Temperature Profile for External Heating

Abstract

A method of controlling aerosol generation in an aerosol generating device is provided. The device comprises a heating chamber configured to at least partially receive an aerosol-generating article including an aerosol-forming substrate, a heater comprising at least one heating element configured to externally heat the aerosol-forming substrate, and a power source for providing power to the heating element. The method comprises controlling power provided to the heating element such that during a first period of time, power is provided to increase the temperature of the heating element from an initial temperature to a first temperature, during a second period of time, power is provided to decrease the temperature of the heating element to a second temperature below the first temperature, and during a third period of time, power is provided to increase the temperature of the heating element to a third temperature higher than the second temperature. The first temperature is a temperature between 230°C and 270°C.

Description

[Technical field]

[0001] The present disclosure relates to a method for controlling aerosol generation in an aerosol generating device, an aerosol generating device for generating an aerosol from an aerosol-forming substrate, and an aerosol generating system comprising an aerosol generating device. [Background technology]

[0002] Aerosol generating devices configured to generate an aerosol from an aerosol-forming substrate, such as a tobacco-containing substrate, are known in the art. Many known aerosol generating devices generate an aerosol by application of heat to the substrate by a heater assembly. The heater assembly is heated when power is provided by a power source of the aerosol generating device. The generated aerosol can then be inhaled by a user of the device.

[0003] Typically, the power source of the aerosol generating device is a portable power source, such as a rechargeable battery, such that the aerosol generating device itself is portable and does not need to be connected to mains power. A disadvantage of portable power sources, such as rechargeable batteries, is that their maximum voltage (and thus maximum power output) often varies depending on the state of charge of the power source. In particular, the maximum voltage that can be supplied by a portable power source is highest when the power source is fully charged and decreases as the portable power source is depleted. This can result in an inconsistent user experience when the power source is fully charged compared to when the power is somewhat or completely depleted.

[0004] The highest power demand during a use session of an aerosol generating device is typically during the initial or pre-heating phase of a puff. This is because during the pre-heating phase, the heater assembly must increase in temperature from an initial temperature, often close to ambient or room temperature, to an operating temperature at which substantial aerosol is generated. It is therefore the pre-heating phase of a use session that is most affected by fluctuations in the voltage of the power supply. In particular, as the power supply becomes depleted, it will take the heater assembly longer to reach operating temperature. A depleted power supply may also reduce the amount of aerosol generated during a use session.

[0005] It is desirable to provide an aerosol generating device that provides a consistent user experience regardless of the state of charge of the power source, and in particular, to provide an aerosol generating device in which the time it takes for the heater assembly to reach an operating temperature is consistent regardless of the state of charge of the power source, and in which the amount of aerosol generated during a usage session is consistent regardless of the state of charge of the power source.

[0006] Aerosol generating devices are often configured to control the heating of the heater assembly according to a predetermined heating routine or profile, which typically includes the pre-heat stage described above, during which high power is supplied to the heater assembly for a period of time to ensure that the heater assembly reaches an operating temperature.

[0007] Where appropriate, it may be desirable to minimize the duration of the pre-heat phase, which would have the advantage of reducing power consumption during a use session, lengthening the time between charges of a portable power source, and reducing the amount of time a user must wait from the start of a use session until the aerosol generating device has produced substantial aerosol.

[0008] Some prior art devices comprise a heater assembly in the form of a heater blade comprising a resistive heater element. These devices are configured to be used with an aerosol-generating article in the shape of a rod and comprise an aerosol-forming substrate at the distal end of the rod. In use, the article is inserted into a cavity of the aerosol-generating device and the heater blade is configured to penetrate the aerosol-forming substrate. Such devices heat the aerosol-forming substrate internally. These devices have the advantage that the substrate and the heater are in direct contact. However, if an external heater assembly is used, the complexity and cost of the aerosol-generating device can be reduced and robustness is improved. In particular, providing a flexible heater assembly having a heater track deposited on a flexible substrate wrapped around the outer surface of the cavity for receiving the aerosol-forming substrate simplifies manufacturing and improves robustness of the aerosol-generating device.

[0009] Both the problem of unstable power and the need to reduce the length of the preheating stage are more severe for devices that employ low-cost heater assemblies that are external to the aerosol-forming substrate. The heater tracks of external heaters typically have a higher resistance than the heater elements of the heater blades. This means that a higher voltage is required for the same amount of heating, which becomes even more pronounced when the battery is depleted. Furthermore, the preheating stage may be longer with external heaters, given that there is no direct contact between the heater elements of the external heater and the aerosol-forming substrate.

