RU2849871C2 - Method for calibrating an induction heating device, induction heating device and aerosol generating system - Google Patents

Abstract

FIELD: method for calibrating an induction heating device, induction heating device, and aerosol generating system.

SUBSTANCE: the method comprises obtaining a sequence of calibration values of the induction heating device for the aerosol generating system, wherein the sequence of calibration values is related to a calibration curve, smoothing the sequence of calibration values to obtain a sequence of smoothed calibration values, determining the first derivative of the sequence of smoothed calibration values, evaluating the maximum value of the first derivative of the sequence of smoothed calibration values, determining at least one of the aligned characteristic and the peak point value based on a first threshold associated with the evaluated maximum value of the first derivative, and operating the induction heating device in accordance with at least one of the determined aligned characteristic and peak point value.

EFFECT: temperature control to reduce the risk of overheating and ensure the smooth operation of the aerosol generating device.

14 cl, 10 dwg

Description

The present invention relates to an induction heating device for heating an aerosol-forming substrate. The present invention further relates to a method for calibrating the induction heating device.

Aerosol-generating devices may contain an electrically controlled heat source configured to heat the aerosol-forming substrate to produce the aerosol. For aerosol-generating devices, it is important to accurately monitor and regulate the temperature of the electrically controlled heat source to ensure optimal aerosol generation and delivery to the user. In particular, it is important to ensure that the electrically controlled heat source does not overheat the aerosol-forming substrate, as this can lead to combustion of the aerosol-forming substrate, resulting in the formation of undesirable compounds and an unpleasant taste and odor for the user.

It is desirable to provide an efficient and rapid method for calibrating the induction heating device, ensuring reliable temperature control in order to reduce the risk of overheating and ensure continued normal operation of the aerosol generating device.

WO 2020/223350 A1 (H05B 6/10, November 5, 2020) discloses a system for determining the characteristics of a current-collecting element that can be associated with an evaporation device. The system comprises an induction element and a control device. The control device is configured to determine a magnetic field associated with the induction element and to determine the characteristics of the current-collecting element based on the magnetic field.

The objective of the present invention is to provide an improved method and system for calibrating an induction heating device, ensuring reliable temperature control to reduce the risk of overheating and uninterrupted operation of the aerosol generating device.

This problem is solved by means of independent claims of the invention.

According to one embodiment of the present invention, a method for calibrating an induction heating device for an aerosol generating system is provided. The method includes obtaining a sequence of calibration values of the induction heating device for the aerosol generating system. The sequence of calibration values is associated with a calibration curve. The method further includes smoothing the sequence of calibration values to obtain a sequence of smoothed calibration values, determining the first derivative of the sequence of smoothed calibration values, estimating the maximum value of the first derivative of the sequence of smoothed calibration values; determining at least one of the smoothed characteristic and the peak point value based on a first threshold associated with the estimated maximum value of the first derivative; and operating the induction heating device in accordance with the determined at least one of the smoothed characteristic and the peak point value. The induction heating device may be a portable induction heating device. Alternatively, the induction heating device may be a part of a portable device.

By estimating the maximum value of the first derivative of a sequence of smoothed calibration values and determining at least one of the smoothed characteristic and the peak point value based on a first threshold associated with the estimated maximum value of the first derivative, and operating the induction heating device in accordance with the determined at least one of the smoothed characteristic and the peak point value, it is possible to quickly, reliably, and accurately determine the characteristic point or characteristic property of the calibration curve. By operating the induction heating device in accordance with the determined at least one of the smoothed characteristic and the peak point value, the characteristic point or characteristic property of the calibration curve can be used to prevent overheating of the device, thereby increasing user safety. For example, the formation of undesirable components when heating an aerosol-forming substrate above a critical temperature can be avoided.

The step of smoothing the sequence of calibration values and the step of determining the first derivative of the sequence of smoothed calibration values can be performed in a single calculation, which allows saving computing resources.

The step of estimating the maximum value of the first derivative of the sequence of smoothed calibration values may include comparing the value of the first derivative of the sequence of smoothed calibration values with a specified number of values of the first derivative of the sequence of smoothed calibration values. Alternatively, the value of the first derivative of the sequence of smoothed calibration values may be estimated as the maximum value if the average value of a specified number of previous values of the first derivative of the sequence of smoothed calibration values is higher than the value of the first derivative of the sequence of smoothed calibration values.

The first threshold may be a fraction of the maximum value of the first derivative of a sequence of smoothed calibration values. By determining at least one of the leveled characteristic and the peak point value based on the first threshold, which is a fraction of the maximum value of the first derivative of a sequence of smoothed calibration values, a reliable method for determining said at least one of the leveled characteristic and the peak point value is provided, since at least the leveled characteristic can be determined even though the calibration curve does not contain a maximum.

The method may include the step of terminating heating of the induction heating device when the first derivative of the sequence of smoothed calibration values increases again after the maximum value of the first derivative of the sequence of smoothed calibration values. The repeated increase of the first derivative of the sequence of smoothed calibration values after the maximum value of the first derivative of the sequence of smoothed calibration values may be determined when the average value of a specific number of successive values of the first derivative increases over time.

By stopping the heating of the induction heating device when the first derivative of the smoothed calibration value sequence increases again, a safe method is provided that provides protection against overheating.

The method may further comprise determining the type of the calibration curve by classifying the calibration curve and selecting, based on the determined type of the calibration curve, at least one parameter for calibration. The calibration curve may be classified based on the slope of the calibration curve. Alternatively or additionally, the calibration curve may be classified based on the time corresponding to the maximum of the first derivative.

This further increases the accuracy and reliability of the calibration process, as the parameters can be selected for a specific calibration curve.

The method may further include stopping heating of the induction heating device in response to determining at least one of the aligned characteristic and the peak point value. This provides an efficient and safe calibration method, as the method does not require heating beyond the peak point to determine the peak point.

According to one embodiment of the present invention, an induction heating device is provided for an aerosol generating system, wherein the induction heating device comprises a controller configured to receive a sequence of calibration values of the induction heating device, wherein the sequence of calibration values is associated with a calibration curve; smoothing the sequence of calibration values to obtain a sequence of smoothed calibration values; determining a first derivative of the sequence of smoothed calibration values; estimating a maximum value of the first derivative of the sequence of smoothed calibration values; and determining at least one of the smoothed characteristic and the peak point value based on a first threshold associated with the estimated maximum value of the first derivative. The induction heating device is operated in accordance with the determined at least one of the smoothed characteristic and the peak point value. The induction heating device may comprise an inductor configured to be inductively connected to a susceptor for heating an aerosol-forming substrate, and wherein the calibration values are associated with the susceptor. An induction heating device may comprise a power source for supplying a DC and DC supply voltage and an electronic power supply circuit connected to the power source. The electronic power supply circuit may comprise: a DC to AC converter; an inductor, wherein the inductor is connected to the DC to AC converter for generating an alternating magnetic field when excited by an alternating current from the DC to AC converter; and a controller, wherein the controller is configured to regulate the power supplied to the electronic power supply circuit to cause an increase in the temperature of the current collector. Obtaining a sequence of calibration values may include measuring the current associated with the electronic power supply circuit of the induction heating device.

This provides an improved induction heating device that can reliably and reliably determine at least one of a leveled characteristic and a peak point value for calibrating the induction heating device with respect to temperature without continuously measuring the temperature.

According to one embodiment of the present invention, an aerosol generating system is provided, comprising an induction heating device as described above and an aerosol generating article, wherein the aerosol generating article comprises an aerosol forming substrate and a current collector.

As used herein, the term "aerosol-generating device" refers to a device that interacts with an aerosol-forming substrate to generate an aerosol. The aerosol-generating device may interact with one or both of an aerosol-generating article containing the aerosol-forming substrate and a cartridge containing the aerosol-forming substrate. In some examples, the aerosol-generating device may heat the aerosol-forming substrate to facilitate the release of volatile compounds from the substrate. An electrically powered aerosol-generating device may include an atomizer, such as an electric heater, for heating the aerosol-forming substrate to form an aerosol.

For the purposes of this document, the term "aerosol-generating system" refers to the combination of an aerosol-generating device and an aerosol-generating substrate. When the aerosol-generating substrate forms part of an aerosol-generating article, the aerosol-generating system refers to the combination of the aerosol-generating device and the aerosol-generating article. In an aerosol-generating system, the aerosol-generating substrate and the aerosol-generating device interact to generate an aerosol.

For the purposes of this document, the term "aerosol-forming substrate" refers to a substrate capable of releasing volatile compounds that can form an aerosol. The volatile compounds can be released by heating or burning the aerosol-forming substrate. As an alternative to heating or burning, in some cases, the volatile compounds can be released through a chemical reaction or mechanical action, such as ultrasonication. The aerosol-forming substrate can be solid or liquid, or may contain both solid and liquid components. The aerosol-forming substrate can be part of an aerosol-generating article.

As used herein, the term "aerosol-generating article" refers to an article containing an aerosol-forming substrate capable of releasing volatile compounds that can form an aerosol. An aerosol-generating article may be disposable. An aerosol-generating article containing an aerosol-forming substrate containing tobacco may be referred to herein as a tobacco stick.

The aerosol-forming substrate may comprise nicotine. The aerosol-forming substrate may comprise tobacco, for example, it may comprise a tobacco-containing material containing volatile tobacco flavor compounds that are released from the aerosol-forming substrate upon heating. In preferred embodiments, the aerosol-forming substrate may comprise homogenized tobacco material, such as leaf tobacco. The aerosol-forming substrate may comprise 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. The aerosol-forming substrate may comprise a non-tobacco material. The aerosol-forming substrate may further comprise an aerosol-forming agent. Examples of suitable aerosol-forming agents include glycerin and propylene glycol.

