WO2023166150A1

WO2023166150A1 - Smoking device with dynamic heating profile

Info

Publication number: WO2023166150A1
Application number: PCT/EP2023/055375
Authority: WO
Inventors: Fabrice STEFFEN; Jerome Uthurry
Original assignee: Philip Morris Products S.A.
Priority date: 2022-03-03
Filing date: 2023-03-02
Publication date: 2023-09-07

Abstract

A method is provided of operating an aerosol-generating device for generating aerosol from an aerosol-forming substrate during a usage session. The aerosol-generating device comprises a power supply arranged to supply power to a heater to control temperature of the heater during the usage session, and control electronics. The method comprises steps of determining a target operating temperature for the heater, the target operating temperature being determined with reference to a) a cumulative value of a user interaction parameter monitored during the usage session, and b) time elapsed from a trigger event; and using the target operating temperature to control temperature of the heater.

Description

SMOKING DEVICE WITH DYNAMIC HEATING PROFILE

The present disclosure relates to a method of operating an aerosol-generating device, a computer-readable medium for use in an aerosol-generating device, an aerosol-generating device, as well as an aerosol-generating system.

Aerosol-generating devices configured to generate an aerosol from an aerosol-forming substrate, such as a tobacco-containing substrate, are known in the art. Typically, an inhalable aerosol is generated by the transfer of heat from a heat source to a physically separate aerosolforming substrate or material, which may be located within, around or downstream of the heat source. An aerosol-forming substrate may be a liquid substrate contained in a reservoir. An aerosol-forming substrate may be a solid substrate. An aerosol-forming substrate may be a component part of a separate aerosol-generating article configured to engage with an aerosolgenerating device to form an aerosol. During consumption, volatile compounds are released from the aerosol-forming substrate by heat transfer from the heat source and entrained in air drawn through the aerosol-generating article. As the released compounds cool, they condense to form an aerosol that is inhaled by the consumer.

Some aerosol-generating devices are configured to provide user experiences that have a finite duration. The duration of a usage session may be limited, for example, to approximate the experience of consuming a traditional cigarette. Some aerosol-generating devices are configured to be used with separate, consumable, aerosol-generating articles. Such aerosol-generating articles comprise an aerosol-forming substrate or substrates that are capable of releasing volatile compounds that can form an aerosol. Aerosol-forming substrates are commonly heated to form an aerosol. As the volatile compounds in an aerosol-forming substrate are depleted, the quality of the aerosol produced may deteriorate. Thus, some aerosol-generating devices are configured to limit the duration of the usage session to help prevent generation of a lower quality aerosol from a substantially depleted aerosol-forming substrate of an aerosol-generating article. A user would inhale aerosol from such a known aerosol-generating device by the application of one or more puffs to the device during the usage session. Some known aerosol-generating devices may limit the duration of the usage session based upon when a number of puffs applied to the device in the session reaches a predetermined limit.

It is known to provide power to a heat source to heat an aerosol-forming substrate in accordance with a thermal profile which varies over the duration of a usage session. In effect, such known thermal profiles define a temperature variation for the heat source as a function of the time elapsed in the usage session. As an aerosol-forming substrate becomes more depleted during a usage session, more energy is required to extract the remaining volatile compounds of the substrate which form the aerosol. Thus, it is known to use a thermal profile which increases a target operating temperature for the heat source over the second half of a usage session. Known thermal profiles used in the operation of a heat source are based on an idealised, hypothetical usage session. The idealised usage session may be characterised by a predetermined length for the usage session. The idealised usage session may additionally be based upon an assumed or idealised puffing behaviour of a user; for example, on an assumption that successive puffs are applied at a predetermined rate over a finite period of time. However, when a real-life usage session departs from the assumptions inherent in the idealised usage session, the use of such known thermal profiles to control the temperature of the heat source can lead to inefficient extraction of aerosol from the substrate and be detrimental to the overall user experience. By way of example, if a user applied puffs at a faster rate than assumed in the known thermal profile, this could result in the usage session being terminated earlier than anticipated in the idealised usage session. Consequently, the temperature of the heat source may never reach the levels required in the second half of the usage session to efficiently extract aerosol from the substrate. It is therefore desired to overcome the deficiencies and limitations outlined above.

According to a first aspect of the present invention, there may be provided a method of operating an aerosol-generating device for generating aerosol from an aerosol-forming substrate during a usage session. The aerosol-generating device may comprise a power supply arranged to supply power to a heater to control temperature of the heater during the usage session, and control electronics. The method may comprise the step of determining a target operating temperature for the heater. The target operating temperature may be determined with reference to a) a cumulative value of a user interaction parameter monitored during the usage session, and b) time elapsed from a trigger event. The target operating temperature may be used to control temperature of the heater. Preferably, the target operating temperature is determined to have an initial value on detection of the trigger event. The target operating temperature may vary from the initial value at a first rate of change during a first period of the time elapsed, the first period of time extending between the trigger event and a first time threshold, and at a second rate of change, different from the first rate of change, during a second period of the time elapsed, the second period extending between the first time threshold and a second time threshold occurring after the first time threshold.

In a preferred embodiment, the aerosol-generating device comprises a power supply arranged to supply power to a heater to control temperature of the heater during the usage session, and control electronics, the method comprising the steps of; determining a target operating temperature for the heater, the target operating temperature being determined with reference to a) a cumulative value of a user interaction parameter monitored during the usage session, and b) time elapsed from a trigger event, and using the target operating temperature to control temperature of the heater, in which the target operating temperature is determined to have an initial value on detection of the trigger event, the target operating temperature varying from the initial value at a first rate of change during a first period of the time elapsed, the first period of time extending between the trigger event and a first time threshold, and at a second rate of change, different from the first rate of change, during a second period of the time elapsed, the second period extending between the first time threshold and a second time threshold occurring after the first time threshold.

In a further preferred embodiment, the method may be a method of operating an aerosolgenerating device for generating aerosol from an aerosol-forming substrate during a usage session, the usage session having a usage session start and a usage session end, the aerosolgenerating device comprising: a power supply arranged to supply power to a heater to control temperature of the heater during the usage session, and control electronics including at least one microprocessor and at least one memory, the control electronics configured to detect and record user puffs taken during the usage session, the method comprising steps of: determining a target operating temperature for the heater, the target operating temperature being determined with reference to a) a cumulative value of user puffs detected during the usage session, and b) time elapsed from a trigger event, the trigger event being an immediately preceding user puff; and using the target operating temperature to control temperature of the heater, in which, the target operating temperature is determined to have an initial value on detection of the trigger event, and in which the operating temperature varies from the initial value at a first rate of change during a first period of the time elapsed, the first period of time extending between the trigger event and a first time threshold, and at a second rate of change, different from the first rate of change, during a second period of the time elapsed, the second period extending between the first time threshold and a second time threshold occurring after the first time threshold, and optionally at a third rate of change, different from the second rate of change, during a third period of the time elapsed, the third period extending between the second time threshold and a third time threshold occurring after the first time threshold.

Thus, a target operating temperature may be determined for any moment during the usage session. The target operating temperature varies over the duration of the usage session. The target operating temperature may be described as an instantaneous target operating temperature or a dynamic target operating temperature. The target operating temperature depends on both the value of a user interaction parameter, for example number of user puffs taken at that moment during the usage session, and on time that has elapsed from a trigger event, for example time elapsed since the last user puff. By controlling the supply of power to the heater such that the temperature of the heater is maintained at, or as close as possible to, the target operating temperature for the duration of the usage session, the heater, and consequently the aerosol-forming substrate, may be maintained at an optimum temperature for aerosol generation whether a user takes closely spaced puffs or more widely spaced puffs. By associating a monitored user interaction parameter, for example an applied puff, with a corresponding target operating temperature for the heater based on a cumulative value of that user interaction parameter, for example on cumulative puff count, it is possible to adjust the target operating temperature of the heater to take account of the specific puff characteristics of an individual user. This contrasts with known devices and thermal profiles discussed above, in which the temperature of the heater is varied as a function of the time elapsed in a usage session. The ability to adjust the target operating temperature of the heater according to the specific puff characteristics of an individual user may allow for more efficient extraction of aerosol from the aerosol-forming substrate. Efficient aerosol extraction from the substrate may be achieved regardless of (or with less dependence on) the rate at which an individual user applies puffs to the aerosol-generating device. Therefore, a user may be able to extract substantially all aerosol from the substrate without being limited to applying puffs at a predetermined rate. These advantages may also provide the user with an enhanced user experience over the usage session.

