Method for calibrating an induction heating device

Abstract

A method of calibrating an inductive heating device for an aerosol generating system is disclosed that includes obtaining a sequence of calibration values ​​for an inductive heating device for an aerosol generating system, the sequence of calibration values ​​being associated with a calibration curve, smoothing the sequence of calibration values ​​to obtain a sequence of smoothed calibration values, determining a first derivative value of the smoothed sequence of calibration values, estimating a maximum value of the first derivative value of the smoothed sequence of calibration values, determining at least one of a plateau characteristic and a hill point value based on a first threshold value associated with the maximum value of the estimated first derivative value, and operating the inductive heating device in accordance with the determined at least one of the plateau characteristic and the hill point value.

Description

[Technical field]

[0001] The present disclosure relates to an induction heating device for heating an aerosol-forming substrate. The present disclosure further relates to a method for calibrating an induction heating device. [Background technology]

[0002] The aerosol generating device may include an electrically operated heat source configured to heat the aerosol-forming substrate to generate the aerosol. It is therefore important for the aerosol generating device to accurately monitor and control the temperature of the electrically operated heat source to ensure optimal generation and delivery of the aerosol to the user. It is particularly important to ensure that the electrically operated heat source does not overheat the aerosol-forming substrate, as overheating may lead to combustion of the aerosol-forming substrate, which would result in the generation of undesirable compounds as well as unpleasant tastes and aromas for the user.

[0003] It is desirable to provide an efficient and rapid method for calibrating an induction heating device that reduces the risk of overheating and provides reliable temperature regulation to ensure continued normal operation of the aerosol generating device. Summary of the Invention

[0004] 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 ​​for an induction heating device for an 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 a first derivative of the smoothed sequence of calibration values, estimating a maximum value of the first derivative of the smoothed sequence of calibration values, determining at least one of a plateau characteristic and a hill point value based on a first threshold associated with the maximum value of the estimated first derivative value, and operating the induction heating device according to the determined at least one of the plateau characteristic and the hill point value. The induction heating device may be a handheld induction heating device. Alternatively, the induction heating device may be part of the handheld device.

[0005] By estimating a maximum value of the first derivative of the sequence of smoothed calibration values, determining at least one of a plateau characteristic and a hill point value based on a first threshold value associated with the maximum value of the estimated first derivative value, and operating the induction heating device according to the determined at least one of the plateau characteristic and the hill point value, a feature point or characteristic feature of the calibration curve can be determined quickly, robustly and reliably. By operating the induction heating device according to the determined at least one of the plateau characteristic and the hill point value, the feature point or characteristic feature of the calibration curve can be used to prevent overheating of the device for improved safety of the user. For example, formation of undesirable components can be avoided when the aerosol-forming substrate is heated above a critical temperature.

[0006] The steps of smoothing the sequence of calibration values ​​and determining the first derivative of the smoothed sequence of calibration values ​​may be performed in one calculation, which may save computational resources.

[0007] The step of estimating a maximum value of the first derivative value of the sequence of smoothed calibration values ​​may include comparing the value of the first derivative value of the sequence of smoothed calibration values ​​to a predetermined number of values ​​of the first derivative value of the sequence of smoothed calibration values. Alternatively, the value of the first derivative value of the sequence of smoothed calibration values ​​may be estimated as a maximum value when an average of a predetermined number of previous values ​​of the first derivative value of the sequence of smoothed calibration values ​​is higher than the value of the first derivative value of the sequence of smoothed calibration values.

[0008] The first threshold may be a fraction of a maximum value of the first derivative value of the sequence of smoothed calibration values. By determining at least one of the plateau characteristic and the hill point value based on the first threshold being a fraction of a maximum value of the first derivative value of the sequence of smoothed calibration values, a robust method for determining at least one of the plateau characteristic and the hill point value is provided, since at least the plateau characteristic may be determined even if the calibration curve does not have a maximum.

[0009] The method may include ceasing heating of the induction heating device when the first derivative value of the sequence of smoothed calibration values ​​increases again after a maximum value of the first derivative value of the sequence of smoothed calibration values. A re-increase of the first derivative value of the sequence of smoothed calibration values ​​after a maximum value of the first derivative value of the sequence of smoothed calibration values ​​may be determined when an average of a certain number of consecutive values ​​of the first derivative value increases over time.

[0010] A rescue method is provided to protect against overheating by stopping the induction heating device when the first derivative of the sequence of smoothed calibration values ​​increases again.

[0011] The method may further include determining a type of the calibration curve by classifying the calibration curve and selecting at least one parameter for calibration based on the determined type of calibration curve. The calibration curve may be classified based on a slope of the calibration curve. Alternatively or additionally, the calibration curve may be classified based on a time corresponding to a maximum value of the first derivative value.

[0012] This further improves the accuracy and reliability of the calibration process since the parameters can be selected for a specific calibration curve.

[0013] The method may further include ceasing heating of the induction heating device in response to determining at least one of the plateau characteristic and the hill point value, thereby providing an efficient and safe calibration method since the method does not need to heat beyond the hill point to determine the hill point.

[0014] According to one embodiment of the present invention, an induction heating apparatus for an aerosol generating system is provided, the induction heating apparatus comprising a controller configured to: obtain a sequence of calibration values ​​for the induction heating apparatus, the sequence of calibration values ​​being associated with a calibration curve; smooth the sequence of calibration values ​​to obtain a sequence of smoothed calibration values; determine a first derivative value of the smoothed sequence of calibration values; estimate a maximum value of the first derivative value of the smoothed sequence of calibration values; and determine at least one of a plateau characteristic and a hill point value based on a first threshold value associated with the maximum value of the estimated first derivative value. The induction heating apparatus operates according to the at least one of the determined plateau characteristic and the hill point value. The induction heating apparatus may comprise an inductor inductively coupleable to a susceptor for heating the aerosol-forming substrate, the calibration value being associated with the susceptor. The induction heating apparatus may comprise a power supply for providing a DC supply voltage and a DC current, and power supply electronics connected to the power supply. The power electronics may include a DC / AC converter, an inductor connected to the DC / AC converter for generating an alternating magnetic field when energized with an alternating current from the DC / AC converter, and a controller configured to control power provided to the power electronics to increase a temperature of the susceptor. Obtaining the sequence of calibration values ​​may include measuring a current associated with the supply electronics of the induction heating device.

[0015] This provides an improved induction heating device that can reliably and robustly determine at least one of the plateau characteristics and hill point values ​​in order to calibrate the induction heating device for temperature without continuously measuring temperature.

[0016] According to one embodiment of the present invention, there is provided an aerosol-generating system comprising an induction heating apparatus as described above and an aerosol-generating article, the aerosol-generating article comprising an aerosol-forming substrate and a susceptor.

[0017] The term "aerosol-generating device" as used herein 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 that includes an aerosol-forming substrate and a cartridge that includes an 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 operated aerosol-generating device may include an atomizer, such as an electric heater, for heating the aerosol-forming substrate to form an aerosol.

[0018] The term "aerosol-generating system" as used herein refers to the combination of an aerosol-generating device with an aerosol-forming substrate. When the aerosol-forming substrate forms part of an aerosol-generating article, the aerosol-generating system refers to the combination of an aerosol-generating device with an aerosol-generating article. In an aerosol-generating system, the aerosol-forming substrate and the aerosol-generating device work together to generate an aerosol.

[0019] The term "aerosol-forming substrate" as used herein refers to a substrate capable of releasing a volatile compound capable of forming an aerosol. The volatile compound may be released by heating or burning the aerosol-forming substrate. As an alternative to heating or burning, in some cases the volatile compound may be released by a chemical reaction or by mechanical stimulation such as ultrasound. The aerosol-forming substrate may be solid or may include both solid and liquid components. The aerosol-forming substrate may be part of an aerosol-generating article.

[0020] The term "aerosol-generating article" as used herein refers to an article that includes an aerosol-forming substrate capable of emitting a volatile compound capable of forming an aerosol. The aerosol-generating article may be disposable. An aerosol-generating article that includes an aerosol-forming substrate that includes tobacco may be referred to herein as a tobacco stick.

[0021] The aerosol-forming substrate may comprise nicotine. The aerosol-forming substrate may comprise tobacco, for example a tobacco-containing material containing volatile tobacco flavour compounds that are released from the aerosol-forming substrate upon heating. In a preferred embodiment, the aerosol-forming substrate may comprise homogenized tobacco material, for example cast 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 flavour 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 former. Examples of suitable aerosol formers are glycerin and propylene glycol.

[0022] As used herein, the term "susceptor" refers to an element that includes a material capable of converting the energy of a magnetic field into heat. When the susceptor is located in an alternating magnetic field, the susceptor heats up. The heating of the susceptor can be the result of at least one of hysteresis losses and eddy currents induced in the susceptor, depending on the electrical and magnetic properties of the susceptor material.