In the context of this document, the term "current collector" refers to an element containing a material capable of converting magnetic field energy into heat. When the current collector is exposed to an alternating magnetic field, the current collector heats up. Heating of the current collector may be the result of at least one of hysteresis losses and eddy currents induced in the current collector, depending on the electrical and magnetic properties of the current collector material.

In the context of this document, with respect to an aerosol-generating device, the terms "upstream" and "front," as well as "downstream" and "rear," are used to describe the relative positions of components or portions of components of an aerosol-generating device with respect to the direction in which air flows through the aerosol-generating device during use. Aerosol-generating devices according to the present invention include a proximal end through which the aerosol exits the device during use. The proximal end of an aerosol-generating device may also be referred to as the mouthpiece end or the downstream end. The mouthpiece end is located downstream of the distal end. The distal end of an aerosol-generating article may also be referred to as the upstream end. Components or portions of components of an aerosol generating device may be described as being upstream or downstream relative to one another based on their relative positions with respect to the airflow path of the aerosol generating device.

In the context of this document, with respect to an aerosol-generating article, the terms "upstream" and "front," as well as "downstream" and "rear," are used to describe the relative positions of components or portions of components of the aerosol-generating article with respect to the direction in which air flows through the aerosol-generating article during use. The aerosol-generating article of the present invention includes a proximal end through which the aerosol exits the article during use. The proximal end of the aerosol-generating article may also be referred to as the mouthpiece end or the downstream end. The mouthpiece end is located downstream of the distal end. The distal end of the aerosol-generating article may also be referred to as the upstream end. Components or portions of components of an aerosol-generating article may be described as upstream or downstream relative to one another based on their relative positions between the proximal end of the aerosol-generating article and the distal end of the aerosol-generating article. The forward side of a component or portion of a component of an aerosol-generating article is the portion at the end closest to the upstream end of the aerosol-generating article. The rear side of a component or portion of a component of an aerosol-generating article is the portion at the end closest to the downstream end of the aerosol-generating article.

In the context of this document, the term "inductive coupling" refers to the heating of a current collector when an alternating magnetic field passes through it. Heating can be caused by the generation of eddy currents in the current collector. Heating can also be caused by magnetic hysteresis losses.

The present invention is defined in the claims. However, a non-exhaustive list of non-limiting examples is provided below. Any one or more of the features of these examples may be combined with any one or more features of another example, embodiment or aspect described herein. Example Ex1: A method of calibrating an induction heating device for an aerosol generating system, wherein the method comprises obtaining a sequence of calibration values of the induction heating device for the aerosol generating system, wherein the sequence of calibration values is associated with a calibration curve; smoothing the sequence of calibration values to obtain a sequence of smoothed calibration values; determining a first derivative of the sequence of smoothed calibration values; estimating a maximum value of the first derivative of the sequence of smoothed calibration values; determining at least one of a smoothed characteristic and a peak point value based on a first threshold associated with the estimated maximum value of the first derivative; and operating the induction heating device in accordance with the determined at least one of the smoothed characteristic and the peak point value.

Example Ex2: The method according to example Ex1, wherein the smoothing comprises convolving a sequence of calibration values with at least one Gaussian kernel.

Example Ex3: The method according to example Ex2, wherein at least one Gaussian kernel comprises half of a Gaussian kernel.

Example Ex4: The method according to example Ex1 or Ex2, wherein at least one Gaussian kernel comprises a symmetric Gaussian kernel.

Example Ex5: The method of example Ex1, wherein the smoothing comprises convolving a sequence of calibration values with a half Gaussian kernel and a symmetric Gaussian kernel, wherein the half Gaussian kernel and the symmetric Gaussian kernel are associated with different standard deviations.

Example Ex6: The method according to any of the examples Ex1 to Ex5, wherein smoothing the sequence of calibration values and determining the first derivative of the sequence of smoothed calibration values are performed in a single calculation.

Example Ex7: The method according to any of examples Ex1-Ex6, wherein estimating the maximum value of the first derivative of the sequence of smoothed calibration values comprises comparing the value of the first derivative of the sequence of smoothed calibration values with a given number of values of the first derivative of the sequence of smoothed calibration values.

Example Ex8: The method according to any of examples Ex1-Ex6, wherein the value of the first derivative of the sequence of smoothed calibration values is estimated as the maximum value if the average value of a given number of previous values of the first derivative of the sequence of smoothed calibration values is higher than the value of the first derivative of the sequence of smoothed calibration values.

Example Ex9: The method according to any one of examples Ex1 to Ex8, wherein the first threshold is a fraction of the maximum value of the first derivative of the sequence of smoothed calibration values.

Example Ex10: The method according to any one of examples Ex1 to Ex9, further comprising stopping heating of the induction heating device when the first derivative of the sequence of smoothed calibration values increases again after the maximum value of the first derivative of the sequence of smoothed calibration values.

Example Ex11: The method according to example Ex10, in which the repeated increase of the first derivative of the sequence of smoothed calibration values after the maximum value of the first derivative of the sequence of smoothed calibration values is determined if the average value of a specific number of successive values of the first derivative increases over time.

Example Ex12: The method according to any of examples Ex1-Ex1l, further comprising determining the type of calibration curve by classifying the calibration curve and selecting, based on the determined type of calibration curve, at least one parameter for calibration.

Example Ex13: The method according to example Ex12, wherein the calibration curve is classified based on the slope of the calibration curve.

Example Ex14: The method according to any of examples Ex12 and Ex13, wherein the type is related to one of the recalibration and the calibration curve, and the slope of one of the recalibration curve and the calibration curve.

Example Ex15: The method according to any of examples Ex12 and Ex14, wherein the type of the calibration curve is determined based on a second threshold associated with the estimated maximum value of the first derivative of the sequence of smoothed calibration values.

Example Ex16: The method according to any of examples Ex12 and Ex15, wherein the first parameter of the at least one parameter indicates a first threshold for the step of determining at least one of the aligned characteristic and the peak point value.

Example Ex17: The method according to any of examples Ex12 to Ex16, wherein the second parameter of the at least one parameter indicates smoothing of the sequence of calibration values.

Example Ex18: The method according to any of the examples Ex12-Ex17, wherein the third parameter of the at least one parameter indicates the number of consecutive values of the first derivative of the sequence of smoothed calibration values used for the step of estimating the maximum value of the first derivative.

Example Ex19: The method according to one of the examples Ex12-Ex18, wherein the fourth parameter of the at least one parameter indicates the number of successive values of the first derivative of the sequence of smoothed calibration values used for the step of determining at least one of the smoothed characteristic and the peak point value.

Example Ex20: The method according to any of the examples Ex12 to Ex19, wherein the fifth parameter of at least one parameter indicates the number of values of the first derivative of the sequence of smoothed calibration values used for the step of determining the repeated increase of the first derivative of the sequence of smoothed calibration values after the maximum value of the first derivative of the sequence of smoothed calibration values.

Example Ex21: The method according to any one of examples Ex12 to Ex20, wherein the second threshold is a fraction of the maximum value of the first derivative of the sequence of smoothed calibration values.

Example Ex22: The method according to example Ex1, wherein operating the induction heating device in accordance with the determined at least one of the leveled characteristic and the peak point value includes maintaining a temperature associated with the aerosol generating system below a specific temperature based on the determined at least one of the leveled characteristic and the peak point value.

Example Ex23: The method according to any one of examples Ex1 to Ex22, further comprising stopping heating of the induction heating device in response to determining at least one of the leveled characteristic and the peak point value.

Example Ex24: The method according to any of the examples Ex1 to Ex23, wherein the sequence of calibration values is obtained during a calibration phase of the induction heating device.

Example Ex25: The method according to any of the examples Ex1 to Ex23, wherein the sequence of calibration values is obtained during recalibration of the induction heating device.

Example Ex26: An induction heating device for an aerosol generating system, wherein the induction heating device comprises a controller configured to receive a sequence of calibration values of the induction heating device, wherein the sequence of calibration values is associated with a calibration curve, smooth the sequence of calibration values to obtain a sequence of smoothed calibration values, determine a first derivative of the sequence of smoothed calibration values, estimate a maximum value of the first derivative of the sequence of smoothed calibration values, and determine at least one of the smoothed characteristic and the peak point value based on a first threshold associated with the estimated maximum value of the first derivative, wherein the induction heating device is operated in accordance with the determined at least one of the smoothed characteristic and the peak point value.

Example Ex27: An induction heating device according to example Ex26, wherein the induction heating device comprises an inductor configured to be inductively coupled to a current collector for heating an aerosol-forming substrate, and wherein the calibration values are associated with the current collector.

Example Ex28: An induction heating device according to example Ex27, wherein the induction heating device comprises a power source for supplying a DC supply voltage and a DC current; an electronic power supply circuit connected to the power source, wherein the electronic power supply circuit comprises: a DC to AC converter; an inductor, wherein the inductor is connected to the DC to AC converter for generating an alternating magnetic field when excited by an AC current from the DC to AC converter; and a controller, wherein the controller is configured to regulate the power supplied to the electronic power supply circuit to cause an increase in the temperature of the current collector.

Example Ex29: An induction heating device according to example Ex28, wherein obtaining a sequence of calibration values comprises measuring a current associated with an electronic power supply circuit of the induction heating device.

Example Ex30: An induction heating device according to any of examples Ex26 to Ex29, wherein at least one of the levelled characteristic and the peak point value corresponds to a known temperature.

Example Ex31: An induction heating device according to any of examples Ex27 to Ex30, wherein the sequence of calibration values comprises a sequence of conductivity values, wherein the conductivity value of the sequence of conductivity values is related to a calibration temperature of the current collector.

Example Ex32: An induction heating device according to any of examples Ex27 to Ex31, wherein the sequence of calibration values comprises a sequence of resistance values, wherein the resistance value of the sequence of resistance values is related to a calibration temperature of the current collector.