A benefit may occur if the change in target operating temperature were only based on the user interaction parameter. For example, if each puff detected during a usage session acted as a trigger event instigating a change in target operating temperature, the thermal profile applied to an aerosol forming substrate over the course of the usage session would be dynamically tailored to the specific use during that usage session. Differences in aerosol delivery may occur, however, depending on whether a user takes a subsequent puff quickly or slowly following a previous puff. For example, if a user puff acts as a trigger event that increases the target operating temperature by 10 degrees Celsius, the quality of the aerosol delivered during a subsequent puff will differ depending on whether the subsequent puff is taken after 5 seconds or 35 seconds. Following an increase in target operating temperature the power supply of the device may be controlled to increase the actual temperature of the heater to the new target operating temperature as swiftly as possible. There is a certain inertia inherent in the heater, but the temperature will swiftly rise to meet the new target operating temperature. Once at the new target operating temperature, it may be a further few seconds before the aerosol-forming substrate is also heated to the new temperature. After about 5 seconds the heater and substrate are likely to have reached a sufficient temperature for any subsequent puff to result in an optimised delivery of aerosol. If the temperature of the heater is maintained at this temperature, a satisfactory delivery is likely to occur should a user take a puff within a window of between, for example 5 seconds and 20 seconds of time elapsed since the trigger event, i.e. the previous puff. If there is long delay between puffs, however, the aerosol-forming substrate may have been maintained at the target operating temperature for too long. Aerosol may begin to deplete and there may be condensation of aerosol within the aerosol generating system. As the time elapsed from the trigger event increases beyond, say, 20 seconds, the quality of aerosol delivered on the subsequent puff may decrease. In order to account for this, the target operating temperature is varied with reference to the time elapsed from the trigger event so that the temperature of the heater, and of the aerosol forming substrate, is preferably maintained at an optimal temperature however much time has elapsed between a previous puff and a subsequent puff.

The method may be described as a method for optimising the heating of an aerosolforming substrate during a usage session, for example a method for applying a dynamic heating profile to the aerosol-forming substrate based on user interaction and passage of time during the usage session.

As used herein, the term “aerosol-generating device” refers to a device that interacts with an aerosol-forming substrate to generate an aerosol. The aerosol-forming substrate may be part of an aerosol-generating article, for example part of a smoking article. An aerosolgenerating device may comprise one or more components used to supply energy from a power supply to an aerosol-forming substrate to generate an aerosol. For example, an aerosolgenerating device may be a heated aerosol-generating device. An aerosol-generating device may be an electrically heated aerosol-generating device or a gas-heated aerosol-generating device. An aerosol-generating device may be a smoking device that interacts with an aerosolforming substrate of an aerosol-generating article to generate an aerosol that is directly inhalable into a user’s lungs through the user's mouth.

As used herein, the term “aerosol-forming substrate” refers to a substrate capable of releasing volatile compounds that can form an aerosol. Such volatile compounds may be released by heating the aerosol-forming substrate. An aerosol-forming substrate may be solid or liquid or comprise both solid and liquid components. An aerosol-forming substrate may be adsorbed, coated, impregnated or otherwise loaded onto a carrier or support. An aerosolforming substrate may conveniently be part of an aerosol-generating article or smoking article.

An aerosol-forming substrate may comprise nicotine. An aerosol-forming substrate may comprise tobacco, for example may comprise a tobacco-containing material containing volatile tobacco flavour compounds, which are released from the aerosol-forming substrate upon heating. In preferred embodiments an aerosol-forming substrate may comprise homogenised tobacco material, for example cast leaf tobacco. An aerosol-forming substrate may comprise at least one aerosol-former, such as propylene glycol or glycerine. As used herein, the term “usage session” refers to a period in which a series of puffs are applied by a user to extract aerosol from an aerosol-forming substrate. A usage session may have a define start point and a defined end point.

As used herein, the term “cumulative puff count” refers to the number of puffs applied by a user in a usage session, relative to the start of that usage session.

The user interaction parameter may be a parameter selected from the list consisting of user puffs, volume of aerosol generated, intensity of user puff, and energy delivered from the power supply to the heater. Preferably, the user interaction parameter is user puffs. Preferably, the aerosol-generating device is configured to monitor and detect user puffs and to record user puffs taken during a usage session. The cumulative value of the user interaction parameter may be, therefore, either a cumulative number of user puffs taken during the usage session, or a cumulative volume of aerosol generated during the usage session, or a cumulative energy delivered from the power supply to the heater during the usage session.

The user interaction parameter may be a combination of parameters. For example, the target operating temperature may be determined with reference to both user puff and intensity of those user puffs, or user puffs and volume of aerosol generated by those puffs. In this manner, the target operating temperature for the heater may, for example, be a function of both i) the cumulative puff count of the applied puff and ii) the intensity of an earlier puff. Puff intensity can affect both depletion of the aerosol-forming substrate and the temperature of the substrate. The greater the intensity of a puff applied by a user, the more aerosol is generated in response to that puff and the more the substrate becomes depleted of those compounds necessary for aerosol formation. Further, a puff of higher than expected intensity may cause cooling of the substrate below a level needed to ensure efficient extraction of aerosol from the substrate. As the substrate becomes more depleted, more energy - and consequently a higher heater temperature - is required to extract the remaining compounds necessary for aerosol formation. So, having the determination of a target operating temperature for the heater being additionally based on an intensity of an earlier puff provides a benefit of enabling the target operating temperature to be adjusted to counter substrate depletion caused by the intensity characteristics of the puffs applied by an individual user. This thereby enables efficient extraction of aerosol from the substrate to be maintained regardless of (or with less dependence) on the intensity of puffs applied by the user. Preferably, the earlier puff immediately precedes the applied puff in the usage session.

The intensity of a given puff can be characterised in various ways. By way of example, the intensity of a puff may be characterised by the volume of aerosol generated from the substrate in response to that puff. Accordingly, the method may further comprise: determining a volume of aerosol generated from the aerosol-forming substrate in response to the earlier puff, and using the determined volume to determine the intensity of the earlier puff.

The usage session may have a usage session start and a usage session end, and the usage session may have a usage session duration extending between the usage session start and the usage session end. Duration of the usage session may be determined with respect to a threshold value of time elapsed from the usages session start, or a threshold value of the user interaction parameter, for example a threshold number of user puffs taken during the usage session. Preferably, duration of the usage session may be determined with respect to both a threshold value of time elapsed from the usages session start, and a threshold value of the user interaction parameter, for example a threshold number of user puffs taken during the usage session. As an example, a usage session may have a maximum duration determined by the first to occur of a time threshold from the start of the usage session and a maximum number of user puffs taken during the usage session.

The trigger event is preferably a user puff. For example, the trigger event may be an immediately previous user puff applied during the usage session. The trigger event may result in a new value of the target operational temperature of the heater. Time elapsed from the trigger event is monitored. The may be one, two, three, four, or more time thresholds associated with a period of time elapsed from the trigger event. Unless a subsequent puff results in a new trigger event, or the end of the usage session, time elapsed from the trigger event may pass through the one, two, three, four, or more time thresholds. The or each or the time thresholds may mark a change in the target operating temperature. The or each or the time thresholds may mark a change in the rate of change of the target operating temperature. A first period of the time elapsed may be that defined between the trigger event and the first time threshold. A second period of the time elapsed may be that defined between the first time threshold and the second time threshold. A third period of the time elapsed may be that defined between the second time threshold and a third time threshold. A fourth period of the time elapsed may be that defined between the third time threshold and the fourth time threshold. More than four periods of time may be defined.

The trigger event may be a detected onset of a user puff, or detected end point of a user puff. The trigger event may be determined to be a predetermined time following a detected onset of a user puff, or a predetermined time following a detected end point of a user puff. Preferably, a subsequent user puff acts as a new trigger event. For example, a detected onset of a subsequent user puff, or detected end point of a subsequent user puff may act as a new trigger event resulting in a new target operating temperature and the start of a new period of time elapsed from a trigger event.

Although a trigger event associated with user puff count may be convenient, there may be other trigger events. For example, the trigger event may be a threshold value in cumulative volume of aerosol generated during the usage session.

The trigger event may be, if no puff has been taken, a detected usage session start. The trigger event may be, if at least one puff has been taken, a user puff or a threshold value in cumulative volume of aerosol.

Thus, a usage session may be started, and the start of the usage session may also be a first trigger event resulting in a first initial value of the target operating temperature being determined. The controller may then control power supplied to the heater such that the temperature moves towards and is maintained at the target operating temperature. Time elapses from the first trigger event and the target operating temperature may vary at a first rate of change. The first rate of change may result in the target operating temperature increasing, decreasing, or remaining the same. If the target operating temperature remains the same, the rate of change during that period of elapsed time is zero. The first rate of change may be linear or non-linear. If a user puff is not taken, the time elapsed from the first trigger event may reach a first time threshold. The time between the first trigger event and the first time threshold is the first period of the time elapsed. The second period of the time elapsed starts at the first time threshold and may extend until a second time threshold. During the second period of time the target operating temperature varies at a second rate of change. The second rate of change is different from the first rate of change. If at any moment after the trigger event the user takes a puff, a second trigger event occurs. For example, the second trigger event may be the end of a detected user puff. On detection of the second trigger event a second initial value of the target operating temperature is determined. The second initial value may be the same as the first initial value of different to the first initial value. After the second trigger event the target operating temperature varies as described above, until a third trigger event is detected. The process repeats on detection of each subsequent trigger event, for example at the detected end point of each user puff until the end of the usage session. Throughout the usage session the target operating temperature is varied, both with regard to the number of user puffs taken and with regard to the length of time elapsed between subsequent user puffs. The power supplied to the heater is controlled to maintain the temperature of the heater as close as possible to the target operating temperature, and the user experience is preferably optimised for each puff. The control electronics preferably include at least one microprocessor and at least one memory. Preferably the control electronics are arranged to monitor and record the user interaction parameter. Preferably the control electronics are arranged to detect the trigger event. Preferably the control electronics are arranged to determine the target operating temperature. Preferably the control electronics are arranged to control the supply of power from the power supply to control the temperature of the heater.