[0023] As used herein in referring to an aerosol generating device, the terms "upstream" and "forward," as well as "downstream" and "rearward," are used to describe the relative locations of components, or portions of components, of the aerosol generating device in relation to the direction in which air flows through the aerosol generating device during use. An aerosol generating device according to the invention comprises a proximal end through which aerosol exits the device during use. The proximal end of the aerosol generating device may also be referred to as the mouth end or downstream end. The mouth end is 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 device may be described as being upstream or downstream of one another based on their relative location with respect to the airflow path of the aerosol generating device.

[0024] As used herein when referring to an aerosol-generating article, the terms "upstream" and "forward", as well as "downstream" and "backward" are used to describe the relative positions of components or parts of components of the aerosol-generating article in relation to the direction in which air flows through the aerosol-generating article during use of the aerosol-generating article. The aerosol-generating article according to the present invention comprises 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 mouth end or the downstream end. The mouth end is downstream of the distal end. The distal end of the aerosol-generating article may also be referred to as the upstream end. Components or parts of components of the aerosol-generating article may be described as being upstream or downstream of each other 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 of a component or part of a component of the aerosol-generating article is the part that is at the end closest to the upstream end of the aerosol-generating article. The back of a component or part of a component of the aerosol-generating article is the part that is at the end closest to the downstream end of the aerosol-generating article.

[0025] As used herein, the term "inductively coupled" refers to heating a susceptor when penetrated by an alternating magnetic field. The heating may be caused by the generation of eddy currents in the susceptor. The heating may also be caused by magnetic hysteresis losses.

[0026] The present invention is defined in the claims. However, below is provided a non-exhaustive list of non-limiting examples. Any one or more of the features of these examples may be combined with any one or more features of any other example, embodiment, or aspect described herein.

[0027] Example 1: 1. A method for calibrating an induction heating device for an aerosol generating system, the method comprising: obtaining a sequence of calibration values ​​for an induction heating device for an aerosol generating system, the sequence of calibration values ​​being associated with a calibration curve; smoothing the sequence of calibration values ​​to obtain a sequence of smoothed calibration values; determining a first derivative value of the smoothed sequence of calibration values; estimating a maximum value of the first derivative value of the smoothed sequence of calibration values; determining at least one of a plateau characteristic and a hill point value based on a first threshold value associated with the maximum value of the estimated first derivative value; and operating the induction heating device in accordance with the determined at least one of the plateau characteristic and the hill point value. Example 2: 2. The method according to example 1, wherein smoothing comprises convolving the sequence of calibration values ​​with at least one Gaussian kernel. Example 3: 3. The method according to example 2, wherein the at least one Gaussian kernel comprises a half-Gaussian kernel. Example 4: 3. The method according to any one of the preceding claims, wherein the at least one Gaussian kernel comprises a symmetric Gaussian kernel. Example 5: The method according to example 1, wherein smoothing comprises convolving the sequence of calibration values ​​with a half-Gaussian kernel and a symmetric Gaussian kernel, the half-Gaussian kernel and the symmetric Gaussian kernel being associated with different standard deviations. Example 6: A method according to any of Examples 1-5, wherein smoothing the sequence of calibration values ​​and determining the first derivative value of the smoothed sequence of calibration values ​​are performed in one calculation. Example 7: The method according to any of Examples 1 to 6, wherein estimating the maximum value of the first derivative value of the sequence of smoothed calibration values ​​includes comparing the value of the first derivative value of the sequence of smoothed calibration values ​​to a predetermined number of values ​​of the first derivative value of the sequence of smoothed calibration values. Example 8: The method according to any of the first to sixth embodiments, wherein the value of the first derivative value of the sequence of smoothed calibration values ​​is estimated as a maximum value when an average of a predetermined number of previous values ​​of the first derivative value of the sequence of smoothed calibration values ​​is higher than the value of the first derivative value of the sequence of smoothed calibration values. Example 9: A method according to any of Examples 1-8, wherein the first threshold is a fraction of a maximum value of the first derivative value of the sequence of smoothed calibration values. Example 10: The method according to any of Examples 1-9, further comprising: ceasing heating of the induction heating device when the first derivative value of the sequence of smoothed calibration values ​​increases again after a maximum value of the first derivative value of the sequence of smoothed calibration values. Example 11: A method according to example 10, wherein a re-increase in the first derivative value of the sequence of smoothed calibration values ​​after a maximum value of the first derivative value of the sequence of smoothed calibration values ​​is determined when the average of a certain number of consecutive values ​​of the first derivative value increases over time. Example 12: The method according to any of Examples 1 to 11, further comprising determining a type of the calibration curve by classifying the calibration curve, and selecting at least one parameter for calibration based on the determined type of the calibration curve. Example 13: The method according to example 12, wherein the calibration curves are classified based on the slope of the calibration curve. Example 14: The method according to any of Examples 12 and 13, wherein the type is associated with one of the recalibration curve and the calibration curve, and with the slope of one of the recalibration curve and the calibration curve. Example 15: A method according to any of Examples 12-14, wherein the type of the calibration curve is determined based on a second threshold associated with a maximum value of the first derivative value of the sequence of estimated smoothed calibration values. Example 16: The method according to any of Examples 12-15, wherein a first parameter of the at least one parameter specifies a first threshold value for determining at least one of a plateau characteristic and a hill point value. Example 17: The method according to any of Examples 12 to 16, wherein a second parameter of the at least one parameter specifies a smoothing of the sequence of calibration values. Example 18: The method according to any of embodiments 12 to 17, wherein a third parameter of the at least one parameter specifies the number of consecutive values ​​of the first derivative value in the sequence of smoothed calibration values ​​used in the step of estimating the maximum value of the first derivative value. Example 19: The method according to any one of Examples 12 to 18, wherein a fourth parameter of the at least one parameter specifies the number of consecutive values ​​of the first derivative value of the sequence of smoothed calibration values ​​used in the step of determining at least one of the plateau characteristic and the hill point value. Example 20: The method according to any of embodiments 12 to 19, wherein a fifth parameter of the at least one parameter specifies the number of values ​​of the first derivative value of the sequence of smoothed calibration values ​​used in the step of determining a re-increase of the first derivative value of the sequence of smoothed calibration values ​​after a maximum value of the first derivative value of the sequence of smoothed calibration values. Example 21: A method according to any of embodiments 12-20, wherein the second threshold is a fraction of a maximum value of the first derivative value of the sequence of smoothed calibration values. Example 22: A method according to example 1, wherein operating the induction heating device in accordance with at least one of the determined plateau characteristics and hill point values ​​includes maintaining a temperature associated with the aerosol generation system below a particular temperature based on at least one of the determined plateau characteristics and hill point values. Example 23: The method according to any of Examples 1-22, further comprising: in response to determining at least one of the plateau characteristic and the hill point value, ceasing heating of the induction heating device. Example 24: A method according to any of Examples 1-23, wherein the sequence of calibration values ​​is obtained during a calibration phase of the induction heating device. Example 25: A method according to any of Examples 1-23, wherein the sequence of calibration values ​​is obtained during a recalibration of the induction heating device. Example 26: 1. An inductive heating device for an aerosol generation system, comprising: a controller configured to: obtain a sequence of calibration values ​​for the inductive heating device, the sequence of calibration values ​​being calibration values ​​associated with a calibration curve; smooth the sequence of calibration values ​​to obtain a sequence of smoothed calibration values; determine a first derivative value of the smoothed sequence of calibration values; estimate a maximum value of the first derivative value of the smoothed sequence of calibration values; and determine at least one of a plateau characteristic and a hill point value based on a first threshold value associated with the maximum value of the estimated first derivative value; and determine that the inductive heating device operates in accordance with the determined at least one of the plateau characteristic and the hill point value. Example 27: 27. An induction heating apparatus according to example 26, wherein the induction heating apparatus comprises an inductor inductively coupleable to a susceptor for heating the aerosol-forming substrate, and a calibration value is associated with the susceptor. Example 28: An induction heating apparatus according to Example 27, comprising: a power supply for providing a DC supply voltage and a DC current; and power supply electronics connected to the power supply, the power supply electronics including a DC / AC converter, an inductor connected to the DC / AC converter for generating an alternating magnetic field when energized by alternating current from the DC / AC converter, and a controller configured to control the power provided to the power supply electronics to increase the temperature of the susceptor. Example 29: 29. The induction heating device according to example embodiment 28, wherein obtaining the sequence of calibration values ​​includes measuring a current associated with a supply electronic circuit of the induction heating device. Example 30: 30. An induction heating apparatus according to any of Examples 26-29, wherein at least one of the plateau characteristic and the hill point value corresponds to a known temperature. Example 31: An induction heating apparatus according to any of Examples 27-30, wherein the sequence of calibration values ​​includes a sequence of conductance values, and a conductance value of the sequence of conductance values ​​is associated with a calibration temperature of the susceptor. Example 32: An induction heating apparatus according to any of Examples 27-31, wherein the sequence of calibration values ​​includes a sequence of resistance values, and a resistance value of the sequence of resistance values ​​is related to a calibration temperature of the susceptor. Example 33: An induction heating apparatus according to any of Examples 27 to 32, wherein at least one of the plateau characteristic and the hill point value corresponds to the Curie temperature of the material of the susceptor. Example 34: An induction heating apparatus according to any of Examples 27-33, wherein the susceptor comprises a first susceptor material having a first Curie temperature and a second susceptor material having a second Curie temperature, the second Curie temperature being lower than the first Curie temperature, and at least one of the plateau characteristic and the hill point value corresponds to the second Curie temperature of the second susceptor material. Example 35: An induction heating device according to any of Examples 26 to 34, wherein the controller is configured to determine valley points in the sequence of smoothed calibration values ​​and calibrate the induction heating device based on the determined valley points and at least one of the determined plateau characteristics and hill point values. Example 36: An induction heating apparatus according to Example 35, wherein the valley points correspond to known temperatures. Example 37: An induction heating device according to any of Examples 26 to 36, wherein calibration is performed periodically as a recalibration during use of the induction heating device. Example 38: An induction heating apparatus according to any of Examples 26-37, further comprising a current sensor at the input side of the DC / AC converter configured to measure a DC current drawn from the power supply, and a voltage sensor at the input side of the DC / AC converter configured to measure a DC supply voltage of the power supply, wherein the sequence of calibration values ​​comprises a sequence of conductance values ​​or a sequence of resistance values, and a conductance value or resistance value associated with the susceptor is determined from the DC supply voltage of the power supply and from the DC current drawn from the power supply. Example 39: An induction heating apparatus according to Example 26, wherein the calibration value includes a conductance value, and the controller is configured to control the power provided to the power supply electronics to maintain a conductance value associated with the susceptor below at least one of a plateau characteristic and a hill point value. Example 40: 40. An aerosol generating system comprising the induction heating device according to any one of claims 26 to 39 and an aerosol-generating article, the aerosol-generating article including an aerosol-forming substrate and a susceptor.