Example Ex33. An induction heating device according to any of the examples Ex27-Ex32, wherein at least one of the leveled characteristic and the peak point value corresponds to the Curie temperature of the current collector material.

Example Ex34: An induction heating device according to any of examples Ex27 to Ex33, wherein the current collector comprises a first current collector material having a first Curie temperature and a second current collector material having a second Curie temperature, wherein the second Curie temperature is lower than the first Curie temperature, and wherein at least one of the leveled characteristic and the peak point value corresponds to the second Curie temperature of the second current collector material.

Example Ex35: An induction heating device according to any one of examples Ex26-Ex34, wherein the controller is configured to determine a valley point of a sequence of smoothed calibration values and calibrate the induction heating device based on the determined valley point and the determined at least one of the smoothed characteristic and the peak point value.

Example Ex36: An induction heating device according to example Ex35, wherein the valley point corresponds to a known temperature.

Example Ex37: An induction heating device according to any of examples Ex26 to Ex36, wherein the calibration is performed periodically as a recalibration during use of the induction heating device.

Example Ex38: An induction heating device according to any of examples Ex26 and Ex37, further comprising: a current sensor configured to measure, on the input side of the DC/AC converter, the DC current consumed from the power source; and a voltage sensor configured to measure, on the input side of the DC/AC converter, the DC supply voltage of the power source, wherein the sequence of calibration values comprises a sequence of conductivity values or a sequence of resistance values, and wherein the conductivity values or the resistance values associated with the current collector are determined from the DC supply voltage of the power source and the DC current consumed from the power source.

Example Ex39: An induction heating device according to example Ex26, wherein the calibration values include conductivity values, and wherein the controller is configured to regulate the power supplied to the electronic circuit of the power supply to maintain the conductivity value associated with the current collector below at least one of the flattened characteristic and the peak point value.

Example Ex40: An aerosol generating system comprising an induction heating device according to any one of paragraphs 26 to 39 and an aerosol generating article, wherein the aerosol generating article comprises an aerosol forming substrate and a susceptor.

The examples will now be further described with reference to figures, where:

Fig. 1 shows a schematic cross-sectional view of an aerosol generating article;

Fig. 2A is a schematic cross-sectional view of an aerosol generating device for use with the aerosol generating article illustrated in Fig. 1;

Fig. 2B is a schematic cross-sectional view of an aerosol generating device in engagement with the aerosol generating article illustrated in Fig. 1;

Fig. 3 is a schematic diagram showing the induction heating device of the aerosol generating device described in relation to Fig. 2;

Fig. 4 is a schematic diagram showing the electronic components of the induction heating device described in relation to Fig. 3;

Fig. 5 shows a schematic representation of the LC circuit inductor of the load of the induction heating device described in relation to Fig. 4;

Fig. 6 is a graph of direct current versus time illustrating remotely detectable current changes that occur when a current-collecting material undergoes a phase transition associated with its Curie point;

Fig. 7 shows the temperature profile of the current collector during operation of the aerosol generating device;

Fig. 8 shows a block diagram of a method for calibrating an induction heating device for an aerosol generating system;

Fig. 9A shows a classification tree that can be trained on recalibration test curves;

Fig. 9B shows a classification tree that can be trained on test calibration curves; and

Fig. 10 shows an example of a recalibration curve.

Fig. 1 shows a schematic side sectional view of an aerosol-generating article 100. The aerosol-generating article 100 comprises a rod of aerosol-generating substrate 110 and a downstream section 115 in a downstream position relative to the rod of aerosol-generating substrate 110. The aerosol-generating article 100 comprises an upstream section 150 in a upstream position relative to the rod of aerosol-generating substrate. Thus, the aerosol-generating article 100 extends from an upstream or distal end 180 to a downstream or mouthpiece end 170. In use, air is drawn through the aerosol-generating article 100 by the user from the distal end 180 to the mouthpiece end 170.

The downstream section 115 comprises a support member 120 located immediately downstream of the aerosol-forming substrate rod, wherein the support member 120 is in longitudinal alignment with the rod 110. The upstream end of the support member 120 is adjacent to the downstream end of the aerosol-forming substrate rod 110. In addition, the downstream section 115 comprises an aerosol cooling element 130 located immediately downstream of the support element 120, wherein the aerosol cooling element 130 is in longitudinal alignment with the rod 110 and the support element 120. The upstream end of the aerosol cooling element 130 is adjacent to the downstream end of the support element 120. In use, volatiles released from the aerosol-forming substrate 110 pass along the aerosol cooling element 130 toward the mouthpiece end 170 of the aerosol-generating article 100. The volatiles can be cooled within the aerosol cooling element 130 to form an aerosol that is inhaled by the user.

The support element 120 comprises a first hollow tubular segment 125. The first hollow tubular segment 125 is provided in the form of a hollow cylindrical tube made of cellulose acetate. The first hollow tubular segment 125 forms an internal cavity 145 that extends the entire distance from the upstream end 165 of the first hollow tubular segment 125 to the downstream end 175 of the first hollow tubular segment 125.

The aerosol cooling element 130 comprises a second hollow tubular segment 135. The second hollow tubular segment 135 is provided in the form of a hollow cylindrical tube made of cellulose acetate. The second hollow tubular segment 135 forms an internal cavity 155 that extends over the entire distance from the upstream end 185 of the second hollow tubular segment 135 to the downstream end 195 of the second hollow tubular segment 135. In addition, a ventilation zone (not shown) is provided at a location along the second hollow tubular segment 135. The ventilation level of the aerosol generating article 10 is approximately 25 percent.

The downstream section 115 further comprises a mouthpiece 140 located immediately downstream of the aerosol cooling element 130. As shown in the image in Fig. 1, the upstream end of the mouthpiece 140 adjoins the downstream end 195 of the aerosol cooling element 130. The mouthpiece 140 is provided in the form of a cylindrical rod made of low-density cellulose acetate.

The aerosol-generating article 100 further comprises an elongated current collector 160 within the rod of the aerosol-generating substrate 110. In more detail, the current collector 160 is located substantially in the longitudinal direction within the aerosol-generating substrate 110 in such a way as to be approximately parallel to the longitudinal direction of the rod 110. As shown in the image of Fig. 1, the current collector 160 is located in a radially central position within the rod and extends substantially along the longitudinal axis of the rod 110.

The current collector 160 extends the entire distance from the upstream end to the downstream end of the aerosol-forming substrate rod 110. In fact, the current collector 160 has substantially the same length as the rod of the aerosol-forming substrate 110. The current collector 160 is positioned in thermal contact with the aerosol-forming substrate 110, causing the aerosol-forming substrate 110 to be heated by the current collector 160 as the current collector 160 heats up.

The upstream section 150 comprises an upstream element 190 positioned immediately upstream of the aerosol-forming substrate rod 110, wherein the upstream element 190 is in longitudinal alignment with the rod 110. The downstream end of the upstream element 190 is adjacent to the upstream end of the aerosol-forming substrate rod. This advantageously prevents the current collector 160 from shifting. In addition, this ensures that the consumer cannot accidentally touch the heated current collector 160 after use. The upstream element 190 is provided in the form of a cylindrical rod of cellulose acetate, which is surrounded by a rigid wrapper.

Current collector 160 comprises at least two different materials. Current collector 160 comprises at least two layers: a first layer of a first current-receiving material located in physical contact with a second layer of a second current-receiving material. Each of the first current-receiving material and the second current-receiving material may have a Curie temperature. In this case, the Curie temperature of the second current-receiving material is lower than the Curie temperature of the first current-receiving material. The first material may not have a Curie temperature. The first current-receiving material may be aluminum, iron, or stainless steel. The second current-receiving material may be nickel or a nickel alloy.

Current collector 160 may be formed by electrolytically depositing at least one portion of a second current-collecting material onto a strip of a first current-collecting material. The current collector may be formed by applying a strip of the second current-collecting material onto a strip of the first current-collecting material.

The aerosol-generating article 100 shown in Fig. 1 is designed to cooperate with an aerosol-generating device, such as the aerosol-generating device 200 shown in Fig. 2A, to produce an aerosol. The aerosol-generating device 200 comprises a body 210 having a cavity 220 configured to receive the aerosol-generating article 100, and an induction heating device 230 configured to heat the aerosol-generating article 100 to produce an aerosol. Fig. 2B illustrates the aerosol-generating device 200 when the aerosol-generating article 100 is inserted into the cavity 220. The aerosol-generating device 200 may optionally further comprise a puff detector located within or near the cavity 220 (not shown) to detect puffs. The puff detector is located within or near cavity 200, whereby the puff detector is positioned along the airflow path when the user takes a puff. The puff detector may include one or more temperature sensors for detecting a change in the airflow temperature in cavity 220, indicating that the user is taking a puff. Additionally or alternatively, the puff detector may include a pressure sensor for detecting a decrease in airflow pressure in cavity 220, indicating that the user is taking a puff.

The induction heating device 230 is schematically depicted in Fig. 3. The induction heating device 230 comprises a DC power source 310 and a heating device 320 (also referred to as a power supply electronic circuit). The heating device comprises a controller 330, a DC-to-AC converter 340, a matching circuit 350, and an inductor 240.

The DC power source 310 is configured to supply DC power to the heating device 320. In particular, the DC power source 310 is configured to supply DC power voltage ( _VDC ) and DC current ( _IDC ) to the DC-to-AC converter 340. Preferably, the power source 310 is a battery, such as a lithium iron phosphate battery. Alternatively, the power source 310 may be another type of charge storage device, such as a capacitor. The power source 310 may require recharging. For example, the power source 310 may have a capacity sufficient to enable continuous aerosol generation for a period equal to approximately six minutes, or for a period multiple of six minutes. In another example, the power source 310 may have a capacity sufficient to enable a predetermined number of puffs or individual activations of the heating device.

