on the microcontroller 218 is used to monitor the voltage V2 on the power supply side of the heater 214. Analog input 223 on the microcontroller is used to monitor the voltage V1 on the ground side of the heater 214.

The heater resistance to be measured at a certain temperature is R _heater . In order for microprocessor 218 to measure the resistance R _heater of heater 214, both the current through heater 214 and the voltage across heater 214 can be determined. Ohm's law can then be used to determine the resistance:

(1)

In FIG. 9, the voltage across the heater is V2-V1 and the current through the heater is I. In this way:

(2)

An additional resistor 224, whose resistance r is known, is used to determine the current I, again using Equation (1) above. The current through resistor 224 is also I, and the voltage across resistor 224 is V1. In this way:

(3)

So, combining (2) and (3) gives:

(four)

Thus, the microprocessor 218 can measure V2 and V1 as the aerosol generating system is used, and knowing the value of r can determine the heater resistance R _heater at a particular temperature.

The heater resistance R _heater is adjusted to the temperature. A linear approximation can be used to determine the temperature T corresponding to the measured resistance R of the _heater according to the following formula:

(five)

where A is the coefficient of thermal resistance of the heater material, and R ₀ is the resistance of the heater at ambient temperature T ₀ .

The advantage of the control circuit 200 is that there is no need for a temperature sensor. Such sensors can be bulky and expensive. Also, instead of temperature, the microcontroller can directly use the resistance value. If the resistance R _heater of the heater is kept within the required range, so will the temperature of the heater 214. Accordingly, the actual temperature of the heater 214 does not need to be calculated during the control process, which increases the efficiency of the calculations. However, a separate temperature sensor can be used and attached to the microcontroller to provide the necessary temperature information if required.

The software programmed into the microcontroller 218 is configured to monitor the predetermined condition and, upon detecting the predetermined condition, record the resistance of the heater. The set condition and resistance may be stored in a memory of microcontroller 218. Software programmed in microcontroller 218 is configured to determine a target resistance based on the registered resistance.

The microcontroller 218 is also configured to adjust the duty cycle of the PWM voltage signal to control the power supplied to the heater to bring the heater resistance to the target resistance so that the heater is driven to the target temperature corresponding to the target resistance. To adjust the resistance, the resistance R _heater of the heater is determined and the deviation between the determined resistance R _heater of the heater and the target resistance is calculated. The power duty cycle is then corrected using proportional-integral-derivative (PID) control to correct the deviation and bring the heater to the target resistance. PID control is embedded in the software programmed into the controller 218.

The power P provided to the heater 214 can be determined using the following formula:

P=VI (6)

where V is the voltage across the heater i.e. V2-V1 and I is the current through the heater which can be determined using equation (3) above. The determined power can be used, for example, to detect the dry puff scenario shown in FIG. 8.

Claims (37)

1. A method for controlling heat in an aerosol generating system comprising a heater, the method comprising a first control step in which a predetermined power is supplied to the heater and a resistance of the heater is determined, the determined resistance being indicative of the temperature of the heater; tracking a given condition and, when a given condition is detected, registering the resistance of the heater; determining a target resistance corresponding to a target heater temperature based on the detected resistance; and a second control step in which the power supplied to the heater is controlled in a controlled manner to bring the resistance of the heater to the target resistance, and thus the heater is brought to the target temperature corresponding to the target resistance. 2. The method according to claim 1, characterized in that the method moves from the first control stage to the second control stage when a predetermined condition is detected. 3. The method according to claim 1 or 2, characterized in that the given condition is selected from one or more of the following the time elapsed from the start of the user's inhalation; the derivative of the resistance is less than the specified threshold value; and the derivative of the resistance is zero. 4. The method according to any one of paragraphs. 1-3, characterized in that the first control step and the second control step are performed during the user's inhalation and optionally during each user's inhalation. 5. The method according to any one of paragraphs. 1-3, characterized in that the first control stage and the second control stage are performed during the first breath of the user, and at the same time, only the second control stage is used during the second and subsequent breaths of the user. 6. The method according to any one of paragraphs. 1-3, characterized in that the target resistance is determined after a few initial breaths of the user. 7. The method according to any one of paragraphs. 1-3, characterized in that during the implementation of several initial breaths of the user, only the first control stage and the stage of tracking and detecting a given condition and registering resistance are performed. 8. The method according to claim 6 or 7, characterized in that the target resistance is determined based on the average value of the registered resistances from several initial breaths of the user. 9. The method of claim 8, wherein for user breaths after several initial user breaths, only the second stage of control is used and the target resistance is based on the average of the recorded resistances from several initial user breaths. 10. An aerosol generating system comprising heater; power unit; and controller; wherein the controller is configured to supplying a predetermined power to the heater and determining the resistance of the heater in the first control mode, the determined resistance being indicative of the temperature of the heater; monitoring the predetermined condition and, upon detecting the predetermined condition, registering the resistance of the heater; determining a target resistance corresponding to a target heater temperature based on the detected resistance; and adjusting in a controlled manner the power supplied to the heater to bring the resistance of the heater to the target resistance in the second control mode, and thereby bring the heater to the target temperature corresponding to the target resistance. 11. An aerosol generating system according to claim 10, characterized in that the controller is configured to switch from the first control mode to the second control mode when a predetermined condition is detected. 12. An aerosol generating system according to claim 10 or 11, characterized in that the predetermined condition is selected from one or more of the following the time elapsed from the start of the user's inhalation; the derivative of the resistance is less than the specified threshold value; and the derivative of the resistance is zero. 13. An aerosol generating system according to any one of paragraphs. 10-12, characterized in that the first control mode and the second control mode are used during inhalation of the user and optionally during each inhalation of the user. 14. An aerosol generating system according to any one of paragraphs. 10-12, characterized in that the first control mode and the second control mode are used during the first breath of the user, and at the same time only the second control mode is used during the second and subsequent breaths of the user. 15. An aerosol generating system according to any one of paragraphs. 10-12, characterized in that the target resistance is determined after a few initial breaths of the user. 16. An aerosol generating system according to any one of paragraphs. 10-12, characterized in that during the implementation of several initial breaths of the user, only the first control mode is used, and tracking, and detecting a given condition, and registering resistance. 17. An aerosol generating system according to claim 15 or 16, characterized in that the target resistance is determined based on the average of the recorded resistances from several initial breaths of the user. 18. An aerosol generating system as claimed in claim 17, characterized in that when the user inhales after several initial breaths of the user, only the second control mode is used, and the target resistance is based on the average of the recorded resistances from several initial breaths of the user. 19. Controller for an aerosol generating system, wherein the controller is configured to carry out the method according to any one of paragraphs. 1-9. 20. A computer program that, when executed on a programmable controller for an aerosol generating system, causes the programmable controller to execute the method of any one of claims. 1-9.

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