The target operating temperature may periodically, or continuously, redetermined. For example, the target operating temperature may be redetermined which a frequency of between every 0.1 millisecond and every 100 milliseconds, for example between every 0.2 millisecond and every 50 milliseconds, or between every 0.5 millisecond and every 10 milliseconds.

The target operating temperature may vary from the initial value at a third rate of change, different from the second rate of change, during a third period of the time elapsed after the trigger event. The third period extends between the second time threshold and a third time threshold occurring after the second time threshold.

There are many possibilities for the variation in rate of change after a detected trigger event. For example, the target operating temperature may vary linearly or non-linearly during the first period of the time elapsed. The target operating temperature may vary linearly or non- linearly during the second period of the time elapsed. The target operating temperature may vary linearly or non-linearly during a third, or any subsequent, period of the time elapsed.

In some examples, one of the first rate of change or second rate of change is zero. In some examples, at least one of the first rate of change and second rate of change is a positive rate of change. In some examples, at least one of the first rate of change and second rate of change is a negative rate of change. In some examples, at least one of the first rate of change and the second rate of change, and preferably both the first rate of change and the second rate of change is a parabolic rate of change.

There may be a third period of time elapsed after the trigger event. Thus, in some examples one of the first rate of change, or second rate of change, or third rate of change is zero. In some examples, at least one of the first rate of change, second rate of change, and third rate of change is a positive rate of change. In some examples, at least one of the first rate of change , second rate of change, and third rate of change is a negative rate of change. In some examples, at least one of the first rate of change, second rate of change, and the third rate of change, and preferably at least the second rate of change and the third rate of change is a parabolic rate of change. In some examples, the first rate of change is zero and the second rate of change and the third rate of change are negative. The trigger event may be a first trigger event. There may be a plurality of trigger events over the duration of a usages session. In some examples, the first period of the time elapsed from the, or each, trigger event to the first time threshold is between 1 second and 20 seconds, for example between 5 and 15 seconds, for example between 8 and 12 seconds, for example about 10 seconds. The second period of the time elapsed from the first time threshold to the second time threshold may be between 1 second and 20 seconds, for example between 5 and 15 seconds, for example between 8 and 12 seconds, for example about 10 seconds. Where there is a third period of time following the, or each trigger event, the third period of the time elapsed from the second time threshold to the third time threshold may be between 1 second and 40 seconds, for example between 5 seconds and 30 seconds, for example between 10 and 20 seconds. Where there is a fourth period of time following the, or each trigger event, the fourth period of the time elapsed from the third time threshold to the fourth time threshold is between 1 second and 40 seconds, for example between 5 seconds and 30 seconds, for example between 10 and 20 seconds. Where there is a fifth period of time period of time following the, or each trigger event, the fifth period of the time elapsed from the fourth time threshold to the fifth time threshold may be between 1 second and 40 seconds, for example between 5 seconds and 30 seconds, for example between 10 and 20 seconds.

Preferably, at the detection of a subsequent trigger event the target operating temperature is assigned a new initial value. For example, where the trigger event is a first trigger event and the initial value of the target operating temperature is a first initial value, at the detection of a second trigger event occurring after the first trigger event, the instantaneous operating temperature is determined to have a second initial value. In this example, the target operating temperature preferably varies from the second initial value at a first rate of change during a first period of the time elapsed, the first period of time extending between the second trigger event and a first time threshold, and at a second rate of change, different from the first rate of change, during a second period of the time elapsed, the second period extending between the first time threshold and a second time threshold occurring after the first time threshold.

The usage session preferably has a maximum duration determined by a maximum time threshold and a maximum puff threshold. Preferably, the usage session ends when the first of the maximum time threshold of the maximum puff threshold is reached. The usage session may have a maximum number of n allowed puffs. Each puff from puff n=1 to puff n=n-1 may provide a trigger event resetting the initial value of the target operating temperature to a new value. Thus, each of first second, third, and subsequent user puffs taken during the usage session may be associated with corresponding first, second, third, and subsequent initial values of target operating temperature. The aerosol-generating device may store a predetermined thermal profile defining a variation in heater temperature over a predetermined distribution of puffs, wherein initial values of the target operating temperature associated with each applied puff is a temperature of the predetermined thermal profile for the puff in the predetermined distribution of puffs corresponding to the cumulative puff count of the applied puff. The target operating temperature may vary over the usage session within a range of 280 degrees Celsius to 380 degrees Celsius, for example 300 degrees Celsius to 370 degrees Celsius, for example 320 degrees Celsius to 350 degrees Celsius.

In advantageous embodiments, the target operating temperature may vary over the usage session within a range of 320 degrees Celsius to 350 degrees Celsius. Such an operating temperature range has been found especially suitable when generating aerosol from aerosol-forming substrates which are solid and comprise tobacco. However, the present disclosure is not limited to the use of solid aerosol-forming substrates, and may also be applied to use with liquid aerosol-forming substrates. It may be also desirable to limit a maximum value for the target operating temperature over the usage session so as to avoid ignition and combustion of the substrate and the evolution of harmful compounds from the substrate; by way of example, an upper limit on the target operating temperature may be set at 400 degrees Celsius, or 375 degrees Celsius, or 350 degrees Celsius. The specific range and limit for target operating temperature over a usage session may be set according to the heating characteristics of the specific aerosol-forming substrate which is used, as well as the energy capacity of the power source which is used.

Determination of a temperature of the heater may be performed directly by use of a temperature sensor. Preferably however, the temperature of the heater is determined indirectly based upon a change in one or more operating parameters of the aerosol-generating device. For example, the temperature of the heater may be determined based upon an electrical resistance of the heater; this is particularly relevant to where the heater is a resistive heater. In another example, if the heater takes the form of a susceptor which in use is heated by an inductor, the temperature of the susceptor may be determined based upon changes in the current supplied to the inductor from the power supply. The method may require the detection of a user puff. A puff may be detected by means such as an airflow sensor or a thermal sensor to detect airflow associated with a user puff. The method may comprise a step of detecting an applied puff by monitoring a change in heater temperature in response to the applied puff.

The usage session may have a finite duration. The method may further comprise terminating the usage session upon the first to occur of: i) a cumulative number of puffs applied in the usage session reaching a predetermined puff limit, or ii) the usage session reaching a predetermined maximum time duration. A usage session may further be terminated if a fault condition is detected. By way of example, a predetermined puff limit or puff threshold for a usage session may be between 10 puffs and 14 puffs, for example 12 puffs, and a predetermined maximum time duration or threshold may be between 4.5 minutes and 6.5 minutes, for example 6 minutes. However, other values for the puff limit and maximum time duration may be set, with their selection affected by a number of factors. These factors may include the amount and composition of aerosol-forming substrate which is used and the amount of power available from the power supply in a given usage session. It is preferable for the aerosol-generating device to be portable and to have a size and a mass suitable for the device to be held by the hand of a user. These preferences will, in turn, affect the size and energy capacity of the power source of the aerosol-generating device, which will thereby affect the values set for the puff limit and maximum time duration of a usage session.

According to a second aspect of the present invention, there is provided a computer- readable medium for use in an aerosol-generating device, the computer-readable medium containing instructions for performing the method of the first aspect and any of its variants as described above. The computer-readable medium may comprise a computer memory. The computer-readable medium may be provided in a controller used to control the power supply. Alternatively, the computer-readable medium may be a discrete component separate to but accessible to such a controller. Preferably, the computer-readable medium is both readable and writable in use, which thereby provides a benefit of enabling a thermal profile stored in the computer-readable medium to be modified during the course of a usage session. A computer- readable medium for use in an aerosol-generating device, or incorporated within an aerosolgenerating device, may contain instructions for performing the method according to any aspect described herein.