The DC-to-AC converter 340 is configured to supply the inductor 240 with high-frequency alternating current. In the context of this document, the term "high-frequency alternating current" means alternating current with a frequency of approximately 500 kilohertz to approximately 30 megahertz. The high-frequency alternating current may have a frequency of approximately 1 megahertz to approximately 30 megahertz, for example, from approximately 1 megahertz to approximately 10 megahertz, or, for example, from approximately 5 megahertz to approximately 8 megahertz.

Fig. 4 schematically shows the electrical components of the induction heating device 230, in particular the DC to AC converter 340. The DC to AC converter 340 preferably comprises a class E power amplifier. The class E power amplifier comprises a transistor switch 410 comprising a field effect transistor 420, for example a field effect transistor with a metal-oxide-semiconductor structure, a transistor switch power supply circuit, indicated by an arrow 430, for supplying a switching signal (gate-source voltage) to the field effect transistor 420, and an LC load circuit 440 comprising a shunt capacitor C1 and a series connection of a capacitor C2 and an inductor L2 corresponding to the inductor 240. In addition, a DC power supply 310 is shown, comprising a choke L1, for supplying a DC supply voltage V _DC , with a DC current I _DC , consumed from the DC power supply 310, during operation. The ohmic resistance R representing the total ohmic load 450, which is the sum of the ohmic resistance R of the inductor _coil L2 and the ohmic resistance R _{of the load} of the current collector 160, is shown in more detail in Fig. 5.

Although DC-to-AC converter 340 is shown as comprising a Class E power amplifier, it should be understood that DC-to-AC converter 340 may utilize any suitable circuit that converts DC to AC. For example, DC-to-AC converter 340 may comprise a Class D power amplifier comprising two transistor switches. As another example, DC-to-AC converter 340 may comprise a full-bridge inverting power amplifier with four switching transistors operating in pairs.

Returning to Fig. 3, inductor 240 may receive alternating current from DC-to-AC converter 340 through matching circuit 350 for optimal adaptation to the load, but matching circuit 350 is not critical. Matching circuit 350 may include a small matching transformer. Matching circuit 350 may improve the efficiency of power transfer between DC-to-AC converter 340 and inductor 240.

As shown in Fig. 2A, the inductor 240 is located near the distal portion 225 of the cavity 220 of the aerosol generating device 200. Accordingly, the high-frequency alternating current supplied to the inductor 240 during operation of the aerosol generating device 200 causes the inductor 240 to generate a high-frequency alternating magnetic field in the distal portion 225 of the aerosol generating device 200. The alternating magnetic field preferably has a frequency of 1 to 30 megahertz, preferably 2 to 10 megahertz, for example 5 to 7 megahertz. As can be seen in Fig. 2 V, when the aerosol-generating article 100 is introduced into the cavity 200, the aerosol-forming substrate 110 of the aerosol-generating article 100 is located near the inductor 240, so that the susceptor 160 of the aerosol-generating article 100 is located within this alternating magnetic field. When the alternating magnetic field penetrates the susceptor 160, the alternating magnetic field causes the susceptor 160 to heat up. For example, eddy currents are generated in the susceptor 160, which heats up as a result. Additional heating is provided by magnetic hysteresis losses inside the susceptor 160. The heated susceptor 160 heats the aerosol-forming substrate 110 of the aerosol-generating article 100 to a sufficient temperature for the formation of an aerosol. The aerosol is drawn further downstream through the aerosol generating article 100 and inhaled by the user.

Controller 330 may be a microcontroller, preferably a programmable microcontroller. Controller 330 is programmed to regulate the power supply from DC source 310 to induction heating device 320 to regulate the temperature of susceptor 160.

Fig. 6 illustrates the relationship between the direct current I _DC drawn from the power source 310 and time as the temperature of the current collector 160 (indicated by the dotted line) increases. More specifically, Fig. 6 depicts remotely detectable changes in the direct current that occur when the current collector material undergoes a phase transition associated with its Curie point. The direct current I _DC drawn from the power source 310 is measured at the input side of the DC-to-AC converter 340. For illustrative purposes, it can be assumed that the voltage V _DC of the power source 310 remains approximately constant.

As the current collector 160 is inductively heated, the apparent resistance of the current collector 160 increases. This increase in resistance is observed as a decrease in the direct current I _DC drawn from the power source 310, which at a constant voltage decreases as the temperature of the current collector 160 increases. The high-frequency alternating magnetic field provided by the inductor 240 induces eddy currents in the immediate vicinity of the surface of the current collector, an effect known as the skin effect. The resistance of the current collector 160 depends partly on the electrical resistance of the first current collector material, the specific resistance of the second current collector material, and partly on the depth of the surface layer in each material accessible to the induced eddy currents, and the specific resistance, in turn, depends on the temperature.

As the second current-collecting material reaches its Curie temperature, it loses its magnetic properties. This causes an increase in the surface layer accessible to eddy currents in the second current-collecting material, which causes a decrease in the apparent resistance of current collector 160. The result is a temporary increase in the detectable direct current I _DC . Then, as the layer depth of the second current-collecting material begins to increase, the resistance begins to decrease. This is visible as a trough (local minimum) in Fig. 6.

As heating continues, the current continues to increase until the maximum layer depth is reached, which coincides with the point at which the second current-collecting material has lost its spontaneous magnetic properties. This point is called the Curie temperature and is visible as a rise (local maximum) in Fig. 6. At this point, the second current-collecting material has undergone a phase transition from a ferromagnetic or ferrimagnetic state to a paramagnetic state. At this point, current collector 160 is at a known temperature (the Curie temperature, which is the internal temperature dependent on the specific material).

If the inductor 240 continues to generate an alternating magnetic field (i.e., power to the DC/AC converter 340 is not interrupted) after the Curie temperature is reached, the eddy currents generated in the current collector 160 will collide with the resistance of the current collector 160, causing Joule heating in the current collector 160 to continue, and thus the resistance will increase again (the resistance will have a polynomial dependence on temperature, which for most metallic current collector materials can be approximated by a third-degree polynomial dependence for our purposes), and the current will again begin to drop as long as the inductor 240 continues to supply power to the current collector 160.

Therefore, the second current-collecting material undergoes a reversible phase transition when heated in the (known) temperature range between the trough and the peak shown in Fig. 6. As can be seen from Fig. 6, the apparent resistance of the current collector 160, and hence the beginning and end of the phase transition, can be remotely detected by monitoring the direct current I _DC drawn from the power supply 310. Alternatively, the apparent resistance of the current collector 160, and hence the beginning and end of the phase transition, can be remotely detected by monitoring the conductivity value (where conductivity is defined as the ratio of the direct current I _DC to the direct current supply voltage V _DC ) or the resistance value (where resistance is defined as the ratio of the direct current supply voltage V _DC to the direct current I _DC ). At least the direct current I _DC drawn from the power supply 310 is monitored by the controller 330. Although the direct current supply voltage V _DC is known, both the direct current I _DC drawn from the power supply 310 and the direct current supply voltage V _DC are preferably monitored. The direct current I _DC , the conductance value, and the resistance value may be referred to as parameters of the power supply.

As the current collector 160 heats up, the first critical point (corresponding to a local minimum for current and a local maximum for resistance) marks the beginning of the phase transition. Then, as the current collector heats up further, the second critical point (corresponding to a local maximum for current and a local minimum for resistance) marks the end of the phase transition.

In addition, as can be seen from Fig. 6, the apparent resistance of the current collector 160 (and, accordingly, the current I _DC , consumed from the power source 310) can change along with the temperature of the current collector 160 in a strictly constant ratio in certain ranges of the temperature of the current collector 160, for example, between a trough and a peak. A strictly constant ratio allows for an unambiguous determination of the temperature of the current collector 160 based on the determination of the apparent resistance (R) or apparent conductivity (1/R). This is due to the fact that each determined value of the apparent resistance is characteristic of only one single temperature value, therefore, there is no ambiguity in the ratio. The constant ratio of the temperature of the current collector 160 and the apparent resistance in the temperature range in which the second current collector material undergoes a reversible phase transition makes it possible to determine and control the temperature of the current collector 160 and, thus, to determine and control the temperature of the substrate 110 forming the aerosol.

The controller 330 regulates the power supply to the heating device 320 based on the power supply parameter. The heating device 320 may comprise a current sensor (not shown) for measuring the direct current I _DC . The heating device may further comprise a voltage sensor (not shown) for measuring the direct current supply voltage V _DC . The current sensor and the voltage sensor are located on the input side of the DC-to-AC converter 340. The direct current I _DC and, optionally, the direct current supply voltage V _DC are fed via feedback channels to the controller 330 for regulating the further supply of the alternating current P _AC to the inductor 240.

The controller 330 may regulate the temperature of the current collector 160 by maintaining the measured value of the power supply parameter at a target value corresponding to the target operating temperature of the current collector 160. The controller 330 may use any suitable control loop to maintain the measured parameter of the power supply at the target value, for example, using a proportional-integral-derivative control loop.

Furthermore, the controller 330 can maintain the temperature of the current collector 160 below a predetermined threshold temperature by maintaining the measured conductivity or current value below a predetermined conductivity threshold or by maintaining the measured resistance value above a predetermined resistance threshold. The predetermined threshold temperature is selected to prevent overheating of the aerosol-generating substrate. If the measured power supply parameter indicates that the temperature of the current collector exceeds the predetermined threshold temperature, the controller 330 is programmed to switch to a safe mode. In the safe mode, the controller 330 is configured to perform one or more actions, such as generating an alarm that (visually and additionally or alternatively in the form of an audio signal) provides the user with an overheating warning, turning off the aerosol-generating device, and preventing further use of the aerosol-generating device for a predetermined period of time.