[0028] The embodiments will now be further described with reference to the following figures: [Brief description of the drawings]

[0029] [Figure 1] FIG. 1 shows a schematic cross-sectional view of an aerosol-generating article. [Figure 2A] FIG. 2A shows a schematic cross-sectional view of an aerosol generating device for use with the aerosol-generating article shown in FIG. [Figure 2B] FIG. 2B shows a schematic cross-sectional view of an aerosol generating device that engages with the aerosol-generating article shown in FIG. [Diagram 3] FIG. 3 is a block diagram showing an induction heating device for the aerosol generating device described in relation to FIG. [Figure 4] FIG. 4 is a schematic diagram showing the electronic components of the induction heating device described in relation to FIG. [Diagram 5]FIG. 5 is a schematic diagram of an inductor of an LC load network of the induction heating device described in relation to FIG. [Figure 6] FIG. 6 is a graph of DC current versus time illustrating the remotely detectable change in electrical current that occurs as the susceptor material undergoes a phase transition associated with its Curie point. [Figure 7] FIG. 7 shows the temperature profile of the susceptor during operation of the aerosol generating device. [Figure 8] FIG. 8 is a flow chart illustrating a method for calibrating an inductive heating device for an aerosol generating system. [Figure 9A] FIG. 9A shows a classification tree that can be trained on the test recalibration curves. [Figure 9B] FIG. 9B shows a classification tree that can be trained on the test calibration curves. [Figure 10] FIG. 10 shows an example of a recalibration curve. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] 1 shows a schematic cross-sectional side view of an aerosol-generating article 100. The aerosol-generating article 100 comprises a rod of aerosol-forming substrate 110 and a downstream section 115 located downstream of the rod of aerosol-forming substrate 110. The aerosol-generating article 100 comprises an upstream section 150 located upstream of the rod of aerosol-forming substrate. The aerosol-generating article 100 thus extends from an upstream or distal end 180 to a downstream or oral end 170. In use, air is drawn through the aerosol-generating article 100 by a user from the distal end 180 to the oral end 170.

[0031] The downstream section 115 includes a support element 120 located immediately downstream of the rod of the aerosol-forming substrate, the support element 120 being longitudinally aligned with the rod 110. An upstream end of the support element 120 abuts a downstream end of the rod of the aerosol-forming substrate 110. In addition, the downstream section 115 includes an aerosol cooling element 130 located immediately downstream of the support element 120, the aerosol cooling element 130 being longitudinally aligned with the rod 110 and the support element 120. An upstream end of the aerosol cooling element 130 abuts a downstream end of the support element 120. In use, volatile material emitted from the aerosol-forming substrate 110 passes along the aerosol cooling element 130 towards the mouth end 170 of the aerosol-generating article 100. The volatile material may cool within the aerosol cooling element 130 to form an aerosol that is inhaled by the user.

[0032] The support element 120 includes 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 defines an interior cavity 145 that extends entirely from an upstream end 165 of the first hollow tubular segment 125 to a downstream end 175 of the first hollow tubular segment 125.

[0033] The aerosol cooling element 130 includes 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 defines an interior cavity 155 that extends all the way from an upstream end 185 of the second hollow tubular segment 135 to a 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 about 25 percent.

[0034] The downstream section 115 further includes a mouthpiece 140 positioned immediately downstream of the aerosol cooling element 130. As shown in the drawing in Figure 1, the upstream end of the mouthpiece 140 abuts the downstream end 195 of the aerosol cooling element 130. The mouthpiece 140 is provided in the form of a cylindrical plug of low density cellulose acetate.

[0035] The aerosol-generating article 100 further comprises an elongated susceptor 160 within the rod of the aerosol-generating substrate 110. More specifically, the susceptor 160 is disposed substantially longitudinally within the aerosol-forming substrate 110, such as generally parallel to the longitudinal axis of the rod 110. As shown in the drawing of Figure 1, the susceptor 160 is positioned at a radially central location within the rod and extends substantially along the longitudinal axis of the rod 110.

[0036] The susceptor 160 extends completely from the upstream end to the downstream end of the rod of the aerosol-forming substrate 110. In fact, the susceptor 160 has substantially the same length as the rod of the aerosol-forming substrate 110. The susceptor 160 is located in thermal contact with the aerosol-forming substrate 110, so that the aerosol-forming substrate 110 is heated by the susceptor 160 when the susceptor 160 is heated.

[0037] The upstream section 150 includes an upstream element 190 located immediately upstream of the rod of the aerosol-forming substrate 110, with the upstream element 190 being longitudinally aligned with the rod 110. The downstream end of the upstream element 190 abuts the upstream end of the rod of the aerosol-forming substrate. This advantageously prevents the susceptor 160 from becoming dislodged. Furthermore, this ensures that a consumer cannot accidentally come into contact with the heated susceptor 160 after use. The upstream element 190 is provided in the form of a cylindrical plug of cellulose acetate surrounded by a hard wrapper.

[0038] The susceptor 160 includes at least two different materials. The susceptor 160 includes at least two layers, a first layer of a first susceptor material disposed in physical contact with a second layer of a second susceptor material. The first susceptor material and the second susceptor material may each have a Curie temperature, where the Curie temperature of the second susceptor material is lower than the Curie temperature of the first susceptor material. The first material may not have a Curie temperature. The first susceptor material may be aluminum, iron, or stainless steel. The second susceptor material may be nickel or a nickel alloy.

[0039] The susceptor 160 may be formed by electroplating at least one patch of a second susceptor material onto a strip of a first susceptor material. The susceptor may be formed by coating a strip of the second susceptor material onto a strip of the first susceptor material.

[0040] The aerosol-generating article 100 shown in FIG. 1 is designed to engage with an aerosol-generating device, such as the aerosol-generating device 200 shown in FIG. 2A, to generate an aerosol. The aerosol-generating device 200 comprises a housing 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 generate an aerosol. FIG. 2B shows 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 in or near the cavity 220 (not shown) to detect a puff. The puff detector is located in or near the cavity 200 such that the puff detector is positioned along the path of the airflow when the user puffs. The puff detector may include one or more temperature detectors for detecting a temperature change in the airflow in the cavity 220, which is indicative of the user taking a puff. Additionally or alternatively, the puff detector may include a pressure sensor for detecting a reduction in airflow pressure within cavity 220, which indicates that a user is puffing.