According to a third aspect of the present invention, an aerosol-generating device for generating aerosol from an aerosol-forming substrate during a usage session may be provided. The aerosol-generating device may comprise: a power supply arranged to supply power to a heater to control temperature of the heater during the usage session, and control electronics. The control electronics are preferably configured to: determine a target operating temperature for the heater, the target operating temperature being determined with reference to a) a cumulative value of a user interaction parameter monitored during the usage session, and b) time elapsed from a trigger event; and use the target operating temperature to control temperature of the heater. The target operating temperature may be determined to have an initial value on detection of the trigger event. The target operating temperature may vary from the initial value at a first rate of change during a first period of the time elapsed, the first period of time extending between the trigger event and a first time threshold, and at a second rate of change, different from the first rate of change, during a second period of the time elapsed, the second period extending between the first time threshold and a second time threshold occurring after the first time threshold. The aerosol-generating device may comprise a computer readable medium according to the second aspect of the invention.

The aerosol-generating device may comprise the heater. By way of example, the heater may be a resistive heating element which is intended to fit around or within an aerosol-forming substrate. Alternatively, the heater may be distinct and separate to the device. For example, the heater may be a susceptor forming part of an article distinct from the device, in which the article houses the aerosol-forming substrate. In such an example, the aerosol-generating device may comprise an inductor, with the power supply configured to provide power to the inductor such that, in use of the device with the article, the inductor would induce eddy currents into the susceptor, thereby resulting in heating of the susceptor.

Preferably, the aerosol-generating device is configured to perform a method as set out in any aspect described herein.

According to a fourth aspect of the present invention, an aerosol-generating system may be provided. The system may comprise an aerosol-generating device according to the third aspect of the invention and an aerosol-generating article. The aerosol-generating article preferably comprises the aerosol-forming substrate, and the aerosol-generating device is configured to receive the aerosol-generating article. The aerosol-forming substrate may be any suitable substrate, for example a solid substrate or a liquid substrate. The substrate may have both solid and liquid components.

In some example, the aerosol-generating article comprises both the heater and the aerosol forming substrate.

In some examples, the aerosol-generating article comprises a susceptor. For example, the heater, or a heating element of the heater, may be a susceptor, and the aerosol-generating device may further comprise an inductor, the inductor being controlled by the control electronics to control temperature of the susceptor.

The invention is defined in the claims. However, below there 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 another example, embodiment, or aspect described herein.

Example Exi. A method of operating an aerosol-generating device for generating aerosol from an aerosol-forming substrate during a usage session, the aerosol-generating device comprising: a power supply arranged to supply power to a heater during the usage session, and control electronics; the method comprising steps of using the control electronics to: determine a target operating temperature for the heater during the usage session, the target operating temperature at a particular moment during the usage session being based on both a value of a cumulative user puff parameter and on a time interval from an immediately previous user puff applied during the usage session; and control the supply of power from the power supply during the course of the user session in order to maintain temperature of the heater at the target operating temperature, in which, during a first period of the time interval the target operating temperature varies at a first average variation rate, and during a second period of the time interval, subsequent to the first period of the time interval, the target operating temperature varies at a second average variation rate different to the first average variation rate.

Example Exii. A method of operating an aerosol-generating device for generating aerosol from an aerosol-forming substrate during a usage session, the aerosol-generating device comprising: a power supply arranged to supply power to a heater to control temperature of the heater during the usage session, and control electronics; the method comprising steps of: determining a target operating temperature for the heater, the target operating temperature being determined with reference to a) a cumulative value of a user interaction parameter monitored during the usage session, and b) time elapsed from a trigger event; and using the target operating temperature to control temperature of the heater.

Example Exiii. A method of operating an aerosol-generating device for generating aerosol from an aerosol-forming substrate during a usage session, the aerosol-generating device comprising: a power supply arranged to supply power to a heater to control temperature of the heater during the usage session, and control electronics; the method comprising steps of: determining a target operating temperature for the heater, the target operating temperature being determined with reference to a) a cumulative value of a user interaction parameter monitored during the usage session, and b) time elapsed from a trigger event; and using the target operating temperature to control temperature of the heater, in which, the target operating temperature is determined to have an initial value on detection of the trigger event, and in which the operating temperature varies from the initial value at a first rate of change during a first period of the time elapsed, and at a second rate of change, different from the first rate of change, during a second period of the time elapsed.

Example Ex1. A method of operating an aerosol-generating device for generating aerosol from an aerosol-forming substrate during a usage session, the aerosol-generating device comprising: a power supply arranged to supply power to a heater to control temperature of the heater during the usage session, and control electronics; the method comprising steps of: determining a target operating temperature for the heater, the target operating temperature being determined with reference to a) a cumulative value of a user interaction parameter monitored during the usage session, and b) time elapsed from a trigger event; and using the target operating temperature to control temperature of the heater, in which, the target operating temperature is determined to have an initial value on detection of the trigger event, and in which the operating temperature varies from the initial value at a first rate of change during a first period of the time elapsed, the first period of time extending between the trigger event and a first time threshold, and at a second rate of change, different from the first rate of change, during a second period of the time elapsed, the second period extending between the first time threshold and a second time threshold occurring after the first time threshold.

Example Ex1A. A method according to Exi, Exii, Exiii, or Ex1 in which the target operating temperature can be described as a dynamic target operating temperature or an instantaneous target operating temperature.

Example Ex2. A method according to any preceding example in which the method is a method for optimising the heating of an aerosol-forming substrate during the usage session, for example a method for applying a dynamic heating profile to the aerosol-forming substrate based on user interaction during the usage session.

Example Ex3. A method according to any preceding example in which the user interaction parameter is a parameter selected from the list consisting of user puffs, intensity of user puff, volume of aerosol generated, and energy delivered from the power supply to the heater.

Example 3A. A method according to any preceding example in which the user interaction parameter is a combination of user puff and intensity of user puff or volume of aerosol generated during a user puff. Example Ex4. A method according to Ex3 in which the cumulative value of the user interaction parameter is either a cumulative number of user puffs taken during the usage session, or a cumulative volume of aerosol generated during the usage session, or a cumulative energy delivered from the power supply to the heater during the usage session.

Example Ex5. A method according to any preceding example in which the usage session has a usage session start and a usage session end, and the usage session has a usage session duration extending between the usage session start and the usage session end.

Example Ex6. A method according to any preceding example in which the trigger event is a user puff, for example an immediately previous user puff applied during the usage session.

Example Ex7. A method according to Ex6 in which the trigger event is detected onset of a user puff, or detected end point of a user puff.

Example Ex8. A method according to Ex6 or Ex7 in which a subsequent user puff acts as a new trigger event.

Example Ex9. A method according to any of Exi to Ex5 in which the trigger event is a threshold value in cumulative volume of aerosol generated during the usage session.

Example Ex10. A method according to any preceding example in which the trigger event is, if no puff has been taken, a detected usage session start, and is, if at least one puff has been taken, a user puff or a threshold value in cumulative volume of aerosol.

Example Ex11. A method according to any preceding example in which the control electronics include at least one microprocessor and at least one memory, preferably in which the control electronics are arranged to monitor and record the user interaction parameter, detect the trigger event, determine the target operating temperature, and control the supply of power from the power supply to control the temperature of the heater.

Example Ex12. A method according to any preceding example in which the target operating temperature is periodically, or continuously, redetermined.

Example Ex13. A method according to Ex12 in which the target operating temperature is redetermined which a frequency of between every 0.1 millisecond and every 10 milliseconds.

Example Ex14. A method according to any preceding example in which the operating temperature varies from the initial value at a third rate of change, different from the second rate of change, during a third period of the time elapsed, the third period extending between the second time threshold and a third time threshold occurring after the second time threshold. Example Ex15. A method according to any preceding example in which the operating temperature varies linearly during the first period of the time elapsed.

Example Ex16. A method according to any of Exi to Ex14 in which the operating temperature varies non-linearly during the first period of the time elapsed.

Example Ex17. A method according to any preceding example in which the operating temperature varies linearly during the second period of the time elapsed.

Example Ex18. A method according to any of Exi to Ex16 in which the operating temperature varies non-linearly during the second period of the time elapsed.

Example Ex19. A method according to any preceding example in which the operating temperature varies linearly during a third or subsequent period of the time elapsed.

Example Ex20. A method according to any of Exi to Ex19 in which the operating temperature varies non-linearly during a third or subsequent period of the time elapsed.

Example Ex21. A method according to any preceding example in which one of the first rate of change or second rate of change is zero.

Example Ex22. A method according to any preceding example in which at least one of the first rate of change and second rate of change is a positive rate of change.

Example Ex23. A method according to any preceding example in which at least one of the first rate of change and second rate of change is a negative rate of change.

Example Ex24. A method according to any preceding example in which at least one of the first rate of change and the second rate of change, and preferably both the first rate of change and the second rate of change is a parabolic rate of change.

Example Ex25. A method according to any preceding example when dependent on example Ex14 in which one of the first rate of change or second rate of change or third rate of change is zero.

Example Ex26. A method according to any preceding example when dependent on example Ex14in which at least one of the first rate of change, second rate of change, and third rate of change is a positive rate of change.