In order to take advantage of the strictly constant relationship between the apparent resistance (or apparent conductivity) of the current collector 160 and the temperature of the current collector 160 during user control for generating an aerosol, the power supply parameter measured at the input side of the DC/AC converter 340 is maintained between a first calibration value corresponding to a first calibration temperature and a second calibration value corresponding to a second calibration temperature. The second calibration temperature is the Curie temperature of the second current collector material (a rise in the current graph in Fig. 6). The first calibration temperature is a temperature greater than or equal to the temperature of the current collector, at which the layer thickness of the second current collector material begins to increase, which leads to a temporary decrease in resistance (a trough in the current graph in Fig. 6). Thus, the first calibration temperature is a temperature greater than or equal to the temperature at the maximum permeability of the second current collector material. The first calibration temperature is at least 50 degrees Celsius lower than the second calibration temperature. At least the second calibration value can be determined by calibrating the current collector 160, as will be described in more detail below. The first calibration value and the second calibration value can be stored as calibration values in the memory of the controller 330.

Since the power supply parameter will have a polynomial dependence on temperature, the power supply parameter will behave nonlinearly as a function of temperature. However, the first and second calibration values are selected such that this dependence can be approximated as linear between the first and second calibration values, since the difference between the first and second calibration values is small, and the first and second calibration values are at the upper end of the operating temperature range. Therefore, to bring the temperature to the target operating temperature, the power supply parameter is adjusted according to the first and second calibration values using linear equations.

For example, if the first and second calibration values are conductivity values, the target conductivity value corresponding to the target operating temperature can be specified using:

G _Target = G _Lower + (x×ΔG),

where ΔG is the difference between the first conductivity value and the second conductivity value, and x is the percentage of ΔG.

Controller 330 can regulate the power supply to heating device 320 by adjusting the duty cycle of switching transistor 410 of DC/AC converter 340. For example, during heating, DC/AC converter 340 continuously generates alternating current, which heats current collector 160, and simultaneously, direct current I _DC and optionally DC supply voltage V _DC can be measured, preferably every millisecond for 100 milliseconds.

For example, if the conductivity or current is monitored by the controller 330 to adjust the temperature of the current collector, then when the conductivity or current reaches or exceeds the value corresponding to the target operating temperature for adjusting the temperature of the current collector, the duty cycle of the switching transistor 410 is reduced. If the resistance is monitored by the controller 330 to adjust the temperature of the current collector, then when the resistance reaches or falls below the value corresponding to the target operating temperature, the duty cycle of the switching transistor 410 is reduced. For example, the duty cycle of the switching transistor 410 can be reduced to approximately 10%. In other words, the switching transistor 410 can be switched to a mode in which it generates pulses only every 10 milliseconds for 1 millisecond. During this 1 millisecond, in the on state (conducting state) of the switching transistor 410, the values of the _DC supply voltage VDC and the _DC current IDC are measured, and the conductivity is determined. When the conductivity decreases (or the resistance increases), indicating that the temperature of the current collector 160 is below the target operating temperature, a pulse train at the selected excitation frequency for the system is again applied to the gate of the transistor 410.

Power may be supplied by controller 330 to inductor 240 in the form of a series of sequential electric current pulses. Specifically, power may be supplied to inductor 240 via a series of pulses, each separated by a time interval. A series of sequential pulses may comprise two or more heating pulses and one or more probe pulses between successive heating pulses. The heating pulses have an intensity sufficient to heat current collector 160. The probe pulses are isolated power pulses of an intensity sufficient not to heat current collector 160, but rather to obtain feedback on the power supply parameter and subsequently on the change (decrease) in current collector temperature. The controller 330 may regulate the power supply by regulating the duration of the time interval between successive power heating pulses supplied by the DC power supply to the inductor 240. Additionally or alternatively, the controller 330 may regulate the power supply by regulating the duration (in other words, the length) of each of the successive power heating pulses supplied by the DC power supply to the inductor 240.

The controller 330 is programmed to perform a calibration process to obtain calibration values at which the power supply parameter is measured at known temperatures of the current collector 160. The known temperatures of the current collector may be a first calibration temperature corresponding to a first calibration value, and a second calibration temperature corresponding to a second calibration value. The calibration process is performed each time the user operates the aerosol-generating device 200. For example, the controller 330 may be configured to enter a calibration mode to perform the calibration process when the user turns on the aerosol-generating device. The controller 330 may be programmed to enter the calibration mode each time the user inserts the aerosol-generating article 100 into the aerosol-generating device 200. Thus, the calibration process is performed during the first heating phase of the aerosol generating device prior to the user operating the aerosol generating device 200 to generate an aerosol.

During the calibration process, the controller 330 controls the DC/AC converter 340 to continuously or continuously supply power to the inductor 240 to heat the current collector 160. The controller 330 monitors the power supply parameter by measuring the current I _DC consumed by the power supply and, optionally, the voltage V _DC of the power supply. As discussed above with respect to Fig. 6, as the current collector 160 heats up, the measured current decreases until the first critical point is reached and the current begins to increase. This first critical point corresponds to the local minimum value of conductivity or current (local maximum value of resistance). The controller 330 can record the power supply parameter at the first critical point as the first calibration value.

The conductivity or resistance values can be determined based on the measured current I _DC and the measured voltage V _DC . Alternatively, it can be assumed that the voltage V _DC of the power supply, which is a known property of the power source 310, is approximately constant. The temperature of the current collector 160 at the first calibration value is called the first calibration temperature. Preferably, the first calibration temperature is from 150 degrees Celsius to 350 degrees Celsius. More preferably, when the aerosol-forming substrate 110 contains tobacco, the first calibration temperature is 320 degrees Celsius. The first calibration temperature is at least 50 degrees Celsius lower than the second calibration temperature.

As controller 330 continues to regulate the power supplied by DC/AC converter 340 to inductor 240, controller 330 continues to monitor the power supply parameter until the second critical point is reached. The second critical point corresponds to the maximum current (corresponding to the Curie temperature of the second current-sensing material) before the measured current begins to decrease. This critical point corresponds to the local maximum conductivity or current (the local minimum resistance). Controller 330 records the power supply parameter value at the critical point as the second calibration value. The temperature of current-sensing material 160 at the second calibration value is called the second calibration temperature. Preferably, the second calibration temperature is between 200 degrees Celsius and 400 degrees Celsius. When the maximum value is detected, the controller 330 controls the DC-to-AC converter 340 to interrupt the power supply to the inductor 240, which results in a decrease in the temperature of the current collector 160 and a corresponding decrease in the measured current.

Due to the shape of the graph, this process of continuously heating the current collector 160 to obtain the first calibration value and the second calibration value can be repeated at least once during the calibration mode. After interrupting the power supply to the inductor 240, the controller 330 continues to monitor the power supply parameter until the third critical point is observed. The third critical point corresponds to the second minimum conductivity or current value (the second maximum resistance value). When the third critical point is detected, the controller 330 controls the DC/AC converter 340 to continuously supply power to the inductor 240 until the fourth critical point is observed in the monitored power supply parameter. The fourth critical point corresponds to the second maximum conductivity or current value (the second minimum resistance value). Controller 330 stores the power supply parameter value measured at the third critical point as the first calibration value, and the power supply parameter value measured at the fourth critical point as the second calibration value. Repeated measurement of the critical points corresponding to the minimum and maximum measured current significantly improves subsequent temperature regulation during user control of the aerosol generating device. Preferably, controller 330 regulates the power supply based on the power supply parameter values obtained from the second maximum value and the second minimum value, which is more reliable since the heat will have more time to distribute within the aerosol-forming substrate 110 and the current collector 160.

Additionally, during the first heating phase, to further improve the reliability of the calibration process, controller 310 may be optionally programmed to perform a preheating process prior to the calibration process. For example, if aerosol-forming substrate 110 is particularly dry or under similar conditions, calibration may be performed before heat has diffused within aerosol-forming substrate 110, reducing the reliability of the calibration values. If aerosol-forming substrate 110 was wet, susceptor 160 requires more time to reach the valley temperature (due to the water content of substrate 110).

To perform the preheating process, the controller 330 is configured to continuously supply power to the inductor 240. As described above with respect to Fig. 6, the measured current begins to decrease with an increase in the temperature of the current collector 160 until a critical point corresponding to the minimum measured current is reached. At this stage, the controller 330 is configured to wait for a predetermined period of time to allow the current collector 160 to cool before continuing heating. Consequently, the controller 330 controls the DC-to-AC converter 340 to interrupt the supply of power to the inductor 240. After the predetermined period of time has elapsed, the controller 330 controls the DC-to-AC converter 340 to provide power until the critical point corresponding to the minimum measured current is reached again. At this point, controller 340 controls DC/AC converter 340 to again interrupt power supply to inductor 240. Controller 330 again waits for the same predetermined period of time to allow current collector 160 to cool before continuing heating. This heating and cooling of current collector 160 is repeated for the predetermined duration of the preheating process. The predetermined duration of the preheating process is preferably 11 seconds. The predetermined total duration of the preheating process, followed by the calibration process, is preferably 20 seconds.

If the aerosol-forming substrate 110 is dry, the first minimum current of the preheating process is reached within a predetermined period of time, and the power interruption will be repeated until the end of the predetermined period. If the aerosol-forming substrate 110 is wet, the first minimum current of the preheating process will be reached by the end of the predetermined period of time. Therefore, performing the preheating process for a predetermined duration ensures that, regardless of the physical state of the substrate 110, this time is sufficient for the substrate 110 to reach the minimum operating temperature, be ready for continuous power supply, and reach the first maximum value. This allows for calibration to be performed as early as possible, yet without the risk of the substrate 110 not reaching the valley point early.

Furthermore, the aerosol-generating article 100 can be designed such that the minimum current is always achieved within a predetermined duration of the preheating process. If the minimum current is not achieved within a predetermined duration of the preheating process, this may indicate that the aerosol-generating article 100, containing the aerosol-forming substrate 110, is not suitable for use with the aerosol-generating device 200. For example, the aerosol-generating article 100 may contain an aerosol-forming substrate 110 that is different from or of lower quality than the aerosol-forming substrate 100 intended for use with the aerosol-generating device 200. As another example, the aerosol-generating article 100 may not be configured for use with the heating device 320, for example, if the aerosol-generating article 100 and the aerosol-generating device 200 are manufactured by different manufacturers. Thus, the controller 330 may be configured to generate a control signal to terminate the operation of the aerosol-generating device 200.