[0041] The induction heating device 230 is shown in block diagram form in Figure 3. The induction heating device 230 comprises a DC power supply 310 and a heating arrangement 320 (also referred to as power electronics). The heating arrangement includes a controller 330, a DC / AC converter 340, a matching network 350, and an inductor 240.

[0042] The DC power supply 310 is configured to provide DC power to the heating arrangement 320. Specifically, the DC power supply 310 provides a DC supply voltage (V DC ) and DC current (I DC ) to the DC / AC converter 340. The power source 310 is preferably a battery, such as a lithium ion battery. Alternatively, the power source 310 may be another form 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 allow continuous generation of aerosol for approximately six minutes, or a multiple of six minutes. In another example, the power source 310 may have a capacity sufficient to allow a predetermined number of puffs, or discontinuous activation of the heating arrangement.

[0043] The DC / AC converter 340 is configured to supply a high frequency alternating current to the inductor 240. As used herein, the term "high frequency alternating current" refers to an alternating current having a frequency of about 500 kilohertz to about 30 megahertz. The high frequency alternating current may have a frequency of about 1 megahertz to about 30 megahertz (such as about 1 megahertz to about 10 megahertz, or about 5 megahertz to about 8 megahertz).

[0044] 4 shows diagrammatically the electrical components of the induction heating device 230, in particular the DC / AC converter 340. The DC / AC converter 340 preferably comprises a class E power amplifier. The class E power amplifier comprises a field effect transistor 420, a transistor switch 410, e.g. comprising a metal oxide semiconductor field effect transistor, a transistor switch supply circuit, indicated by arrow 430, for supplying a switching signal (gate-source voltage) to the field effect transistor 420, and an LC load network 440 comprising a series connection of a shunt capacitor C1 and a capacitor C2, corresponding to the inductor 240, and an inductor L2. Furthermore, a DC power supply 310 with a choke L1 is connected to the inductor 240 to supply a DC current I DC along with the DC supply voltage V DC The ohmic resistance R of inductor L2 is shown to supply Coil and the ohmic resistance R of the susceptor 160. Load 4. An ohmic resistance R, which represents a total ohmic load 450, is shown in more detail in FIG.

[0045] Although DC / AC converter 340 is shown as including a class E power amplifier, it should be understood that DC / AC converter 340 may use any suitable circuit for converting DC current to AC current. For example, DC / AC converter 340 may include a class D power amplifier including two transistor switches. As another example, DC / AC converter 340 may include a full-bridge power inverter having four switching transistors acting in pairs.

[0046] Returning to Figure 3, the inductor 240 may receive the AC current from the DC / AC converter 340 through a matching network 350 for optimal matching to the load, although the matching network 350 is not required. The matching network 350 may comprise a small matching transformer. The matching network 350 may improve the efficiency of the power transfer between the DC / AC converter 340 and the inductor 240.

[0047] As shown in FIG. 2A, the inductor 240 is located adjacent to the distal portion 225 of the cavity 220 of the aerosol generating device 200. Thus, during operation of the aerosol generating device 200, a high frequency alternating current supplied to the inductor 240 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 has a frequency preferably between 1 and 30 megahertz, preferably between 2 and 10 megahertz, for example between 5 and 7 megahertz. As can be seen from FIG. 2B, when the aerosol-generating article 100 is inserted into the cavity 200, the aerosol-forming substrate 110 of the aerosol-generating article 100 is located adjacent to the inductor 240 such 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 within the susceptor 160 which, as a result, is heated. Further heating is provided by magnetic hysteresis losses within the susceptor 160. The heated susceptor 160 heats the aerosol-forming substrate 110 of the aerosol-generating article 100 to a temperature sufficient to form an aerosol. The aerosol is drawn downstream through the aerosol-generating article 100 and inhaled by the user.

[0048] The controller 330 may be a microcontroller, preferably a programmable microcontroller, that is programmed to regulate the power supply from the DC power supply 310 to the induction heating arrangement 320 to control the temperature of the susceptor 160.

[0049] FIG. 6 shows the DC current I drawn from the power supply 310 over time as the temperature of the susceptor 160 (shown by the dashed line) increases. DC 6 illustrates the relationship between the DC current I and the susceptor material. More specifically, FIG. 6 illustrates the remotely detectable change in DC current I that occurs when the susceptor material undergoes a phase transition associated with its Curie point. DC is measured at the input of the DC / AC converter 340. For the purposes of this figure, the voltage V DC can be assumed to be approximately constant.

[0050] When the susceptor 160 is inductively heated, the apparent resistance of the susceptor 160 increases. This increase in resistance is proportional to the DC current I drawn from the power supply 310. DC , which at constant voltage decreases as the temperature of the susceptor 160 increases. The high frequency alternating magnetic field provided by the inductor 240 induces eddy currents near the susceptor surface, an effect known as the skin effect. The resistance of the susceptor 160 depends partly on the electrical resistivity of the first susceptor material, partly on the resistivity of the second susceptor material, and partly on the depth of the skin layers of each material available to the induced eddy currents, which resistivity depends on temperature.

[0051] When the second susceptor material reaches its Curie temperature, it loses its magnetic properties. This increases the skin layer available for eddy currents in the second susceptor material, which reduces the apparent resistance of the susceptor 160. As a result, the detected DC current I DC increases temporarily. Then, as the skin depth of the second susceptor material begins to increase, the resistance starts to decrease. This is seen as a valley (local minimum) in FIG.

[0052] As heating continues, the current continues to increase until it reaches a maximum skin depth consistent with the point at which the second susceptor material loses its natural magnetic properties. This point is called the Curie temperature and is seen in FIG. 6 as a hill (local maximum). At this point, the second susceptor material has undergone a phase change from a ferromagnetic or ferrimagnetic state to a paramagnetic state. At this point, the susceptor 160 is at a known temperature (the Curie temperature, which is a unique material specific temperature).

[0053] If the inductor 240 continues to generate an alternating magnetic field after the Curie temperature is reached (i.e., power to the DC / AC converter 340 is not interrupted), the eddy currents generated within the susceptor 160 will flow against the resistance of the susceptor 160, causing continued Joule heating of the susceptor 160, which causes the resistance to increase again (resistance has a polynomial dependence on temperature, and for most metallic susceptor materials can be approximated for our purposes to a third order polynomial dependence), and the current will begin to decrease again as long as the inductor 240 continues to supply power to the susceptor 160.

[0054] Thus, the second susceptor material, when heated through a (known) temperature range, undergoes a reversible phase transition between the valleys and hills shown in Figure 6. As can be seen from Figure 6, the apparent resistance of the susceptor 160, and therefore the onset and end of the phase transition, is dependent on the DC current I drawn from the power supply 310. DC Alternatively, the apparent resistance of the susceptor 160, and therefore the onset and end of the phase transition, can be detected remotely by monitoring the conductance value (conductance is determined by the DC current I DC DC supply voltage V DC is defined as the ratio of the DC supply voltage V DC DC current I DC The power supply 310 can be remotely detected by monitoring at least the DC current I drawn from the power supply 310. DC is monitored by the controller 330. DC is known, but the DC current I drawn from the power supply 310 DC and DC supply voltage V DC It is preferable to monitor both the DC current I DC , the conductance value, and the resistance value may be referred to as source parameters.

[0055] As the susceptor 160 heats up, a first turning point (corresponding to a local minimum in current and a local maximum in resistance) corresponds to the beginning of the phase transition, and then as the heating of the susceptor continues, a second turning point (corresponding to a local maximum in current and a local minimum in resistance) corresponds to the end of the phase transition.

[0056] Furthermore, as can be seen from FIG. 6, the apparent resistance of the susceptor 160 (and the corresponding current I drawn from the power supply 310) DC ) may vary with the temperature of the susceptor 160 in a strictly monotonic relationship over a particular temperature range of the susceptor 160 (such as between a valley and a hill). The strictly monotonic relationship allows for an unambiguous determination of the temperature of the susceptor 160 from a determination of the apparent resistance (R) or apparent conductance (1 / R). This is because each determined value of the apparent resistance represents only one value of temperature, and there is no ambiguity in the relationship. The monotonic relationship between the temperature of the susceptor 160 and the apparent resistance in the temperature range in which the second susceptor material undergoes a reversible phase transition allows for the temperature of the susceptor 160, and therefore the temperature of the aerosol-forming substrate 110, to be determined and controlled.

[0057] The controller 330 regulates the supply of power provided to the heating arrangement 320 based on the power supply parameters. The heating arrangement 320 receives a DC current I DC The heating arrangement may be provided with a current sensor (not shown) for measuring a DC supply voltage V DC A voltage sensor (not shown) may optionally be included to measure the DC current I. The current sensor and the voltage sensor are located on the input side of the DC / AC converter 340. DC , and optionally a DC supply voltage V DC is provided by a feedback channel to the controller 330 and represents the AC power P AC Controlling further supply of.