Example Ex27. A method according to any preceding example when dependent on example Ex14 in which at least one of the first rate of change , second rate of change, and third rate of change is a negative rate of change. Example Ex28. A method according to any preceding example when dependent on example Ex14 in which at least one of the first rate of change, second rate of change, and the third rate of change, and preferably at least the second rate of change and the third rate of change is a parabolic rate of change.

Example Ex29. A method according to any preceding example when dependent on example Ex14, in which the first rate of change is zero and the second rate of change and the third rate of change are negative.

Example Ex30. A method according to any preceding example, the method being a method of operating an aerosol-generating device for generating aerosol from an aerosol-forming substrate during a usage session, the usage session having a usage session start and a usage session end, the aerosol-generating device comprising: a power supply arranged to supply power to a heater to control temperature of the heater during the usage session, and control electronics including at least one microprocessor and at least one memory, the control electronics configured to detect and record user puffs taken during the usage session, the method comprising steps of: determining a target operating temperature for the heater, the target operating temperature being determined with reference to a) a cumulative value of user puffs detected during the usage session, and b) time elapsed from a trigger event, the trigger event being an immediately preceding user puff; and using the target operating temperature to control temperature of the heater, in which, the operating temperature is determined to have an initial value on detection of the trigger event, and in which the operating temperature varies from the initial value at a first rate of change during a first period of the time elapsed, the first period of time extending between the trigger event and a first time threshold, and at a second rate of change, different from the first rate of change, during a second period of the time elapsed, the second period extending between the first time threshold and a second time threshold occurring after the first time threshold, and optionally at a third rate of change, different from the second rate of change, during a third period of the time elapsed, the third period extending between the second time threshold and a third time threshold occurring after the first time threshold.

Example Ex31. A method according to any preceding example in which the first period of the time elapsed from the trigger event to the first time threshold is between 1 second and 20 seconds, for example between 5 and 15 seconds, for example between 8 and 12 seconds, for example about 10 seconds.

Example Ex32. A method according to any preceding example in which the second period of the time elapsed from the first time threshold to the second time threshold is between 1 second and 20 seconds, for example between 5 and 15 seconds, for example between 8 and 12 seconds, for example about 10 seconds.

Example Ex33. A method according to any preceding example in which the operating temperature varies from the initial value at a third rate of change, different from the second rate of change, during a third period of the time elapsed, the third period extending between the second time threshold and a third time threshold occurring after the second time threshold, and in which the third period of the time elapsed from the second time threshold to the third time threshold is between 1 second and 40 seconds, for example between 5 seconds and 30 seconds, for example between 10 and 20 seconds.

Example Ex34. A method according to any Ex33 in which the operating temperature varies from the initial value at a fourth rate of change, different from the third rate of change, during a fourth period of the time elapsed, the fourth period extending between the third time threshold and a fourth time threshold occurring after the third time threshold, and in which the fourth period of the time elapsed from the third time threshold to the fourth time threshold is between 1 second and 40 seconds, for example between 5 seconds and 30 seconds, for example between 10 and 20 seconds.

Example Ex35. A method according to any Ex34 in which the operating temperature varies from the initial value at a fifth rate of change, different from the fourth rate of change, during a fifth period of the time elapsed, the fifth period extending between the fourth time threshold and a fifth time threshold occurring after the fourth time threshold, and in which the fifth period of the time elapsed from the fourth time threshold to the fifth time threshold is between 1 second and 40 seconds, for example between 5 seconds and 30 seconds, for example between 10 and 20 seconds.

Example Ex36. A method according to any preceding example in which, at the detection of a subsequent trigger event the target operating temperature is assigned a new initial value.

Example Ex37. A method according to any preceding example in which the trigger event is a first trigger event and the initial value of the target operating temperature is a first initial value, in which at the detection of a second trigger event occurring after the first trigger event, the operating temperature is determined to have a second initial value and in which and in which the target operating temperature varies from the second initial value at a first rate of change during a first period of the time elapsed, the first period of time extending between the second trigger event and a first time threshold, and at a second rate of change, different from the first rate of change, during a second period of the time elapsed, the second period extending between the first time threshold and a second time threshold occurring after the first time threshold.

Example Ex38. A method according to any preceding example in which the usage session has a maximum duration determined by a maximum time threshold and a maximum puff threshold, in which the usage session ends when the first of the maximum time threshold of the maximum puff threshold is reached.

Example Ex39. A method according to any preceding example in which the usage session has a maximum number of n allowed puffs, and in which each puff from puff n=1 to puff n=n-1 provides a trigger event resetting the initial value of the target operating temperature to a new value.

Example Ex40. A method according to any preceding example in which each of first second, third, and subsequent user puffs taken during the usage session are associated with corresponding first, second, third, and subsequent initial values of target operating temperature.

Example Ex41 : A method according to Ex39 or Ex40, in which the aerosol-generating device stores a predetermined thermal profile defining a variation in heater temperature over a predetermined distribution of puffs, wherein initial values of the target operating temperature associated with each applied puff is a temperature of the predetermined thermal profile for the puff in the predetermined distribution of puffs corresponding to the cumulative puff count of the applied puff.

Example Ex42: A method according to any preceding example, in which the target operating temperature varies over the usage session within a range of 280 degrees Celsius to 380 degrees Celsius, for example 300 degrees Celsius to 370 degrees Celsius, for example 320 degrees Celsius to 350 degrees Celsius.

Example Ex43: A method according to any preceding example, the method comprising detecting an applied puff by monitoring a change in heater temperature in response to the applied puff.

Ex44: A method according to any preceding example, the method further comprising terminating the usage session upon the first to occur of: i) a cumulative number of puffs applied in the usage session reaching a predetermined puff limit, or ii) the usage session reaching a predetermined maximum time duration. Ex45: A computer-readable medium for use in an aerosol-generating device, the computer- readable medium containing instructions for performing the method according to any one preceding example.

Ex46: An aerosol-generating device for generating aerosol from an aerosol-forming substrate during a usage session, the aerosol-generating device comprising: a power supply arranged to supply power to a heater to control temperature of the heater during the usage session, and control electronics; in which the control electronics are configured to: determine a target operating temperature for the heater, the target operating temperature being determined with reference to a) a cumulative value of a user interaction parameter monitored during the usage session, and b) time elapsed from a trigger event; and use the target operating temperature to control temperature of the heater, in which, the target operating temperature is determined to have an initial value on detection of the trigger event, and in which the operating temperature varies from the initial value at a first rate of change during a first period of the time elapsed, the first period of time extending between the trigger event and a first time threshold, and at a second rate of change, different from the first rate of change, during a second period of the time elapsed, the second period extending between the first time threshold and a second time threshold occurring after the first time threshold.

Ex47. An aerosol-generating device according to Ex46, in which the device is configured to perform a method as set out in any of examples Ex1 to Ex44.

Ex48. An aerosol-generating system, the system comprising the aerosol-generating device according to Ex46 or Ex47 and an aerosol-generating article, the aerosol-generating article comprising the aerosol-forming substrate, wherein the aerosol-generating device is configured to receive the aerosol-generating article.

Ex49. An aerosol-generating system according to Ex48 in which the aerosol-generating article comprises the heater and the aerosol forming substrate.

Ex50. An aerosol-generating system according to Ex48 or Ex49 in which the aerosolgenerating article comprises a susceptor, for example in which the heater is a susceptor, and the aerosol-generating device comprises an inductor, the inductor being controlled by the control electronics to control temperature of the susceptor.

Examples will now be further described with reference to the figures, in which:

Figure 1 illustrates a schematic side view of an aerosol-generating device;

Figure 2 illustrates a schematic upper end view of the aerosol-generating device of figure 1 ; Figure 3 illustrates a schematic cross-sectional side view of the aerosol-generating device of figure 1 and an aerosol-generating article for use with the device;

Figure 4 illustrates a prior art thermal profile used in the operation of known aerosolgenerating devices;

Figure 5 illustrates a variation in target operating temperature of a heater of an aerosolgenerating device resulting from use of the prior art thermal profile of figure 4, in a scenario in which a user applies successive puffs each spaced apart by 15 seconds;

Figure 6 illustrates a variation in target operating temperature of a heater of an aerosolgenerating device resulting from use of the prior art thermal profile of figure 4, in a scenario in which a user applies successive puffs each spaced apart by 11 seconds;

Figure 7 illustrates a method, in which the target operating temperature for the heater is adjusted as a function of puff count;

Figure 8 illustrates a thermal profile, in which the target operating temperature for the heater is defined as a function of puff count;

Figure 9 illustrates how the target operating temperature of the heater is varied when using the thermal profile of figure 8, in a scenario in which a user applies puffs at uniform intervals;

Figure 10 illustrates how the target operating temperature of the heater is varied when using the thermal profile of figure 8, in a scenario in which a user applies puffs at varying (i.e. non- uniform) intervals;

Figure 11 illustrates how a target operating temperature of the heater is varied with respect to both puffs taken and time following a user puff;

Figure 12 illustrates a further example showing how a target operating temperature of the heater is varied with respect to both puffs taken and time following a user puff;

Figure 13 illustrates a further example showing how a target operating temperature of the heater is varied with respect to both puffs taken and time following a user puff;

Figure 14 illustrates a further example showing how a target operating temperature of the heater is varied with respect to both puffs taken and time following a user puff.