As mentioned above, as the first step of the calibration process, the pre-heating process can be performed in response to receiving user input, such as user activation of the aerosol-generating device 200. Additionally or alternatively, the controller 330 can be configured to detect the presence of the aerosol-generating article 100 in the aerosol-generating device 200, and the pre-heating process can be performed in response to detecting the presence of the aerosol-generating article 100 within the cavity 220 of the aerosol-generating device 200.

During the operation of the aerosol generating device 200 by the user for generating an aerosol (called the second heating phase), the apparent conductivity (apparent resistance) values at the peak and trough shown in Fig. 6 shift over time. The reason for this, as shown in Fig. 5, is that the apparent resistance of the current collector is the sum of the ohmic resistance R _{of the coil of} the inductor L2 and the ohmic resistance R _{of the load} of the current collector 160. Therefore, any change in the temperature of the inductor L2 during the operation of the device 200 will affect the apparent resistance. Consequently, the calibration values measured during the calibration process in the first heating phase will shift during the operation of the aerosol generating device 200.

During normal operation, when the aerosol-generating device 200 generates an aerosol, the controller 330 will operate in a heating mode to heat the aerosol-forming substrate. The controller 330 can be programmed to enter a recalibration mode from the heating mode to perform additional iterations of at least a portion of the calibration process at predetermined intervals during user operation of the aerosol-generating device 200 to generate an aerosol. The predetermined intervals can be predetermined time intervals or a predetermined number of puffs. Additionally or alternatively, the controller 330 can be programmed to enter a recalibration mode to repeat at least a portion of the calibration process in response to detecting the completion of a puff. The calibration process can take from 200 milliseconds to 2 seconds to complete.

Performing additional iterations of at least part of the calibration process may include re-measuring both calibration values at both critical points (depicted as a peak and a trough in Fig. 6) or re-measuring only the calibration value at one of the critical points, such as at a local maximum of current or conductance (local minimum of resistance).

To perform an additional iteration of the calibration process (in other words, to perform a recalibration), the controller 330 monitors the power supply parameter associated with the current collector 160 by measuring the current I _DC consumed by the power supply and, optionally, the voltage V _DC of the power supply. Since the minimum operating temperature of the aerosol-generating device is greater than the first calibration temperature, as the current collector 160 heats up during additional iterations of the calibration process, the measured current I _DC increases until a critical point is reached and the current I _DC begins to decrease. This critical point corresponds to the end point of the reversible phase transition of the current collector 160, considered as a local maximum conductivity value or current value (local minimum resistance value). The controller 330 records the value of the power supply parameter at the critical point as a re-measured second calibration value.

After reaching the first critical point, the controller 330 controls the DC-to-AC converter 340 to reduce the power supply to the inductor 240 to allow the current collector 160 to cool. For example, the controller 330 may reduce the duty cycle of the DC-to-AC converter 340 to 10%. The controller 330 may reduce the power supply to the inductor 240 until the current collector 160 reaches the appropriate target operating temperature, at which point the controller 300 resumes normal operation in the heating mode.

Alternatively, controller 330 may continue to reduce the power supply to inductor 240 until another critical point is detected. This other critical point corresponds to the end point of the current collector's reversible phase transition, considered as a local minimum conductivity value or current value (local maximum resistance value). Controller 330 records the value of the power supply parameter at the other critical point as a re-measured first calibration value. As described above with respect to the calibration process, the process of measuring the first calibration value and the second calibration value may be repeated at least once during each additional iteration of the calibration process.

Fig. 7 is a graph of conductivity versus time showing the heating profile of susceptor 160. The graph illustrates two successive heating phases: a first heating phase 710, including the preheating process 710A and the calibration process 710B described above, and a second heating phase 720, corresponding to user control of aerosol generating device 200 for generating an aerosol. As described above, during the first heating phase 710, controller 330 operates in calibration mode. After calibration is completed, the controller enters the heating mode and can periodically switch to recalibration mode during the second heating phase 720. It should be understood that Fig. 7 is not shown to scale. In particular, the first heating phase 710 has a shorter duration than the second heating phase 720. For example, the first heating phase 710 can have a duration of 5 seconds to 30 seconds, preferably 10 to 20 seconds. The second heating phase 720 may have a duration of 140 to 340 seconds.

Furthermore, although Fig. 7 shows a graph of conductivity versus time, it should be understood that the controller 330 can be configured to control the heating of the current collector 160 during the first heating phase 710 and the second heating phase 720 based on the measured resistance or current, as described above. Indeed, although the methods for controlling the heating of the current collector during the first heating phase 710 and the second heating phase 720 were described above based on a determined conductivity value or a determined resistance value associated with the current collector, it should be understood that the methods described above can be performed based on the current value measured at the input of the DC/AC converter 340.

As can be seen from Fig. 7, the second heating phase 720 includes a plurality of conductivity stages corresponding to a plurality of temperature stages from the first operating temperature of the susceptor 160 to the second operating temperature of the susceptor 160. The first operating temperature of the susceptor is the temperature at which the aerosol-forming substrate 110 forms an aerosol, so that an aerosol is formed during each temperature stage. Preferably, the first operating temperature of the susceptor is the minimum temperature at which the aerosol-forming substrate will form an aerosol in a sufficient volume and quantity for a satisfactory sensation when inhaled by the user. The second operating temperature of the susceptor is the temperature at the maximum temperature at which it is desirable to heat the aerosol-forming substrate so that the user inhales the aerosol.

The first operating temperature of the current collector 160 is greater than or equal to the first calibration temperature of the current collector 160 corresponding to the first calibration value (a valley in the current graph shown in Fig. 6). The first operating temperature may be from 150 degrees Celsius to 330 degrees Celsius. The second operating temperature of the current collector 160 is less than or equal to the second calibration temperature of the current collector 160 corresponding to the second calibration value at the Curie temperature of the second current collector material (a peak in the current graph shown in Fig. 6). The second operating temperature may be from 200 degrees Celsius to 400 degrees Celsius. The difference between the first operating temperature and the second operating temperature is at least 50 degrees Celsius.

It should be understood that the number of temperature stages illustrated in Fig. 7 is exemplary, and that the second heating phase 720 includes at least three successive temperature stages, preferably from two to fourteen temperature stages, most preferably from three to eight temperature stages. Each temperature stage may have a predetermined duration. Preferably, the duration of the first temperature stage is longer than the duration of subsequent temperature stages. The duration of each temperature stage is preferably more than 10 seconds, preferably from 30 to 200 seconds, more preferably from 40 to 160 seconds. The duration of each temperature stage may correspond to a predetermined number of user puffs. Preferably, the first temperature stage corresponds to four user puffs, and each subsequent temperature stage corresponds to one user puff.

During the duration of each temperature step, the temperature of the current collector 160 is maintained within the target operating temperature corresponding to the respective temperature step. Thus, during the duration of each temperature step, the controller 330 regulates the power supply to the heating device 320 such that the measured parameter of the power source is maintained within the target value corresponding to the target operating temperature of the respective temperature step, wherein the target value is determined with reference to the first calibration value and the second calibration value, as described above.

As an example, the second heating phase 720 may comprise five temperature steps: a first temperature step 720a having a duration of 160 seconds and a target conductivity value G _Target =G _Lower +(0.09×ΔG), a second temperature step 720b having a duration of 40 seconds and a target conductivity value G _Target =G _Lower +(0.25×ΔG), a third temperature step 720c having a duration of 40 seconds and a target conductivity value G _Target =G _Lower +(0.4×ΔG), a fourth temperature step 720d having a duration of 40 seconds and a target conductivity value G _Target =G _Lower +(0.56×ΔG) and a fifth temperature step 720e having a duration of 85 seconds and a target conductivity value G _Target =G _Lower +(0.75×ΔG). These temperature steps can correspond to temperatures of 330 degrees Celsius, 340 degrees Celsius, 345 degrees Celsius, 355 degrees Celsius and 380 degrees Celsius.

Thus, the control of the operating temperature of the aerosol-generating susceptor 160 depends on the first calibration value (corresponding to the first calibration temperature) and the second calibration value (corresponding to the second calibration temperature), measured during the calibration process. However, the shift in the apparent conductivity of the susceptor during the second heating phase 720 means that for the same temperature of the susceptor, the apparent conductivity value decreases during the second heating phase 720. Therefore, in order to ensure the possibility of precise control of the temperature of the susceptor, as well as to prevent overheating of the aerosol-generating substrate 110, the controller 330 is programmed to periodically enter the recalibration mode to repeat at least a part of the calibration process during the second heating phase 720. For example, at least a part of the calibration process is repeated at an interval of 15 seconds to 2 minutes. Preferably, at least a part of the calibration process is repeated every 30 seconds. This is shown in Fig. 8, which shows the second heating phase 720 in more detail, including recalibration during each temperature step. As before, Fig. 8 is for illustrative purposes and is not drawn to scale.

As described above, at least the second calibration value is re-measured during additional iterations of the calibration process, as shown in Fig. 8. Optionally, the first calibration value is re-measured during additional iterations of the calibration process. The target values of the power source parameter corresponding to each temperature step can be stored in the memory of the controller 330 and updated after each iteration of the calibration process. The controller 330 can adjust the target value of the power source parameter for each corresponding temperature step based on at least one of the re-measured calibration values, in other words, based on at least the re-measured second calibration value. Additionally or alternatively, the controller 330 can adjust the target values of the power source parameter for each corresponding temperature step based on the re-measured first calibration value. Additionally or alternatively, the controller 330 may adjust the target value of the power source parameter for each respective temperature stage based on a combination of one or more calibration values measured during the first heating phase 710 and one or more calibration values measured during at least one additional iteration of the calibration process during the second heating phase 720.