[0058] The controller 330 may control the temperature of the susceptor 160 by maintaining the measured power supply parameter value at a target value that corresponds to a target operating temperature of the susceptor 160. The controller 330 may maintain the measured power supply parameter at the target value using any suitable control loop, for example, by using a proportional-integral-derivative control loop.

[0059] Additionally, the controller 330 may maintain the temperature of the susceptor 160 below a predetermined threshold temperature by maintaining the measured conductance or current value below a predetermined threshold conductance value or by maintaining the measured resistance value above a predetermined threshold resistance value. The predetermined threshold temperature is selected to prevent overheating of the aerosol-forming substrate. If the measured power supply parameters indicate that the temperature of the susceptor exceeds the predetermined threshold temperature, the controller 330 is programmed to enter a safety mode. In the safety mode, the controller 330 is configured to perform one or more actions, such as generating an alarm (visually, and additionally or alternatively audibly) to provide an overheating warning to the user, turning off the aerosol-generating device, and preventing further use of the aerosol-generating device for a predetermined period of time.

[0060] To take advantage of the strictly monotonic relationship between the apparent resistance (or apparent conductance) of the susceptor 160 and the temperature of the susceptor 160, during user operation to generate an aerosol, a 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 susceptor material (the hill of the current plot in FIG. 6). The first calibration temperature is a temperature at or above the temperature of the susceptor at which the skin depth of the second susceptor material begins to increase, resulting in a temporary drop in resistance (the valley of the current plot in FIG. 6). Thus, the first calibration temperature is a temperature at or above the temperature at maximum permeability of the second susceptor material. The first calibration temperature is at least 50 degrees Celsius lower than the second calibration temperature. At least the second calibration value may be determined by calibration of the susceptor 160, as described in more detail below. The first calibration value and the second calibration value may be stored as calibration values ​​in a memory of the controller 330.

[0061] Since the power supply parameters have a polynomial dependence on temperature, the power supply parameters 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 ​​because the difference between the first and second calibration values ​​is small, and such that the first and second calibration values ​​are in the upper part of the operating temperature range. Thus, to adjust the temperature to the target operating temperature, the power supply parameters are adjusted according to the first and second calibration values ​​via a linear equation.

[0062] For example, if the first and second calibration values ​​are conductance values, then the target conductance value corresponding to the target operating temperature may be given as: G Target =G Lower +(x×ΔG) where ΔG is the difference between the first conductance value and the second conductance value, and x is the ratio of ΔG.

[0063] The controller 330 may control the provision of power to the heating arrangement 320 by adjusting the duty cycle of the switching transistor 410 of the DC / AC converter 340. For example, during heating, the DC / AC converter 340 continuously generates an alternating current that heats the susceptor 160 and simultaneously generates a DC current I DC and optionally a DC supply voltage V DC may be measured, preferably every 1 millisecond, for 100 milliseconds.

[0064] For example, if conductance or current is monitored by the controller 330 to adjust the susceptor temperature, the duty cycle of the switching transistor 410 is reduced when the conductance or current reaches or exceeds a value corresponding to the target operating temperature for adjusting the susceptor temperature. If resistance is monitored by the controller 330 to adjust the susceptor temperature, the duty cycle of the switching transistor 410 is reduced when the resistance reaches or falls below a value corresponding to the target operating temperature. For example, the duty cycle of the switching transistor 410 may be reduced to about 10%. In other words, the switching transistor 410 may be switched into a mode that pulses only every 10 milliseconds for a duration of 1 millisecond. During this 1 millisecond on-state (conducting state) of the switching transistor 410, the DC supply voltage V DC and the DC current I DC The value of is measured to determine the conductance. If the conductance decreases (or the resistance increases), indicating that the temperature of the susceptor 160 is below the target operating temperature, then the gate of transistor 410 is again supplied with a train of pulses at the system's selected drive frequency.

[0065] Power may be supplied to the inductor 240 by the controller 330 in the form of a successive series of pulses of current. In particular, power may be supplied to the inductor 240 in a series of pulses, each separated by a time interval. The successive series of pulses may include two or more heating pulses and one or more probing pulses between the successive heating pulses. The heating pulses have an intensity such that they heat the susceptor 160. The probing pulses are separate power pulses that do not heat the susceptor 160, but rather have an intensity such that they obtain feedback on the evolution (decrease) of the power supply parameters and then the susceptor temperature. The controller 330 may control the power by controlling the duration of the time interval between successive heating pulses of power supplied to the inductor 240 by the DC power supply. Additionally or alternatively, the controller 330 may control the power by controlling the length (in other words, the duration) of each of the successive heating pulses of power supplied to the inductor 240 by the DC power supply.

[0066] The controller 330 is programmed to perform a calibration process to obtain calibration values ​​in which the power supply parameters are measured at known temperatures of the susceptor 160. The known temperatures of the susceptor may be a first calibration temperature corresponding to the first calibration value and a second calibration temperature corresponding to the second calibration value. The calibration process is performed each time a 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 a user turns on the aerosol generating device. The controller 330 may be programmed to enter a calibration mode each time a user inserts an aerosol-generating article 100 into the aerosol generating device 200. Thus, the calibration process is performed during a first heating phase of the aerosol generating device prior to user operation of the aerosol generating device 200 to generate an aerosol.

[0067] During the calibration process, the controller 330 controls the DC / AC converter 340 to continuously or intermittently supply power to the inductor 240 to heat the susceptor 160. The controller 330 controls the current I drawn by the power supply. DC , and optionally, the supply voltage V DC The power supply parameters are monitored by measuring the current flow rate (Vp) of the susceptor 160. As described above in connection with FIG. 6, as the susceptor 160 heats up, the measured current decreases until a first turning point is reached and the current increases. This first turning point corresponds to a local minimum conductance or current value (local maximum resistance value). The controller 330 may record the power supply parameters at the first turning point as a first calibration value.

[0068] The conductance or resistance is determined by the measured current I DC and the measured voltage V DC Alternatively, the supply voltage V DC may be assumed to be approximately constant. The temperature of the susceptor 160 at the first calibration value is referred to as the first calibration temperature. The first calibration temperature is preferably between 150 degrees Celsius and 350 degrees Celsius. More preferably, when the aerosol-forming substrate 110 includes 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.

[0069] As the controller 330 continues to control the power provided by the DC / AC converter 340 to the inductor 240, the controller 330 continues to monitor the power source parameter until a second turning point is reached. The second turning point corresponds to a maximum current (corresponding to the Curie temperature of the second susceptor material) before the measured current begins to decrease. This turning point corresponds to a local maximum conductance or current value (local minimum resistance value). The controller 330 records the power source parameter value at the second turning point as a second calibration value. The temperature of the susceptor 160 at the second calibration value is referred to as 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 / AC converter 340 to interrupt the provision of power to the inductor 240, resulting in a decrease in the temperature of the susceptor 160 and a corresponding decrease in the measured current.

[0070] This process of continuously heating the susceptor 160 to obtain the first and second calibration values ​​due to the shape of the graph may be repeated at least once during the calibration mode. After interrupting the provision of power to the inductor 240, the controller 330 continues to monitor the power source parameter until a third turning point is observed. The third turning point corresponds to a second minimum conductance or current value (second maximum resistance value). Once the third turning point is detected, the controller 330 controls the DC / AC converter 340 to continuously provide power to the inductor 240 until a fourth turning point of the monitored power source parameter is observed. The fourth turning point corresponds to a second maximum conductance or current value (second minimum resistance value). The controller 330 stores the power source parameter value measured at the third turning point as the first calibration value and stores the power source parameter value measured at the fourth turning point as the second calibration value. The repetition of the measurement of turning points corresponding to the minimum and maximum measured current significantly improves subsequent temperature regulation during user operation of the device to generate an aerosol. Preferably, the controller 330 adjusts the power based on the power supply parameter value obtained from the second maximum and second minimum values, which is more reliable since heat requires more time to disperse within the aerosol-forming substrate 110 and the susceptor 160.

[0071] Furthermore, during the first heating stage, to further improve the reliability of the calibration process, the controller 310 may be optionally programmed to perform a pre-heating process prior to the calibration process. For example, if the aerosol-forming substrate 110 is particularly dry or in similar conditions, the calibration may be performed before heat spreads into the aerosol-forming substrate 110, reducing the reliability of the calibration value. If the aerosol-forming substrate 110 is wet, the susceptor 160 will take longer to reach the valley temperature (depending on the moisture content of the substrate 110).