[0010] It would be desirable to provide a simple, low-cost aerosol generating device with an external heater assembly that does not suffer from unstable power problems and where necessary, minimizes the duration of the preheating phase.

[0011] As mentioned above, aerosol generating devices often implement some kind of heating routine. To follow a heating routine, the aerosol generating device typically includes means for measuring the temperature of the heater assembly, and operates in response to those temperature measurements, e.g., to heat to a target temperature.

[0012] In some prior art aerosol generating devices, the resistance of the heater element of the heater assembly is highly dependent on temperature, such that the controller of the aerosol generating device can determine the temperature based on the resistance of the heater element.

[0013] An alternative solution is for the aerosol generating device to be equipped with a dedicated temperature sensor to measure the temperature of the heater element. However, the temperature measured by the temperature sensor often does not accurately reflect the actual temperature of the heater element, especially when the temperature of the heater element is changing rapidly. This is because it takes time for the heat from the heater element to be absorbed by the temperature sensor, even if there is direct contact between the temperature sensor and the heater element. This is particularly problematic for low-cost external heaters of the type mentioned above, since it can lead to, for example, the temperature of the heater element overshooting the target temperature, and such heaters can be damaged by the high temperatures associated with overshooting the target temperature.

[0014] It is desirable to provide a low cost heater assembly in which overheating is avoided.

[0015] It is desirable for an aerosol generating device to be able to produce a consistent aerosol over time. In devices where a depletable substrate is heated continuously or repeatedly over time, this can be difficult because the attributes of the aerosol-forming substrate can change significantly with continuous or repeated heating, both in relation to the amount and distribution of aerosol-forming components remaining in the substrate, and in relation to the temperature of the substrate. In particular, users of continuously or repeatedly heated devices may experience a decrease in the flavor, taste, and feel of the aerosol as the substrate is depleted of nicotine and, in certain cases, flavor-carrying aerosol formers. Thus, a consistent aerosol delivery is provided over an extended period of time, such that the aerosol delivered initially is substantially equivalent to the aerosol delivered ultimately during operation. Summary of the Invention

[0016] In a first aspect, a method for controlling aerosol generation in an aerosol generating device is provided. The device comprises a heating chamber configured to at least partially receive an aerosol-generating article including an aerosol-forming substrate, a heater comprising at least one heating element configured to externally heat the aerosol-forming substrate, and a power source for providing power to the heating element. The method comprises controlling power provided to the heating element such that power is provided such that in a first period of time the temperature of the heating element rises from an initial temperature to a first temperature. In a second period of time, power is provided such that the temperature of the heating element falls to a second temperature less than the first temperature. In a third period of time, power is provided such that the temperature of the heating element rises to a third temperature greater than the second temperature. The first temperature is preferably a temperature between 230°C and 270°C. It should be noted that the unit of temperature "°C" is the same as the unit of Celsius or centigrade. Hence, the first temperature can be rephrased as being between 230°C and 270°C.

[0017] The aerosol generating device is preferably configured to continuously or repeatedly heat the aerosol-forming substrate for an extended period of time. This is in contrast to devices in which heating is applied only when the user takes a puff. For example, the device may be configured for continuous heating over the duration of a use session, the use session having a duration of at least 1 minute, preferably at least 2 minutes, such as more than 3 minutes, or more than 4 minutes. The use session preferably has a duration of between 3 and 6 minutes, such as about 4 and a half minutes. The device may be configured for continuous heating over a sequence of several user puffs. For example, the heater may be controlled to heat the aerosol-forming substrate over a sequence of at least 3 user puffs, such as at least 4 user puffs, or at least 6 user puffs. The use session may have a duration that is at least partially controlled by the user puffs. The use session may range in duration from 6 to 16 user puffs, such as from 8 to 14 user puffs, such as from 10 to 12 user puffs.

[0018] As used herein, continuous or repeated heating means that the substrate or a portion of the substrate is heated to generate aerosol for a sustained period, typically greater than 5 seconds, and may extend for example to greater than 30 seconds for the duration of a usage session. In the context of an aerosol generating device, or other device in which a user puffs and draws aerosol from the device, this means heating the substrate for a period that includes multiple user puffs, such that aerosol is continuously generated regardless of whether the user is puffing on the device. In this context, substrate exhaustion can be a significant problem. This is in contrast to flash heating, in which a separate substrate or portion of the substrate is heated for each puff by the user, and no portion of the substrate is heated more than once when the puff duration is about 2-3 seconds long.

[0019] As used herein, the terms "puff" and "inhalation" are used interchangeably and are intended to mean the action of a user drawing an aerosol into their body through their mouth or nose. Inhalation includes situations in which the aerosol is drawn into the user's lungs, as well as situations in which the aerosol is drawn only into the user's mouth or nasal passages before being expelled from the user's body.