Therefore, in the above example for the first temperature stage 720a, the target conductivity will be based, at least initially upon starting the heating mode, on the calibration values _GLower and ΔG obtained during the calibration process 710B of the first heating phase 710. Based on the fact that the controller 330 is programmed to repeat the calibration process every 30 seconds, the calibration process will be repeated five times during the first temperature stage, after 30 seconds, 60 seconds, 90 seconds, 120 seconds, and 150 seconds. The calibration process will be repeated once during the second temperature stage 720b after 180 seconds (20 seconds after the start of the second temperature stage). The calibration process will be repeated once during the third temperature step 720c after 210 seconds (10 seconds after the start of the third temperature step) and at the end of the third temperature step 720c after 240 seconds. The calibration process will be repeated once during the fourth temperature step 720o! after 280 seconds (30 seconds after the start of the third temperature step). The calibration process will be repeated twice during the fifth temperature step 720e after 320 seconds (20 seconds after the start of the fifth temperature step) and after 350 seconds (50 seconds after the start of the fifth temperature step). After each additional iteration of the calibration process, the controller 330 will adjust G _Target based, at least in part, on at least one of the calibration values obtained as a result of the last additional iteration of the calibration process. For example, the target conductivity after each recalibration is adjusted based, at least in part, on the re-measured calibration values G _{Lower_i} and ΔG _i obtained during the corresponding recalibration process, or on the calibration value G _Lower and the re-measured value ΔG _i obtained during the corresponding recalibration process, where i = the start time of the second heating phase 720 + 30 seconds.

During the second heating phase 720, the user will draw the aerosol generated by the aerosol-generating device into their body. In other words, the user will puff through the mouthpiece 140 of the aerosol-generating article, which is partially housed in the aerosol-generating device 200. When the user puffs, cold air is drawn into the aerosol-generating device 200 through the aerosol-generating article 100, thereby cooling the susceptor 160. Therefore, if recalibration is performed during a puff, the temporary cooling of the susceptor 160 temporarily reduces the difference between the calibration values (e.g., a decrease in the ΔG value). In other words, again referring to FIG. 6, there is a temporary decrease in the current value at the peak and a temporary increase in the current value at the trough during the puff. Therefore, the calibration values measured during the user's puff will not be accurate. Specifically, if calibration values obtained during a puff were used to control the temperature of current collector 160, there would be a risk of current collector 160 overheating, resulting in the release of unwanted aerosol components. Therefore, controller 330 is programmed so that recalibration does not coincide with a puff.

The induction heating device may be a portable induction heating device. The induction heating device may be limited in the number or size of the electronic components contained within the induction heating device. Additionally or alternatively, the components contained within the induction heating device may be limited in terms of processing power or memory.

An induction heating device or a controller associated with the induction heating device may be configured to obtain conductivity values and process these conductivity values to calibrate the induction heating device. The relationship between the conductivity values and the temperature of the current collector may be known for at least one point. For example, the temperature for at least one of the equalized characteristic and the peak point of the conductivity calibration curve may be known. Thus, a calibrated induction heating device can avoid exceeding the Curie temperature of the current collector. The Curie temperature may be the temperature above which the current collector loses its permanent magnetic properties.

Calibration may include determining a minimum point of the calibration curve, which may be referred to as the S curve, and at least one of a peak point and a plateau of the calibration curve. The calibration curve may have a minimum, an inflection point, and at least one of a maximum and a plateau.

The first characteristic point of the calibration curve may be a minimum on the calibration curve, followed by an inflection point and at least one of a maximum and a plateau characteristic of the calibration curve. The maximum may correspond to the peak point at which the power supplied to the induction heating device is gradually reduced to prevent overheating. Detection of the minimum, which may also be referred to as a valley or valley point in this application, can be accomplished by various methods known in the art. However, determining the maximum or plateau characteristic of the calibration curve may be difficult.

The first and second calibration values, as described above, can be determined based on the determined at least one of the aligned characteristic and the peak point value.

Accordingly, it would be desirable to provide an improved method for reliably determining the maximum or flattened characteristic of a calibration curve quickly and efficiently. Due to the limited computing power of an induction heating device, it would be desirable to keep the mathematical operations as simple as possible. Additionally, it would be desirable to detect overheating or determine the maximum or flattened characteristic of a calibration curve in less than 200 ms.

Calibration can be represented by one of two types of curves: a calibration curve and a recalibration curve. A calibration curve may begin with a clearly defined valley and then gradually increase over a period of one to several seconds before reaching the plateau of the calibration curve. A recalibration curve may not contain a valley before increasing, may be shorter, and its duration may be as short as 300 ms before reaching the plateau of the calibration curve.

Fig. 8 shows a flow chart of a method 800 for determining a flattened characteristic or peak point for calibrating an induction heating device for an aerosol-generating system. The method includes, at step 810, obtaining a sequence of calibration values of the induction heating device for the aerosol-generating system. The sequence of calibration values is associated with a calibration curve. Controller 330, as described above, can be programmed to perform method 800.

At step 820, the sequence of calibration values is smoothed to obtain a sequence of smoothed calibration values. The calibration curve C may be smoothed by convolving it with (half) a Gaussian kernel G with standard deviation σ to remove noise.

At step 830, the first derivative of the sequence of smoothed calibration values is determined. The first derivative can be determined using the convolution property, which has the following form:

where g is a (symmetric) Gaussian kernel with standard deviation 2⋅σ. σ can denote the standard deviation of a centered Gaussian density function. * can denote the convolution product of two functions or discrete sequences. The resulting first derivative is denoted as Z(t). Using the associativity of convolution, the first derivative can be defined as follows:

The first derivative of the smoothed calibration sequence can be determined every millisecond. The first derivative of the smoothed calibration value sequence can be determined as follows:

At step 840, the maximum value of the first derivative of the sequence of smoothed calibration values is estimated. The shape of the calibration curve, including the inflection point and the smoothed property, ensures that Z has a maximum value that can be reliably detected. The maximum of Z(t) may occur at time tmax and be estimated by determining the time point at which Z(tmax) is lower than the average value nmax of the previous steps. nmax may denote the number of time steps used to reliably detect the maximum.

At step 850, at least one of the aligned characteristic and the peak point value is determined based on a first threshold associated with the estimated maximum value of the first derivative. For example, the search for at least one of the aligned characteristic and the peak point value can begin as soon as Z(t) decreases again after a maximum below p ₁ ⋅ Z(tmax) (at time tp1). p1 can determine a fraction of Z(tmax) below which Z(t) must be to begin the search for at least one of the aligned characteristic and the peak point value. For example, pi can be 0.1 for the calibration curve and 0.2 for the recalibration curve. At least one of the aligned characteristic and the peak point value can be determined as follows:

Maximum Z(t) detection and start time for alignment detection:

Heating of the induction heating device may be terminated in response to determining at least one of the leveled characteristic and the peak point value, so that the induction heating device does not heat above a temperature associated with at least one of the leveled characteristic and the peak point value. The first termination criterion may be obtained at time tstop, where Z(t _stop <=Pstop ₁ ⋅ Z(t _max ). pstop1 may determine the fraction of Z(tmax) below which Z(t) must be for the first termination criterion to be met.

At step 860, the heating of the induction heating device may be terminated when the first derivative of the sequence of smoothed calibration values increases again after the maximum value of the first derivative of the sequence of smoothed calibration values. For example, the second termination criterion may be obtained if a repeatedly increasing pattern of Z(t) is detected after t _p1 /2 by checking whether 80% of nstop2 consecutive steps increase again using reliable criteria _where MA _n (x) is the moving average (twist) of order n of x. ME _n (x) may represent the moving median of order n of x. nstop2 may determine the size of the smoothing kernel to apply for the second stopping criterion.

The detection of the termination of heating by the induction heating device can be performed as follows:

Termination Criteria:

Result: stop ₁ , stop ₂ termination criterion

Input: t _m >t _α t _p1 , Z(t _m ), p _stop1 , n _stop2

Conclusion: Stop criterion stop ₁ , stop ₂

1. if t _p1 >0, then

2. m←p1

3. if stop ₁ =FALSE and stop ₂ =FALSE execute

4. if Z(t _m )<Z _max or Z(t _m )<p _stop1 ⋅Z(t _max ), then

5. stop ₁ ←true

6. end

7. c←NULL

8. Calculate the previous average values from m _p1

9. if m>m _p1 +n _stop2 +1, then

10.

11. if That

12. c=concat(c,1)

13. end

14. Otherwise

15. c=concat(c,0)

16. end

17. if len(c)≥n _stop2 , then

18.

19. if p>0.8, then

20. stop ₂ ←TRUE

21. end

22. end

23. end

24. m = m + n Steps

25. end

26. end

Steps 810-860 can be repeated periodically. For example, steps 810-860 could be repeated every 10 ms.

In step 870, the induction heating device is operated in accordance with at least one of the determined equalized characteristic and the peak point value. Operating the induction heating device in accordance with at least one of the determined equalized characteristic and the peak point value may include maintaining the temperature associated with the aerosol generating system below a specific temperature based on at least one of the determined equalized characteristic and the peak point value. Calibration curves may have different shapes and/or slopes. For example, the slope of the calibration curve may depend on the humidity of the substrate to be heated. Thus, different time intervals may be required for calibrating different calibration curves, which may affect the level of smoothing required to detect the characteristic points of the calibration curve. Recalibration may be shorter than calibration. The recalibration curve may have a steeper slope compared to the calibration curve. For example, recalibration can be performed at 300 ms until at least one of the aligned characteristic and the peak point value is determined. Prediction of the duration of such curves can be performed using machine learning using time derivatives as input. The derivatives (or their approximate values) can serve as training features and can be calculated directly from the conductance for the first 38 ms using MA ₁₀ for curve smoothing. The features can be calculated as:

for t _i >t _valley +10 ^-2 +2.