[0072] 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 the increasing temperature of the susceptor 160 until a turning point corresponding to a minimum measured current is reached. At this stage, the controller 330 is configured to wait a predetermined period of time to allow the susceptor 160 to cool before continuing the heating. Thus, the controller 330 controls the DC / AC converter 340 to interrupt the supply of power to the inductor 240. After the predetermined period of time, the controller 330 controls the DC / AC converter 340 to provide power until a turning point corresponding to a minimum measured current is again reached. At this point, the controller controls the DC / AC converter 340 to again interrupt the supply of power to the inductor 240. The controller 330 again waits the same predetermined time to allow the susceptor 160 to cool before continuing the heating. This heating and cooling of the susceptor 160 is repeated for the predetermined duration of the preheating process. The predetermined duration of the preheating process is preferably 11 seconds. Following the pre-heating process, the calibration process is preferably for a predetermined combined duration of 20 seconds.

[0073] If the aerosol-forming substrate 110 is dry, the first current minimum of the pre-heating process is reached within the predetermined time and the interruption of power is repeated until the end of the predetermined time. If the aerosol-forming substrate 110 is wet, the first current minimum of the pre-heating process is reached towards the end of the predetermined time. Thus, carrying out the pre-heating process for a predetermined duration ensures that, regardless of the physical state of the substrate 110, the substrate 110 has enough time to reach a minimum operating temperature in order to be ready to continue to apply power to reach the first maximum. This allows for calibration as early as possible without the risk that the substrate 110 has not yet reached the valley.

[0074] Furthermore, the aerosol-generating article 100 may be configured such that the current minimum is always reached within a predetermined duration of the pre-heating process. If the current minimum is not reached within a predetermined duration of the pre-heating process, this may indicate that the aerosol-generating article 100, including the aerosol-forming substrate 110, is not suitable for use with the aerosol-generating device 200. For example, the aerosol-generating article 100 may include 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 arrangement 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 stop operation of the aerosol-generating device 200.

[0075] As mentioned above, as a first step in the calibration process, the pre-heating process may be performed in response to receiving a user input, such as, for example, a user activation of the aerosol generating device 200. Additionally or alternatively, the controller 330 may be configured to detect the presence of an aerosol-generating article 100 in the aerosol generating device 200, and the pre-heating process may be performed in response to detecting the presence of the aerosol-generating article 100 in the cavity 220 of the aerosol generating device 200.

[0076] During user operation of the aerosol generating device 200 to generate an aerosol (referred to as the second heating stage), the apparent conductance (apparent resistance) values ​​at the hills and valleys shown in Figure 6 drift over time. This is because the apparent resistance of the susceptor is proportional to the ohmic resistance R of the inductor L2, as shown in Figure 5. coil and the ohmic resistance R of the susceptor 160. load Therefore, changes in the temperature of the inductor L2 during operation of the device 200 may affect the apparent resistance. Therefore, the calibration value measured during the calibration process in the first heating stage will drift during operation of the aerosol generation device 200.

[0077] During normal operation when the aerosol generating device 200 is generating an aerosol, the controller 330 operates in a heating mode to heat the aerosol-forming substrate. From the heating mode, the controller 330 may be programmed to enter a recalibration mode to perform a further repetition of at least a portion of the calibration process at a predetermined interval during user operation of the aerosol generating device 200 to generate an aerosol. The predetermined interval may be a predetermined time interval or a predetermined number of puffs. Additionally or alternatively, the controller 330 may be programmed to enter the recalibration mode to repeat at least a portion of the calibration process in response to detection of the completion of a puff. The calibration process may take between 200 milliseconds and 2 seconds to perform.

[0078] Performing further iterations of at least a portion of the calibration process may include re-measuring both calibration values ​​at both turning points (shown as hills and valleys in FIG. 6) or re-measuring only the calibration value at one of the turning points, e.g., a local maximum of current or conductance (local minimum of resistance).

[0079] To perform a further iteration of the calibration process (in other words, to perform a recalibration), the controller 330 reduces the current drawn by the power supply I DC , and optionally the supply voltage V DC The power supply parameters associated with the susceptor 160 are monitored by measuring the measured current I as the susceptor 160 heats up during further iterations of the calibration process because the minimum operating temperature of the aerosol generating device is greater than the first calibration temperature. DC reaches a tipping point and the current I DC begins to decrease. This turning point corresponds to the end of the reversible phase transition of the susceptor 160, observed as a local maximum conductance or current value (local minimum resistance value). The controller 330 records the power supply parameter value at the turning point as the re-measured second calibration value.

[0080] Upon reaching the first turning point, the controller 330 controls the DC / AC converter 340 to reduce the power provided to the inductor 240 to allow the susceptor 160 to cool down. For example, the controller 330 may reduce the duty cycle of the DC / AC converter 340 to 10%. The controller 330 may reduce the power provided to the inductor 240 until the susceptor 160 reaches its respective target operating temperature at which point the controller 300 resumes normal operation in the heating mode.

[0081] Alternatively, the controller 330 may continue to decrease the power provided to the inductor 240 until another turning point is observed. This other turning point corresponds to an end of the reversible phase transition of the susceptor, observed as a local minimum conductance or current value (local maximum resistance value). The controller 330 records the power supply parameter value at the other turning point as the 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 further iteration of the calibration process.

[0082] FIG. 7 is a graph of conductance versus time illustrating a heating profile of the susceptor 160. The graph illustrates two successive stages of heating, a first heating stage 710 including the preheating process 710A and the calibration process 710B described above, and a second heating stage 720 corresponding to user operation of the aerosol generating device 200 to generate an aerosol. As described above, during the first heating stage 710, the controller 330 operates in a calibration mode. Once the calibration is complete, the controller enters a heating mode and may periodically switch to a recalibration mode during the second heating stage 720. It should be understood that FIG. 7 is not drawn to scale. Specifically, the first heating stage 710 has a shorter duration than the second heating stage 720. For example, the first heating stage 710 may have a duration of 5 seconds to 30 seconds, preferably 10 to 20 seconds. The second heating stage 720 may have a duration of 140 to 340 seconds.

[0083] 7 is illustrated as a graph of conductance versus time, it should be understood that the controller 330 may be configured to control the heating of the susceptor 160 during the first heating stage 710 and the second heating stage 720 based on a measured resistance or current, as described above. Indeed, while the techniques for controlling the heating of the susceptor during the first heating stage 710 and the second heating stage 720 have been described above based on a determined conductance value or a determined resistance value associated with the susceptor, it should be understood that the techniques described above may be implemented based on a value of current measured at the input of the DC / AC converter 340.

[0084] As can be seen from FIG. 7, the second heating stage 720 includes a number of conductance steps corresponding to a number of temperature steps 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 such that aerosol is formed during each temperature step. The first operating temperature of the susceptor is preferably the lowest temperature at which the aerosol-forming substrate forms aerosol in a volume and amount sufficient to provide a satisfactory experience when inhaled by a user. The second operating temperature of the susceptor is the highest temperature to which it is desired to heat the aerosol-forming substrate in order for a user to inhale the aerosol.

[0085] The first operating temperature of the susceptor 160 is equal to or greater than a first calibrated temperature of the susceptor 160 corresponding to a first calibrated value (a valley in the current plot shown in FIG. 6). The first operating temperature may be between 150 degrees Celsius and 330 degrees Celsius. The second operating temperature of the susceptor 160 is equal to or less than a second calibrated temperature of the susceptor 160 corresponding to a second calibrated value (a hill in the current plot in FIG. 6) at the Curie temperature of the second susceptor material. The second operating temperature may be between 200 degrees Celsius and 400 degrees Celsius. The difference between the first operating temperature and the second operating temperature is at least 50 degrees Celsius.

[0086] It should be understood that the number of temperature steps shown in FIG. 7 is exemplary and the second heating stage 720 includes at least three consecutive temperature steps, preferably two to fourteen temperature steps, and most preferably three to eight temperature steps. Each temperature step may have a predetermined duration. The duration of the first temperature step is preferably longer than the duration of the subsequent temperature steps. The duration of each temperature step is preferably longer than 10 seconds, preferably between 30 seconds and 200 seconds, more preferably between 40 seconds and 160 seconds. The duration of each temperature step may correspond to a predetermined number of user puffs. Preferably, the first temperature step corresponds to four user puffs and each subsequent temperature step corresponds to one user puff.

[0087] For the duration of each temperature step, the temperature of the susceptor 160 is maintained at the target operating temperature corresponding to the respective temperature step. Thus, during the duration of each temperature step, the controller 330 controls the provision of power to the heating arrangement 320 such that the measured power supply parameter is maintained at a target value corresponding to the target operating temperature of the respective temperature step, the target value being determined with reference to the first and second calibration values ​​as described above.