[0020] The first, second and third temperatures are preferably selected such that aerosol is generated continuously during the first, second and third time periods. The method includes heating to a first temperature between 230°C and 270°C before lowering the temperature to a second temperature lower than the first temperature. If the heating element is a heater for insertion into the aerosol generating device, it would not be expected that such low temperatures would be able to generate a consistent aerosol over a series of user puffs. However, the use of a low first temperature followed by an even lower second temperature in combination with a heating element configured for external heating of the aerosol generating device appears to allow consistent and complete aerosol generation from the aerosol-forming substrate. This temperature range appears to provide optimal conditions for aerosol generation from an aerosol-generating article including an aerosol-forming substrate when heated within a heating chamber of an aerosol generating device utilizing an external heater, i.e. a heater that provides heat to an external portion of the aerosol-generating article.

[0021] As used herein, "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. The aerosol-generating device may be a smoking device that interacts with the aerosol-forming substrate of the aerosol-generating article to generate an aerosol that can be inhaled directly through the user's mouth into the user's lungs. The aerosol-generating device may be a holder.

[0022] The term "aerosol-forming substrate" as used herein refers to a substrate capable of releasing volatile compounds capable of forming an aerosol. Such volatile compounds may be released by heating the aerosol-forming substrate. The aerosol-forming substrate may conveniently be part of an aerosol-generating article or a smoking article.

[0023] The term "aerosol-generating article" as used herein refers to an article that includes an aerosol-forming substrate that has the ability to emit a volatile compound that can form an aerosol. For example, the aerosol-generating article may be an article that generates an aerosol that can be inhaled directly into the lungs of a user through the mouth of the user. The aerosol-generating article may be disposable.

[0024] The first temperature may be a temperature between 245° C. and 265° C., for example the first temperature may be between 250° C. and 260° C., for example about 255° C. The first temperature may be towards the lower end of the range between 230° C. and 270° C., for example the first temperature may be a temperature between 230° C. and 250° C., for example the first temperature may be between 235° C. and 245° C., for example about 240° C.

[0025] The second temperature may be a temperature between 140° C. and 220° C. For example, the second temperature may be a temperature between 180° C. and 210° C. The second temperature may be a temperature between 190° C. and 200° C., for example, about 195° C. or about 200° C.

[0026] The third temperature may be a temperature between 230° C. and 270° C. The third temperature may be a temperature between 245° C. and 265° C. The third temperature may be a temperature between 250° C. and 260° C., for example, about 250° C. or about 255° C.

[0027] During the first period, the temperature of the heating element is raised to a first temperature at which an aerosol is generated from the aerosol-forming substrate. It is desirable to generate an aerosol having the desired composition as soon as possible after activation of the device. For a satisfactory consumer experience, the "time to first puff" is considered to be very important. A consumer does not want to wait a long time after activation of the device before taking his first puff. For this reason, power may be provided to the heating element during the first period to raise it to the first temperature as quickly as possible. The delivery of the aerosol may be reduced by condensation within the device during the first period of device operation. The first period preferably has a duration of between 20 seconds and 40 seconds, such as between 25 seconds and 35 seconds, for example about 30 seconds.

[0028] Once the first period has ended, a second period begins, during which power to the heating element is controlled to ramp down the temperature of the heating element to a second temperature less than the first temperature. This ramp down of the heating element temperature is desirable because it reduces condensation as the device and substrate warms, thereby increasing aerosol delivery for a given heating element temperature. Additionally, ramping down the heating element temperature reduces the amount of energy consumed by the aerosol generating device. Additionally, varying the temperature of the heating element during operation of the device allows for the introduction of a timed thermal gradient into the substrate. The second period may have a duration of 40 seconds to 100 seconds, such as 50 seconds to 90 seconds, such as 60 seconds to 80 seconds, such as about 70 seconds.

[0029] In the third period, the temperature of the heating element is increased. As the substrate becomes increasingly depleted during the third period, it may be desirable to continuously increase the temperature. The increase in temperature of the heating element during the third period compensates for the reduction in aerosol delivery due to substrate depletion and reduced thermal diffusion. However, the increase in temperature of the heating element during the third period may have any desired temporal profile and may depend on the geometry of the device and substrate, the substrate composition, and the duration of the first and second periods. It is preferred that the temperature of the heating element remains within an acceptable range throughout the third period. In one embodiment, the step of controlling the power to the heating element is performed to continuously increase the temperature of the heating element during the third period. The third period may have a duration of 40 seconds to 100 seconds, such as 50 seconds to 90 seconds, such as 60 seconds to 80 seconds, such as about 70 seconds.