An exemplary aerosol-generating device 10 is a hand-held aerosol generating device, and has an elongate shape defined by a housing 20 that is substantially circularly cylindrical in form (see figures 1 , 2 and 3). The aerosol-generating device 10 comprises an open cavity 25 located at a proximal end 21 of the housing 20 for receiving an aerosol-generating article 30 comprising an aerosol-forming substrate 31. The aerosol-generating device 10 has a battery 26, control electronics 27 and a memory module 28 located within the housing 20. The memory module 28 is readable and writable in use. An electrically-operated heater 40 is arranged within the device 10 to heat at least an aerosol-forming substrate portion 31 of an aerosol-generating article 30 when the aerosol-generating article is received in the cavity 25. The memory module 28 stores a thermal profile accessible to the control electronics 27 during use of the device 10. The thermal profile defines how a target operating temperature for the heater 40 varies in a usage session.

The aerosol-generating device is configured to receive a consumable aerosol-generating article 30. The aerosol-generating article 30 is in the form of a cylindrical rod and comprises an aerosol-forming substrate 31 (see figure 3). The aerosol-forming substrate 31 is a solid aerosolforming substrate comprising tobacco. The aerosol-generating article 30 further comprises a mouthpiece such as a filter 32 arranged in coaxial alignment with the aerosol-forming substrate 31 within the cylindrical rod. The aerosol-generating article 30 has a diameter substantially equal to the diameter of the cavity 25 of the device 10 and a length longer than a depth of the cavity 25, such that when the article 30 is received in the cavity 25 of the device 10, the mouthpiece 32 extends out of the cavity 25 and may be drawn on by a user, similarly to a conventional cigarette.

In use, a user inserts the article 30 into the cavity 25 of the aerosol-generating device 10 and turns on the device 10 by pressing a user button 50 (see figure 1) to activate the heater 40 to start a usage session. The heater 40 heats the aerosol-forming substrate 31 of the article 30 such that volatile compounds of the aerosol-forming substrate are released and atomised to form an aerosol. The user draws on the mouthpiece of the article 30 and inhales the aerosol generated from the heated aerosol-forming substrate 31. After activation, the temperature of the heater 40 increases from an ambient temperature to a predetermined temperature for heating the aerosolforming substrate. The predetermined temperature is defined in the thermal profile stored in memory 28. After activation and over the course of the usage session, the control electronics 27 of the device 10 access the thermal profile stored in the memory module 28 so as to control the supply of power from the battery 26 to the heater 40 to adjust the heater temperature in accordance with the thermal profile. The heater 40 continues to heat the aerosol-generating article 30 until an end of the usage session, when the heater is deactivated and cools. In some specific examples the heater 40 may be a resistance heating element. In some specific examples the heater 40 may be a susceptor arranged within a fluctuating magnetic field such that it is heated by induction.

At the end of the usage session, the article 30 is removed from the device 10 for disposal, and the device 10 may be coupled to an external power source for charging of the battery 26 of the device 10.

The aerosol-generating article 30 for use with the device 10 has a finite quantity of aerosolforming substrate 31 and, thus, a usage session needs to have a finite duration to prevent a user trying to produce aerosol when the aerosol-forming substrate has been depleted. A usage session is configured to have a maximum duration determined by a maximum time period from the start of the usage session. A usage session is also configured to have a duration of less than the maximum time period if a user interaction parameter recorded during the usage session reaches a threshold before elapse of the maximum time period. In a specific example the user interaction parameter is representative of a cumulative number of puffs applied to the device by a user over a usage session, with a threshold of 14 puffs defined for the cumulative number of puffs. So, for this specific example, the aerosol-generating device 10 is configured such that each usage session has a maximum duration defined by the first to occur of: i) 6 minutes from activation of the usage session, or ii) a total of 14 puffs being applied in the usage session.

In prior art devices, the thermal profile used to adjust the temperature of the heater 40 is a predetermined temperature profile which varies the target operating temperature for the heater solely as a function of the elapsed time of a usage session. Figure 4 shows such a prior art thermal profile. The prior art thermal profile is based on the behaviour of an idealised or hypothetical user, and defines a temperature profile for the heater 40 which varies a target operating temperature for the heater 40 solely as a function of elapsed time. The prior art thermal profile of figure 4 is constructed on the assumption that a user applies each successive puff to the device 10 at intervals of 30 seconds, resulting in a usage session having a duration of 6 minutes (360 seconds). These hypothetical or idealised puffs are represented by dashed lines in figure 4.

The operation of the device 10 using the prior art thermal profile of figure 4 is now described for three different scenarios:

In a first scenario, a user activates the device 10 by pressing user button 50 to start a usage session with an unused article 30 and then applies a series of 12 successive puffs spaced apart from each other at intervals of 30 seconds. As the user is applying puffs at a rate which conforms to the assumptions made for the thermal profile of figure 4, the battery 26 (under the control of the control electronics 27) would provide power to the heater 40 for a usage session of 6 minutes, corresponding to 12 puffs spaced 30 seconds apart. In essence, the heater 40 would be adjusted in accordance with the thermal profile shown in figure 4. As a result, the aerosol-forming substrate 31 would be substantially depleted of aerosol.

In a second scenario, the user activates the device 10 by pressing user button 50 to start a usage session with an unused article 30. However, in contrast to the first scenario, after taking the first puff at 30 seconds from the start of the usage session, the user applies all subsequent puffs spaced apart from each other at intervals of only 15 seconds. This higher puff rate results in the usage session being terminated early by the device 10 for the reason that the threshold limit of 14 puffs is reached before the elapse of 6 minutes (360 seconds) in the usage session. The effect of the increased puffing rate on heater temperature over the course of this reduced length usage session can be seen in figure 5, with each applied puff represented by a dashed line. In this second scenario, as the thermal profile assumes successive puffs are applied at a time interval of 30 seconds, the effect of a real-life user applying puffs at a faster rate of one puff every 15 seconds is that the heater 40 never attains the temperatures needed in the second half of the usage session to extract all aerosol from the aerosol-forming substrate 31.

In a third scenario, the user activates the device 10 by pressing user button 50 to start a usage session with an unused article. However, in contrast to the second scenario, after taking the first puff at 30 seconds from the start of the usage session, the user then applies all subsequent puffs spaced apart from each other at intervals of only 11 seconds. As shown in figure 6, this higher puff rate results in the usage session being terminated by the device 10 even earlier than for the second scenario. Again, early termination of the usage session occurs for the reason that the threshold limit of 14 puffs is reached before the elapse of 6 minutes (360 seconds) in the usage session. The effect of the further increased puffing rate on heater temperature over the course of this reduced length usage session can be seen in figure 6, with each applied puff represented by a dashed line. As can be understood from figure 6, the consequences of inadequate heating of the aerosol-forming substrate 31 by the heater 40 are even more severe for this third scenario than they were for the second scenario of figure 5.

Figures 5 and 6 can therefore be seen to illustrate the problems of use of a known thermal profile for a heater which varies target operating temperature for the heater 40 solely as a function of elapsed time.

Figure 7 illustrates a method 100 in which a target operating temperature is varied over the course of a user session with respect number of puffs taken. The method 100 is performed by the aerosol-generating device 10 of the present disclosure when a user applies a series of puffs to the aerosol-generating device 10 during a usage session. In step 101 , an applied puff is associated with a corresponding target operating temperature for the heater 40 based on the cumulative puff count of the applied puff in the usage session. In step 102, for the applied puff, the supply of power from the battery 26 is controlled by the control electronics 27 so as to adjust the temperature of the heater 40 to the target operating temperature associated with the applied puff.

Steps 101 , 102 of method 100 are performed for each of puffs applied by the user in the usage session, until termination of the usage session. The method 100 thereby enables the temperature of the heater 40 to be adjusted as a function of the cumulative puff count in a usage session.

The method 100 would be performed by a combination of the control electronics 27 and a thermal profile stored in the memory module 28. In the course of a usage session, the control electronics 27 would access the memory module 28 to read the thermal profile, and then control the supply of power from the power supply 26 in order to adjust the temperature of the heater 40 according to instructions provided in the thermal profile. However, the thermal profile employed by method 100 is different to the prior art thermal profile described above in relation to figures 4 to 6.