[0088] As an example, the second heating stage 720 has five temperature steps, a duration of 160 seconds, and a G Target =G Lower A first temperature step 720a with a target conductance value of +(0.09×ΔG), duration of 40 seconds and G Target =G Lower A second temperature step 720b with a target conductance value of +(0.25×ΔG), duration of 40 seconds and G Target =G Lower A third temperature step 720c with a target conductance value of +(0.4×ΔG), duration of 40 seconds and G Target =G Lower A fourth temperature step 720d having a target conductance value of +(0.56×ΔG) and a duration of 85 seconds and G Target =G LowerA fifth temperature step 720e may be included having a target conductance value of +(0.75×ΔG). These temperature steps may correspond to temperatures of 330 degrees Celsius, 340 degrees Celsius, 345 degrees Celsius, 355 degrees Celsius, and 380 degrees Celsius.

[0089] Thus, control of the operating temperature of the susceptor 160 to generate the aerosol 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 drift of the apparent conductance of the susceptor over the duration of the second heating stage 720 means that for the same susceptor temperature, the value of the apparent conductance decreases over the duration of the second heating stage 720. Therefore, to be able to precisely control the susceptor temperature, as well as to prevent overheating of the aerosol-forming substrate 110, the controller 330 is programmed to periodically enter a recalibration mode to repeat at least a portion of the calibration process during the second heating stage 720. For example, at least a portion of the calibration process is repeated every 15 seconds to 2 minutes. Preferably, at least a portion of the calibration process is repeated every 30 seconds. This is illustrated in FIG. 8, which shows the second heating stage 720 in more detail, including the recalibration between each of the temperature steps. Also, 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 further iterations of the calibration process shown in FIG. 8. Optionally, the first calibration value is re-measured during further iterations of the calibration process. The target power supply parameter value corresponding to each temperature step may be stored in the memory of the controller 330 and updated after each iteration of the calibration process. The controller 330 may adjust the target power supply parameter value for each 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 may adjust the target power supply parameter value for each temperature step based on the re-measured first calibration value. Additionally or alternatively, the controller 330 may adjust the target power supply parameter value for each temperature step based on a combination of one or more calibration values ​​measured during the first heating stage 710 and one or more calibration values ​​measured during at least one further iteration of the calibration process during the second heating stage 720.

[0090] Thus, in the above example, for the first temperature step 720a, the target conductance is, at least initially, at the start of the heating mode, the calibration value G obtained during the calibration process 710B of the first heating phase 710. Lower and ΔG. Assuming the controller 330 is programmed to repeat the calibration process every 30 seconds, the calibration process is repeated five times during the first temperature step, after 30, 60, 90, 120, and 150 seconds. The calibration process is repeated once during the second temperature step 720b, after 180 seconds (20 seconds after the start of the second temperature step). The calibration process is 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 is repeated once during the fourth temperature step 720d, after 280 seconds (30 seconds after the start of the third temperature step). The calibration process is 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 determines whether or not G is a positive integer based at least in part on at least one of the calibration values ​​resulting from the most recent additional iteration of the calibration process. Target For example, the target conductance after each recalibration is adjusted by adjusting the remeasured calibration value G obtained during the respective recalibration process. Lower i and ΔG i or based at least in part on the calibration value G Lower and the remeasured values ​​ΔG obtained during each recalibration process. i where i=start time of the second heating stage 720+30 seconds.

[0091] During the second heating phase 720, the user draws the aerosol generated by the aerosol generating device into his body. In other words, the user puffs on the mouthpiece 140 of the aerosol generating article, which is partially received in the aerosol generating device 200. As the user puffs, cool air is drawn through the aerosol generating article 100 into the aerosol generating device 200, thereby cooling the susceptor 160. Thus, if a recalibration is performed during a puff, the temporary cooling of the susceptor 160 has the effect of temporarily reducing the difference between the calibration values ​​(e.g., reducing the value of ΔG). In other words, referring again to FIG. 6, there is a temporary decrease in the value of the current at the hills and a temporary increase in the value of the current at the valleys for the duration of the puff. Thus, the calibration value measured during the user puff is not accurate. In particular, if the calibration value obtained during the puff is used to control the temperature of the susceptor 160, there is a risk of overheating the susceptor 160, which would result in the release of undesirable aerosol components. Therefore, the controller 330 is programmed so that the recalibration does not overlap with a puff.

[0092] The induction heating device may be a handheld induction heating device. The induction heating device may be limited in terms of the number or size of 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.

[0093] The induction heating device or a controller associated with the induction heating device may be configured to obtain the conductance values ​​and process these conductance values ​​to calibrate the induction heating device. The relationship between the conductance values ​​and the temperature of the susceptor may be known for at least one time point. For example, the temperature for at least one of the plateau characteristics and hill point values ​​of the calibration curve of the conductance values ​​may be known. Thus, the calibrated induction heating device may avoid exceeding the Curie temperature of the susceptor. The Curie temperature may be the temperature at which the susceptor loses its permanent magnetism.

[0094] Calibration may include determining valley points of a calibration curve, which may be referred to as an S-curve, and / or hill points and plateau characteristics of the calibration curve. The calibration curve may include at least one of a minimum, an inflection point, and a maximum and / or plateau characteristics.

[0095] The first characteristic point of the calibration curve may be a minimum of 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 a hill point where the power supplied to the induction heating device is gradually reduced to avoid overheating. The detection of the minimum, which may also be referred to herein as a valley or valley point, can be performed by different methods known in the art. However, it may be difficult to determine the maximum or plateau characteristic of the calibration curve.

[0096] As discussed above, the first and second calibration values ​​may be determined based on at least one of the determined plateau characteristic and hill point value.

[0097] It is therefore desirable to provide an improved method for reliably determining the maximum or plateau characteristics of a calibration curve in a fast and efficient manner. Given the small processing power of induction heating devices, it is desirable to keep the numerical operations as simple as possible. Furthermore, it is desirable to detect overheating or determine the maximum or plateau characteristics of a calibration curve in less than 200 ms.

[0098] Calibration may refer to one of two types of curves, including calibration curves and recalibration curves. A calibration curve may begin with a well-defined valley and then gradually increase for a duration of several seconds until it reaches the plateau characteristic of the calibration curve. A recalibration curve may not include a valley before the increase and is shorter, its duration may be as short as 300 ms until it reaches the plateau characteristic of the calibration curve.

[0099] 8 is a flow diagram illustrating a method 800 for determining a plateau characteristic or hill point for calibrating an inductive heating device for an aerosol generating system. The method includes, at step 810, obtaining a sequence of calibration values ​​for the inductive heating device for the aerosol generating system. The sequence of calibration values ​​is associated with a calibration curve. As described above, the controller 330 may be programmed to implement the method 800.

[0100] In 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 a (semi-)Gaussian kernel G of standard deviation σ to denoise it.

[0101] A first derivative of the sequence of smoothed calibration values ​​is determined in step 830. The first derivative may be determined using the following property of convolution:

number

number

[0102] A first derivative value of the sequence of smoothed calibration values ​​may be determined every millisecond. The first derivative value of the sequence of smoothed calibration values ​​may be determined as follows: Determining the smoothed derivative value:

number

[0103] In step 840, the maximum of the first derivative of the sequence of smoothed calibration values ​​is estimated. The shape of the calibration curve, including inflection points and plateau characteristics, ensures that Z has a maximum that can be robustly detected. The maximum of Z(t) is at time tmax and is estimated by determining the time when Z(tmax) falls below the average of nmax previous steps. nmax may indicate the number of time steps used to robustly detect the maximum.

[0104] At step 850, at least one of the plateau characteristics and the hill point value is determined based on a first threshold value associated with the maximum value of the estimated first derivative value. For example, the search for at least one of the plateau characteristics and the hill point value may begin to decrease Z(t) once the maximum value falls below p1·Z(tmax) (at tp1) again. p1 may define the fraction of Z(tmax) at which Z(t) must begin to search for at least one of the plateau characteristics and the hill point value. For example, p1 may be 0.1 for the calibration curve and 0.2 for the recalibration curve. At least one of the plateau characteristics and the hill point value may be determined as follows: Start time for detection of maximum value and plateau detection of Z(t):

number

[0105] Heating of the induction heating device may be stopped in response to determining at least one of the plateau characteristic and the hill point value such that the induction heating device does not heat beyond a temperature associated with at least one of the plateau characteristic and the hill point value. A first stopping criterion may be achieved at a time tstop, where Z(t stop <=p stop 1·Z(t max ). pstop1 may define the fraction of Z(tmax) for which Z(t) is the first stopping criterion.

[0106] In step 860, heating by the induction heating device may be stopped when the first derivative of the sequence of smoothed calibration values ​​increases again after a maximum value of the first derivative of the sequence of smoothed calibration values. For example, the second stopping criterion may be a robust criterion MA nstop2 (Z)(t)>MA (t-ta)·1e 3 The regrowth pattern of Z(t) is determined by checking whether 80% of nstop2 consecutive steps using (Z)(t) are regrowths. p1 This can be achieved when the MA n (x) is the n-term moving average (convolution) of x. n (x) is the n-term running median for x. nstop2 may define the smoothing kernel size for applying the second stopping criterion.