Method 800 can automatically scale at least one parameter used to determine at least one of the aligned characteristic and the peak point value. For example, in step 802, the calibration curve type can be determined by classifying the calibration curve. The calibration curve can be classified based on the slope of the calibration curve. The type can be associated with one of the recalibration curve and the calibration curve, and the slope of one of the recalibration curve and the calibration curve. The calibration curve type can be determined based on a second threshold associated with the estimated maximum value of the first derivative of the sequence of smoothed calibration values.

In step 804, based on the determined type of calibration curve, at least one parameter can be selected for calibration. The at least one parameter can include at least one of a first parameter that indicates a first threshold for the step of determining at least one of the leveled characteristic and the peak point value, a second parameter that indicates smoothing of the sequence of calibration values, a third parameter that indicates the number of successive values of the first derivative of the sequence of smoothed calibration values used for the step of estimating the maximum value of the first derivative, a fourth parameter that indicates the number of successive values of the first derivative of the sequence of smoothed calibration values used for the step of determining at least one of the leveled characteristic and the peak point value, and a fifth parameter that indicates the number of values of the first derivative of the sequence of smoothed calibration values used for the step of determining a repeated increase of the first derivative of the sequence of smoothed calibration values after the maximum value of the first derivative of the sequence of smoothed calibration values. The second threshold can determine a proportion of the maximum value of the first derivative of the sequence of smoothed calibration values.

Recalibration curves can be classified as "short-R" or "long-R" based on a threshold associated with the approximate time t= _tmax of the first derivative's maximum. Figure 9A shows a classification tree that can be trained on the recalibration curves tested. The classification tree is a depth-one tree.

Calibration curves can be classified as "short-C,""medium-C," or "long-C" based on a threshold associated with the approximate time t= _tmax of the first derivative's maximum. Figure 9B shows a classification tree that can be trained on test calibration curves. The classification tree can be a depth-2 tree. Alternatively, the recalibration curve and the calibration curve can be classified based on a threshold indicating the slope of the calibration curve. For example, the mean value of the calibration curve at a specified time after the valley point can be compared to the threshold.

Based on the prediction category, knowing whether the curve is a calibration curve or not, the predicted category can be used to select a predefined set of parameters. To reduce computation time, Z(t _m ) can be calculated every 2 ms (m = 1, 3, 5, 7, …, 2n-1, …) and can be defined for even stages. Parameters for calibration can be defined as follows:

Result:

C(t), calibration or recalibration: t _m

Set of parameters: σ, p ₁ , n _max , n _stop2 , p _stop1

1. Calculate

2. Receive

3. cRecalib=0.04339134

4. cCalib1=0.6036762

5. cCalib2=0.05115039

6. P _stop1 = 0.02

7. if curveType="Recalib", then

8. p1=0.02

9. if δ ₁ ≥cRecalib, then

10. out="short - R"

11. end

12. Otherwise

13. out="medium - R"

14. end

15. end

16. otherwise

17. p ₁ = 0.1

18. if δ ₂₇ <cCalib1, then

19. if δ ₁₃ <cCalib2, then

20. out="long - C"

21. end

22. Otherwise

23. out="medium - C"

24. end

25. end

26. Otherwise

27. out="short - C"

28. end

29. end

30. if out="short - R", then

31. σ=0.01

32. n _max = 11

33. n _stop2 = 5

34. end

35. Otherwise, if out="medium - R", then

36. σ=0.03

37. n _max = 25

38. n _stop2 = 15

39. end

40. Otherwise, if out="short - C", then

41. σ=0.05

42. n _max = 25

43. n _stop2 = 15

44. end

45. Otherwise, if out="medium - C", then

46. σ=0.1

47. n _max = 50

48. n _stop2 = 50

49. p _stop1 = 0.01

50. end

51. Otherwise

52. σ=0.2

53. n _max = 75

54. n _stop2 = 100

55. pstop ₁ = 0.01

56. end

In the experiments, the relative and absolute difference between the conductivity at the moment of stopping and the expected maximum conductivity were calculated. The relative difference between the detected maximum and the maximum conductivity and δ _S (loss) were calculated as for a calibration curve where c=valley is present, or where there is no depression.

An example of a recalibration curve 1010 is shown in Fig. 10. Fig. 10 also shows the determined peak point value 1020 and the point 1030 that meets the termination criteria.

For the purposes of the present description and the appended claims, except where otherwise indicated, all numbers expressing quantities, amounts, percentages, etc., shall be understood as modified in all instances by the term "about." Also, all ranges include the disclosed maximum and minimum points and include any intermediate ranges therebetween, which may or may not be specifically listed herein. In this context, the number A may be considered to include numerical values that are within the common standard error for measuring the property that the number "A" modifies. The number A, in some instances, when used in the appended claims, may deviate by the percentages listed above, provided that the amount by which A deviates does not materially affect the fundamental and novel characteristic(s) of the claimed invention. Also, all ranges include the disclosed maximum and minimum points and include any intermediate ranges therebetween, which may or may not be specifically listed herein.

Claims (32)

1. A method for calibrating an induction heating device for an aerosol generating system, performed by a controller and comprising: obtaining a sequence of calibration values of an induction heating device for an aerosol generating system, wherein the sequence of calibration values is associated with a calibration curve, wherein the induction heating device comprises an inductor that is configured to be connected to a current collector for heating an aerosol forming substrate, wherein the sequence of calibration values comprises one of a sequence of conductivity values and a sequence of resistance values, and wherein a value in the sequence of calibration values is associated with a calibration temperature of the current collector; smoothing a sequence of calibration values to obtain a sequence of smoothed calibration values; determination of the first derivative of a sequence of smoothed calibration values; estimating the maximum value of the first derivative of the sequence of smoothed calibration values; and determining at least one of the aligned characteristic and the peak point value based on a first threshold associated with the estimated maximum value of the first derivative. 2. The method according to paragraph 1, characterized in that smoothing of the sequence of calibration values and determination of the first derivative of the sequence of smoothed calibration values are performed in one calculation. 3. The method according to paragraph 1 or 2, characterized in that the evaluation of the maximum value of the first derivative of the sequence of smoothed calibration values includes a comparison of the value of the first derivative of the sequence of smoothed calibration values with a given number of values of the first derivative of the sequence of smoothed calibration values. 4. The method according to paragraph 1 or 2, characterized in that the value of the first derivative of the sequence of smoothed calibration values is estimated as the maximum value if the average value of a given number of previous values of the first derivative of the sequence of smoothed calibration values is higher than the value of the first derivative of the sequence of smoothed calibration values. 5. The method according to any one of paragraphs 1-4, characterized in that the first threshold is a fraction of the maximum value of the first derivative of the sequence of smoothed calibration values. 6. The method according to any one of paragraphs 1-5, characterized in that it further includes stopping heating of the induction heating device when the first derivative of the sequence of smoothed calibration values increases again after the maximum value of the first derivative of the sequence of smoothed calibration values. 7. The method according to claim 6, characterized in that the repeated increase in the first derivative of the sequence of smoothed calibration values after the maximum value of the first derivative of the sequence of smoothed calibration values is determined if the average value of a specific number of consecutive values of the first derivative increases over time. 8. The method according to any one of paragraphs 1-7, characterized in that it further includes determining the type of the calibration curve by classifying the calibration curve; and selecting, based on a determined type of calibration curve, at least one parameter for calibration. 9. The method according to claim 8, characterized in that the calibration curve is classified based on the slope of the calibration curve. 10. The method according to any one of paragraphs 1-9, characterized in that it further includes stopping heating of the induction heating device in response to determining at least one of the leveled characteristic and the peak point value. 11. An induction heating device for an aerosol generating system comprising a controller configured to: obtaining a sequence of calibration values of an induction heating device, wherein the sequence of calibration values is associated with a calibration curve; smoothing a sequence of calibration values to obtain a sequence of smoothed calibration values; determining the first derivative of a sequence of smoothed calibration values; estimates of the maximum value of the first derivative of a sequence of smoothed calibration values; and determining at least one of the aligned characteristic and the peak point value based on a first threshold associated with the estimated maximum value of the first derivative, wherein the induction heating device is configured to operate in accordance with at least one of the equalized characteristic and the peak point value, wherein the induction heating device comprises an inductor which is configured to be connected to a current collector for heating an aerosol-forming substrate, wherein the sequence of calibration values comprises one of a sequence of conductivity values and a sequence of resistance values, and wherein the value in the sequence of calibration values is associated with a calibration temperature of the current collector. 12. An induction heating device according to paragraph 11, characterized in that it contains: power supply for supplying DC and DC power supply voltage; an electronic circuit of a power supply unit connected to a power source, wherein the electronic circuit of a power supply unit comprises: DC to AC converter; an inductor, wherein the inductor is connected to a DC to AC converter to generate an alternating magnetic field when excited by an alternating current from the DC to AC converter; and a controller, wherein the controller is configured to control the power supplied to the electronic circuit of the power supply unit, ensuring an increase in the temperature of the current collector. 13. The induction heating device according to claim 12, characterized in that it further comprises a current sensor configured to measure, on the input side of the DC to AC converter, the DC current consumed from the power source; and a voltage sensor configured to measure, on the input side of the DC to AC converter, the DC supply voltage of the power source, wherein the sequence of calibration values comprises a sequence of conductivity values or a sequence of resistance values, and wherein the conductivity values or the resistance values associated with the current collector are determined from the DC supply voltage of the power source and the DC current consumed from the power source. 14. An aerosol generating system comprising an induction heating device according to any one of paragraphs 11-13 and an aerosol generating article, wherein the aerosol generating article comprises an aerosol forming substrate and a current collector.