Figure 8 illustrates an example of a thermal profile for use in performing the method 100 with aerosol-generating device 10. However, in contrast to the prior art thermal profile described previously, the thermal profile of figure 8 defines an initial target operating temperature for the heater 40 as a function of puff count. So, for the thermal profile of figure 8, each puff of a usage session is associated with a given initial target operating temperature for the heater 40. The thermal profile of figure 8 defines an initial target operating temperature for each puff of a predetermined distribution of 12 puffs. As stated above, the thermal profile is stored inside the memory module 28 of the aerosol-generating device 10. When a user applies each puff of a series of puffs to the device 10, the control electronics 27 access the memory 28 to read the thermal profile. The control electronics 27 then control the supply of power from the battery 26 to the heater 40 to adjust the target operating temperature for the heater in accordance with the thermal profile of figure 8 and the cumulative puff count of each applied puff.

Figures 9 and 10 show two examples of how the initial target operating temperature for the heater 40 is varied with time when using the thermal profile of figure 8 for a usage session in which a succession of puffs are applied by a user to the aerosol-generating device 10. Figure 9 illustrates the temperature variation where the user applies puffs each spaced apart by a uniform interval, in this case of 15 seconds. Figure 10 illustrates the temperature variation where the user applies puffs each spaced apart by a non-uniform time interval. When examining figures 9 and 10, it can be seen that use of the thermal profile of figure 8 results in the initial target operating temperature being adjusted on the basis of the cumulative puff count of the applied puff in the usage session, rather than being adjusted solely as a function of the elapsed time in a usage session. In essence, the target operating temperature for the heater 40 is adjusted by tracking the puff count of the applied puffs with reference to the thermal profile of figure 8 stored in the memory module 28. So, in contrast to the use of the prior art thermal profile of figure 4, the thermal profile of figure 8 enables the target operating temperature to be increased over the second half of a usage session regardless of the rate and timing of the puffs applied by a user.

Although an improvement in the thermal profile results from associating the target operating temperature with puff count rather than time, there are situations in which the user experience may still be less than optimal. For example, if a user takes a long time between successive puffs, the aerosol-forming substrate may start to deplete due to vaporisation of volatile components. Aerosol formed while the substrate is maintained at temperature may also start to condense within the system, for example within an aerosol-generating article. In order to improve this situation, it may be desirable to include a time dependent component in the target operating temperature profile. Such a profile is illustrated in figure 11. Figure 11 illustrates a portion of a temperature-time curve 1101 showing the evolution of a target operating temperature curve over three successive puffs of a usage session. Although the puffs are labelled puff 1 , puff 2, and puff 3, it is clear that they could be any three successive puffs in a usage session. After puff 1 is taken, the target operating temperature shifts to an initial target operating temperature 1110 (Initial TOT Puff 1) in accordance with a predetermined thermal profile, for example the thermal profile illustrated in figure 8. In this case, puff 1 acts as a trigger event and the initial target operating temperature associated with puff 1 is implemented. Following puff 1 , the target operating temperature decreases 1115 at a rate of 0.2 degree Celsius per second. This continues until puff 2 is taken. If puff 2 is taken 30 seconds after puff 1 , the target operating temperature diminishes by 6 degrees Celsius from the initial target operating temperature 1110 associated with puff 1 by the time puff 2 is taken. This reduction in temperature as a function of time elapsed after puff 1 reduces the depletion of the substrate and condensation that may occur if the target operating temperature remained at the initial target operating temperature for the entire period of time between puff 1 being taken and puff 2 being taken.

Puff 2 acts as a new trigger event and the initial target operating temperature associated with puff 2 1120 is implemented. Following puff 2, the target operating temperature decreases at a rate of 0.2 degree Celsius per second. This continues until puff 3 is taken. If puff 3 is taken 10 seconds after puff 2, the target operating temperature diminishes by 2 degrees Celsius from the initial target operating temperature associated with puff 2 1120 by the time puff 3 is taken.

Puff 3 acts as a new trigger event and the initial target operating temperature associated with puff 3 1130 is implemented. The process outlined above is repeated until the usage session ends, for example after a threshold number of puffs is taken or after a threshold time from the start of the usage session is reached.

One potential problem with the thermal profile illustrated in figure 11 is that the target operating temperature may become too low if a user takes a long pause between subsequent puffs. For example, if the initial target operating temperature is reduced at a rate of 0.2 degrees Celsius until a subsequent puff is taken, the target operating temperature will reduce by 10 degrees Celsius if a user takes 50 seconds between successive puffs. Such a drop in operating temperature may reduce the temperature of the aerosol-forming substrate too much to form an adequate aerosol. To help avoid this situation, the device may be configured to vary the target operating temperature from the initial target operating temperature at a first rate of change for a first period of time following a trigger event and at a second rate of change, different to the first rate of change for a second period of time following the first period of time. An example of such a thermal profile is illustrated in figure 12.

As with Figure 11 , Figure 12 illustrates a portion of a temperature-time curve 1201 showing the evolution of a target operating temperature curve over three successive puffs of a usage session. As with the profile of Figure 11 , each of the three puffs taken is associated with its own initial target operating temperature, and the target operating temperature is varied dynamically with time elapsed from each puff until a subsequent puff is taken.

Thus, after puff 1 is taken, the target operating temperature shifts to an initial target operating temperature 1210 (Initial TOT Puff 1) in accordance with a predetermined thermal profile, for example the thermal profile illustrated in figure 8. In this case, puff 1 acts as a trigger event and the initial target operating temperature associated with puff 1 is implemented. Following puff 1 , the target operating temperature decreases 1215 at a rate of 0.2 degree Celsius per second. This continues for a first period of time until a first time threshold 1216 associated with puff 1 is reached. The first time threshold occurs at a predetermined period of time after puff 1 , for example 20 seconds after puff 1 . At a rate of change of 0.2 degrees Celsius per second, the target operating temperature has reduced by 4 degrees Celsius at the first time threshold. The rate at which the target operating temperature varies is now changed such that the target operating temperature decreases 1217 at a rate of 0.1 degrees Celsius per second until a subsequent puff is taken. If puff 2 is taken 30 seconds after puff 1 , the target operating temperature diminishes by 5 degrees Celsius from the initial target operating temperature 1210 associated with puff 1 by the time puff 2 is taken.

Puff 2 acts as a new trigger event and the initial target operating temperature associated with puff 2 1220 is implemented. Following puff 2, the target operating temperature decreases at a rate of 0.2 degree Celsius per second for a first period of time until the time threshold associated with the second puff. If puff 3 is taken 10 seconds after puff 2, the time elapsed from puff 2 never reaches the time threshold (which is set at 20 seconds after puff 2). Thus, the target operating temperature diminishes by 2 degrees Celsius from the initial target operating temperature associated with puff 2 1220 by the time puff 3 is taken.

Puff 3 acts as a new trigger event and the initial target operating temperature associated with puff 3 1230 is implemented. The process outlined above is repeated until the usage session ends, for example after a threshold number of puffs is taken or after a threshold time from the start of the usage session is reached.

One advantage of the thermal profile illustrated in figure 12 is that any deleterious effects on the target operating temperature after a lengthy pause between puffs are ameliorated. For example, if a user takes 50 seconds between successive puffs, the profile of figure 12 (first rate of change 0.2 degrees per second for 20 seconds followed by 0.1 degrees per second until a subsequent puff would only result in a temperature drop of 8 degrees from the initial target operating temperature.

It should be clear that variation from the initial target operating temperature after a puff need not be only a negative variation. Figure 13 illustrates a portion of a temperature-time curve 1301 showing the evolution of a target operating temperature curve over three successive puffs of a usage session. As with the profile of Figure 11 , each of the three puffs taken is associated with its own initial target operating temperature, and the target operating temperature is varied dynamically with time elapsed from each puff until a subsequent puff is taken.

Thus, after puff 1 is taken, the target operating temperature shifts to an initial target operating temperature 1310 (Initial TOT Puff 1) in accordance with a predetermined thermal profile, for example the thermal profile illustrated in figure 8. In this case, puff 1 acts as a trigger event and the initial target operating temperature associated with puff 1 is implemented. Following puff 1 , the target operating temperature varies 1315 at a rate of 0 degree Celsius per second. That is, the target operating temperature does not change over a first period of time until a first time threshold 1316 associated with puff 1 is reached. The first time threshold occurs at a predetermined period of time after puff 1 , for example 20 seconds after puff 1. The rate at which the target operating temperature varies is now changed such that the target operating temperature decreases 1317 at a rate of 0.2 degrees Celsius per second until a subsequent puff is taken. If puff 2 is taken 30 seconds after puff 1 , the target operating temperature diminishes by 2 degrees Celsius from the initial target operating temperature 1310 associated with puff 1 by the time puff 2 is taken.

Puff 2 acts as a new trigger event and the initial target operating temperature associated with puff 2 1320 is implemented. Following puff 2, the target operating temperature decreases at a rate of 0 degree Celsius per second for a first period of time until the time threshold associated with the second puff. If puff 3 is taken 10 seconds after puff 2, the time elapsed from puff 2 never reaches the time threshold (which is set at 20 seconds after puff 2). Thus, the target operating temperature remains at the initial target operating temperature associated with puff 2 1320 by the time puff 3 is taken.