[0107] The determination of whether to stop heating by the induction heating device may be performed as follows: Stopping requirements:

number

[0108] Steps 810 to 860 may be repeated periodically, for example every 10 ms.

[0109] At step 870, the induction heating device is operated in accordance with at least one of the determined plateau characteristics and hill point values. Operating the induction heating device in accordance with at least one of the determined plateau characteristics and hill point values ​​may include maintaining a temperature associated with the aerosol generation system below a particular temperature based on the determined plateau characteristics and at least one of the hill point values.

[0110] The 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 being heated. Thus, calibrations for different calibration curves may last for different times, which may affect the level of smoothing required to detect the feature points of the calibration curve. A recalibration may be shorter than a calibration. A recalibration curve may have a steeper slope compared to the calibration curve. For example, a recalibration may be performed in 300 ms until at least one of a plateau characteristic and a hill point value is determined.

[0111] Prediction of the duration of such curves can be done by machine learning using the time derivatives as input.

[0112] The derivatives (or their approximations) may serve as learning features and may be used to smooth the curve. 10 The characteristic may be calculated directly from the conductance of the first 38 ms using t i >t vally +10 -2 For +2, it can be calculated as follows:

number

[0113] The method 800 may autoscale at least one parameter used to determine at least one of the plateau characteristics and the hill point value. For example, at step 802, the type of the calibration curve may be determined by classifying the calibration curve. The calibration curve may be classified based on a slope of the calibration curve. The type may 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 type of the calibration curve may be determined based on a second threshold associated with a maximum value of a first derivative value of the sequence of estimated smoothed calibration values.

[0114] At step 804, at least one parameter for the calibration may be selected based on the determined type of calibration curve. The at least one parameter may include at least one of a first parameter specifying a first threshold value for determining at least one of a plateau characteristic and a hill point value, a second parameter specifying a smoothing of the sequence of calibration values, a third parameter specifying a number of consecutive values ​​of the first derivative value of the smoothed sequence of calibration values ​​used in estimating a maximum value of the first derivative value, a fourth parameter specifying a number of consecutive values ​​of the first derivative value of the smoothed sequence of calibration values ​​used in determining at least one of a plateau characteristic and a hill point value, and a fifth parameter specifying a number of values ​​of the first derivative value of the smoothed sequence of calibration values ​​used in determining a re-increase of the first derivative value of the smoothed sequence of calibration values ​​after a maximum value of the first derivative value of the smoothed sequence of calibration values. The second threshold value may define a fraction of the maximum value of the first derivative value of the sequence of smoothed calibration values.

[0115] The recalibration curve is the approximate time t=t max Based on a threshold associated with , the recalibration curve may be classified as "short-R" or "long-R". Figure 9A shows a classification tree that may be trained on the test recalibration curve. The classification tree is a tree of depth 1.

[0116] The calibration curve is the approximate time t=t max Based on a threshold associated with , the classification tree may be classified as "short-C", "medium-C", or "long-C". Figure 9B shows a classification tree that may be trained on the test calibration curve. The classification tree may be a tree of depth 2.

[0117] Alternatively, the recalibration and calibration curves may be classified based on a threshold value indicative of the slope of the calibration curve, for example, the average value of the calibration curve at a particular time after the valley point may be compared to the threshold value.

[0118] Based on the prediction category, the prediction category may be used to select a predefined set of parameters by knowing if the curve is a calibration curve. To reduce the computation time, Z(t m ) may be calculated every 2 ms (m=1, 3, 5, 7, ..., 2n-1, ...),

number

number

number

[0119] In the experiment, the relative and absolute difference between the conductance at the stop time and the expected maximum conductance was calculated. The relative difference between the maximum conductance and the detected maximum was calculated against a calibration curve, if c=valley exists.

number

number

[0120] An example of a recalibration curve 1010 is shown in Figure 10. Figure 10 also shows the determined hill point value 1020 and the point 1030 that meets the second stopping criterion.

[0121] For the purposes of this specification and the appended claims, unless otherwise indicated, all numbers expressing amounts, quantities, percentages, and the like should be understood in all instances to be modified by the term "about." Also, all ranges include the maximum and minimum points disclosed, and include any intermediate ranges therein, which may or may not be specifically recited herein. Within this context, the number A may be considered to include a numerical value that is within the general standard error for the measurement of the property that the number A modifies. The number A may deviate by the percentages recited above, in some cases as used in the appended claims, provided that the amount by which A deviates does not materially affect the basic and novel properties of the claimed invention. Also, all ranges include the maximum and minimum points disclosed, and include any intermediate ranges therein, which may or may not be specifically recited herein.

Claims

1. 1. A method for calibrating an induction heating device for an aerosol generating system, the method being carried out by a controller, comprising: obtaining a sequence of calibration values ​​for an induction heating device for an aerosol-generating system, the sequence of calibration values ​​being associated with a calibration curve, the induction heating device including an inductor configured to be coupled to a susceptor to heat an aerosol-forming substrate, the sequence of calibration values ​​including one of a sequence of conductance values ​​and a sequence of resistance values, and values ​​of the sequence of calibration values ​​being associated with a calibration temperature of the susceptor; 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 plateau characteristic and a hill point value based on a first threshold associated with the maximum value of the estimated first derivative; and operating the induction heating device in accordance with at least one of the determined plateau characteristics and hill point values.

2. The method of claim 1 , wherein the smoothing the sequence of calibration values ​​and the determining the first derivative of the smoothed sequence of calibration values ​​are performed in a single calculation.

3. 3. The method of claim 1, wherein estimating the maximum value of the first derivative value of the sequence of smoothed calibration values ​​comprises comparing the value of the first derivative value of the sequence of smoothed calibration values ​​with a predetermined number of values ​​of the first derivative value of the sequence of smoothed calibration values.

4. 3. The method of claim 1, wherein the value of the first derivative value of the sequence of smoothed calibration values ​​is estimated as the maximum value when an average of a predetermined number of previous values ​​of the first derivative value of the sequence of smoothed calibration values ​​is higher than the value of the first derivative value of the sequence of smoothed calibration values.

5. 3. The method of claim 1, wherein the first threshold is a fraction of the maximum value of the first derivative of the sequence of smoothed calibration values.

6. 3. The method of claim 1, further comprising: stopping heating of the induction heating device when the first derivative value of the sequence of smoothed calibration values ​​increases again after the maximum value of the first derivative value of the sequence of smoothed calibration values.

7. 7. The method of claim 6, wherein the re-increase of the first derivative value of the sequence of smoothed calibration values ​​after the maximum value of the first derivative value of the sequence of smoothed calibration values ​​is determined when an average of a certain number of consecutive values ​​of the first derivative value increases over time.

8. determining a type of the calibration curve by classifying the calibration curve; The method of claim 1 , further comprising: selecting at least one parameter for the calibration based on the determined type of calibration curve.

9. The method of claim 8 , wherein the calibration curves are classified based on the slope of the calibration curve.

10. The method of claim 1 or 2, further comprising: ceasing heating of the induction heating device in response to determining the at least one of the plateau characteristic and hill point value.

11. 1. An induction heating device for an aerosol generating system, the induction heating device comprising: obtaining a sequence of calibration values ​​for the induction heating device, the sequence of calibration values ​​being related to 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 plateau characteristic and a hill point value based on a first threshold associated with a maximum value of the estimated first derivative; the induction heating device is operated in accordance with at least one of the determined plateau characteristics and hill point values; The induction heating device includes an inductor configured to be coupled to a susceptor to heat an aerosol-forming substrate, the sequence of calibration values ​​includes one of a sequence of conductance values ​​and a sequence of resistance values, and values ​​of the sequence of calibration values ​​are associated with a calibration temperature of the susceptor.

12. The induction heating device is a power supply for providing a DC supply voltage and a DC current; a power supply electronic circuit connected to the power source, the power supply electronic circuit comprising: DC / AC converters, the inductor, connected to the DC / AC converter to generate an alternating magnetic field when energized by an alternating current from the DC / AC converter; and and power electronics including the controller, the controller configured to control the power provided to the power electronics to increase the temperature of the susceptor.

13. 13. The induction heating device of claim 12, wherein obtaining the sequence of calibration values ​​includes measuring a current associated with the supply electronics of the induction heating device.

14. An aerosol-generating system comprising: the induction heating device according to any one of claims 11 to 13; and an aerosol-generating article, wherein the aerosol-generating article includes the aerosol-forming substrate and the susceptor.

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