Puff 3 acts as a new trigger event and the initial target operating temperature associated with puff 3 1330 is implemented. The process outlined above is repeated until the usage session ends, for example after a threshold number of puffs is taken or after a threshold time from the start of the usage session is reached.

For simplicity, examples of thermal profiles illustrated in figures 11 , 12, and 13 have involved linear rates of change in the target operating temperature. Non-linear variations of target operating temperature are also envisaged, and one such example is illustrated in Figure 14.

Figure 14 illustrates a portion of a temperature-time curve 1401 showing the evolution of a target operating temperature curve over three successive puffs of a usage session. As with the profile of Figure 11 , each of the three puffs taken is associated with its own initial target operating temperature, and the target operating temperature is varied dynamically with time elapsed from each puff until a subsequent puff is taken. Thus, after puff 1 is taken, the target operating temperature shifts to an initial target operating temperature 1410 (Initial TOT Puff 1) in accordance with a predetermined thermal profile, for example the thermal profile illustrated in figure 8. In this case, puff 1 acts as a trigger event and the initial target operating temperature associated with puff 1 is implemented. Following puff 1 , the target operating temperature decreases 1415 in a non-linear fashion. For example, the target operating temperature may decrease in accordance with a parabolic curve. After a first time threshold 1416 has been reached (for example a time threshold of 20 seconds from the puff) the target operating temperature may has decreased at an average rate of 0.2 degree Celsius per second. At an average rate of change of 0.2 degrees Celsius per second, the target operating temperature has reduced by 4 degrees Celsius at the first time threshold. The rate of change of the target operating temperature continues to diminish after the first time threshold. Thus, the average rate of change in the target operating temperature is different during a period following the first time threshold compared to a period before the first time threshold.

Puff 2 acts as a new trigger event and the initial target operating temperature associated with puff 2 1420 is implemented. Following puff 2, the target operating temperature again decreases along a parabolic curve.

Puff 3 acts as a new trigger event and the initial target operating temperature associated with puff 3 1430 is implemented. The process outlined above is repeated until the usage session ends, for example after a threshold number of puffs is taken or after a threshold time from the start of the usage session is reached.

For simplicity, the examples presented above have only utilised a single change in rate of target operating temperature. It may be convenient for a thermal profile to include more than one variation in operating temperature between successive puffs. For example, a device or system as described above may be operated using a thermal profile in which the following logic is followed.

Detection of a user puff during a usage session acts as a trigger event to set a target operating temperature at an initial value for the target operating temperature associated with that puff. The initial values of target operating temperature may be, for example, as illustrated in figure 8. The power supply of the device is controlled such that actual temperature of the heater of the device matches the target operating temperature as swiftly as possible.

For a first period between detection of the user puff and a first time threshold the target operating temperature does not vary. This could be expressed as the target operating temperature varies from the initial target operating temperature at a rate of zero. The first period may have a length, for example, of 10 seconds and in that 10 seconds the target operating temperature deviates from the initial target operating temperature by zero degrees Celsius.

For a second period extending between the first time threshold and a second time threshold the target operating temperature decreases at a rate of 1 degree Celsius per second. The second period may last for 5 seconds, in which case the target operating temperature decreases by 5 degrees relative to the initial target operating temperature.

For a third period extending between the second time threshold and a third time threshold the target operating temperature decreases at a rate of 0.4 degrees Celsius per second. The third period may last for 10 seconds, in which case the target operating temperature decreases by a further 4 degrees, for a total decrease of 9 degrees relative to the initial target operating temperature.

For a fourth period extending between the third time threshold and a fourth time threshold the target operating temperature decreases at a rate of 0.15 degrees Celsius per second. The fourth period may last for 20 seconds, in which case the target operating temperature decreases by a further 3 degrees, for a total decrease of 12 degrees relative to the initial target operating temperature.

For a fifth period extending between the fourth time threshold and a fifth time threshold the target operating temperature decreases at a rate of 0.1 degrees Celsius per second. The fifth period may last for 20 seconds, in which case the target operating temperature decreases by a further 2 degrees, for a total decrease of 14 degrees relative to the initial target operating temperature.

After a fifth period, further periods may be defined with further different rates of change in the target operating temperature. Alternatively, a lowest stable temperature may be reached at which the target operating temperature remains until the user takes a puff or the usage session is timed out.

For the purpose of the present description and of the appended claims, except where otherwise indicated, all numbers expressing amounts, quantities, percentages, and so forth, are to be understood as being modified in all instances 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 enumerated herein. In this context, therefore, a number “A” is understood as “A” ± 10% of “A”. Within this context, a number “A” may be considered to include numerical values that are within general standard error for the measurement of the property that the number “A” modifies. The number “A”, in some instances as used in the appended claims, may deviate by the percentages enumerated above provided that the amount by which “A” deviates does not materially affect the basic and novel characteristic(s) 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 enumerated herein.

Claims

1. A method of operating an aerosol-generating device for generating aerosol from an aerosolforming substrate during a usage session, the aerosol-generating device comprising: a power supply arranged to supply power to a heater to control temperature of the heater during the usage session, and control electronics; the method comprising steps of: determining a target operating temperature for the heater, the target operating temperature being determined with reference to a) a cumulative value of a user interaction parameter monitored during the usage session, and b) time elapsed from a trigger event; and using the target operating temperature to control temperature of the heater, in which, the target operating temperature is determined to have an initial value on detection of the trigger event, and in which the target operating temperature varies from the initial value at a first rate of change during a first period of the time elapsed, the first period of time extending between the trigger event and a first time threshold, and at a second rate of change, different from the first rate of change, during a second period of the time elapsed, the second period extending between the first time threshold and a second time threshold occurring after the first time threshold.

2. A method according to claim 1 in which the method is a method for optimising the heating of an aerosol-forming substrate during the usage session, for example a method for applying a dynamic heating profile to the aerosol-forming substrate based on user interaction during the usage session.

3. A method according to any preceding claim in which the user interaction parameter is a parameter selected from the list consisting of user puffs, intensity of user puff, volume of aerosol generated, and energy delivered from the power supply to the heater.

4. A method according to claim 3 in which the cumulative value of the user interaction parameter is either a cumulative number of user puffs taken during the usage session, or a cumulative volume of aerosol generated during the usage session, or a cumulative energy delivered from the power supply to the heater during the usage session.

5. A method according to any preceding claim in which the trigger event is a user puff, for example an immediately previous user puff applied during the usage session.

6. A method according to any preceding claim in which the trigger event is detected onset of a user puff, or detected end point of a user puff.

7. A method according to any preceding claim in which a subsequent user puff acts as a new trigger event.

8. A method according to any preceding claim in which the trigger event is, if no puff has been taken, a detected usage session start, and is, if at least one puff has been taken, a user puff or a threshold value in cumulative volume of aerosol.

9. A method according to any preceding claim in which the control electronics include at least one microprocessor and at least one memory, preferably in which the control electronics are arranged to monitor and record the user interaction parameter, detect the trigger event, determine the target operating temperature, and control the supply of power from the power supply to control the temperature of the heater.

10. A method according to any preceding claim in which the target operating temperature is periodically, or continuously, redetermined.

11. A method according to claim 10 in which the target operating temperature is redetermined with a frequency of between every 0.1 millisecond and every 10 milliseconds.

12. A method according to any preceding claim in which the operating temperature varies from the initial value at a third rate of change, different from the second rate of change, during a third period of the time elapsed, the third period extending between the second time threshold and a third time threshold occurring after the second time threshold.

13. A method according to any preceding claim in which the first period of the time elapsed from the trigger event to the first time threshold is between 1 second and 20 seconds, for example between 5 and 15 seconds, for example between 8 and 12 seconds, for example about 10 seconds.

14. A method according to any preceding claim, in which the aerosol-generating device stores a predetermined thermal profile defining a variation in heater temperature over a predetermined distribution of puffs, wherein initial values of the target operating temperature associated with each applied puff is a temperature of the predetermined thermal profile for the puff in the predetermined distribution of puffs corresponding to the cumulative puff count of the applied puff.

15. An aerosol-generating device for generating aerosol from an aerosol-forming substrate during a usage session, the aerosol-generating device comprising: a power supply arranged to supply power to a heater to control temperature of the heater during the usage session, and control electronics; in which the control electronics are configured to: determine a target operating temperature for the heater, the target operating temperature being determined with reference to a) a cumulative value of a user interaction parameter monitored during the usage session, and b) time elapsed from a trigger event; and use the target operating temperature to control temperature of the heater, in which, the target operating temperature is determined to have an initial value on detection of the trigger event, and in which the target operating temperature varies from the initial value at a first rate of change during a first period of the time elapsed, the first period of time extending between the trigger event and a first time threshold, and at a second rate of change, different from the first rate of change, during a second period of the time elapsed, the second period extending between the first time threshold and a second time threshold occurring after the first time threshold.