[0030] The aerosol generating device may be configured to generate the aerosol during a use session, the use session having a use session start and a use session end. Preferably, the temperature of the heating element is at the initial temperature at the use session start and the end of the third period is the use session end.

[0031] Controlling the power provided to the heating element may be performed to maintain the temperature of the heating element within a desired temperature range during the second and third time periods of the use session. The desired temperature range may have a lower limit of 140°C to 220°C and an upper limit of 230°C to 270°C.

[0032] The step of controlling the power to the heating element may include measuring the temperature of the heating element or the temperature proximate to the heating element to provide a measured temperature, performing a comparison between the measured temperature and a target temperature, and adjusting the power provided to the heating element based on the results of the comparison. The target temperature preferably varies over time after activation of the device to provide the first, second and third time periods. For example, during the first time period, the target temperature may be a first target temperature, during the second time period, the target temperature may be a second target temperature, and during the third time period, the target temperature may be a third target temperature, with the third target temperature increasing progressively over time. It will be apparent that the target temperature may be selected to have any desired temporal profile within the constraints of the first, second and third phases of operation.

[0033] The first time period may end when the heating element reaches a first temperature. The duration of the second time period may be determined based on a total amount of power provided to the heating element during the second time period.

[0034] The method may include detecting a user puff on the aerosol generating device. The first, second or third time period may end after detecting a predetermined number of user puffs.

[0035] The method may include identifying a characteristic of the aerosol-forming substrate. Controlling the power may be responsive to the identified characteristic.

[0036] The heating element is for externally heating the aerosol-forming substrate. The heating element may be disposed so as to substantially surround the aerosol-generating article received in the heating chamber. The heating element may be disposed around the heating chamber.

[0037] The aerosol generating device may be configured to generate an aerosol during a use session, the use session may include a number of successive stages between a use session start and a use session end, each of the stages of the number of successive stages beginning at a stage start time and ending at a stage end time.

[0038] Preferably, the progression of the use session through the plurality of successive stages is controlled by a controller. The progression of the use session through the plurality of successive stages may be controlled by the controller determining at least one of: a length of time from start of a stage is equal to or greater than a predetermined duration; and a temperature is equal to or greater than a target temperature. During each stage, the controller may be configured to control the supply of power to the heating element such that the heating element is heated with reference to the target temperature.

[0039] The plurality of successive stages may include a first stage having a first stage target temperature. The end of the first stage may be a first predetermined time after the start of the first stage.

[0040] The plurality of successive stages may include a second stage having a second stage target temperature. The second stage may end when the controller determines that the temperature of the heater element is equal to or greater than the second target temperature or when the controller determines that the time elapsed since the second stage began is equal to or greater than a second predetermined time, whichever occurs first.

[0041] The plurality of successive stages may include a third stage having a third stage target temperature. The controller may be configured to repeatedly determine the temperature of the heater element to determine a rate of change of the temperature of the heater element.

[0042] Each of the first period, the second period, and the third period may include multiple successive stages, for example, 1 to 4 successive stages.

[0043] The first period may include a first stage having a first target temperature and a second stage having a second target temperature higher than the first target temperature. The second target temperature may be the same as the first temperature. The first target temperature may be between 200°C and 220°C, for example about 210°C.

[0044] The first stage may end 5-10 seconds after the use session begins, for example, about 8 seconds after the use session begins, and the second stage may end 15-25 seconds after the use session begins, for example, about 20 seconds after the use session begins.

[0045] The first period may further include a third phase having a third target temperature, which may be the same as the first temperature, and the third phase may end 25-35 seconds after the start of the use session, for example, about 30 seconds after the start of the use session.

[0046] The use session may further include a fourth phase having a fourth target temperature, which may be the same as the second temperature, for example, the fourth phase may end 60-90 seconds after the use session begins, for example about 65 seconds after the use session begins.

[0047] The use session may further include a fifth phase having a fifth target temperature. The fifth target temperature may be the same as the second temperature. The fifth phase may end 90-110 seconds after the use session begins, for example, about 105 seconds after the use session begins.

[0048] The second period may include a fourth stage and a fifth stage.

[0049] The use session may further include a sixth phase having a sixth target temperature. The sixth target temperature may be higher than the second temperature. The sixth target temperature may be between 215° C. and 220° C. The sixth phase may end between 150 and 180 seconds after the use session begins, for example, about 165 seconds after the use session begins.

[0050] The use session may further include a seventh phase having a seventh target temperature. The seventh target temperature may be higher than the second temperature, for example, the seventh target temperature may be between 220° C. and 230° C. The seventh phase may end between 180 and 220 seconds after the use session begins, for example, about 200 seconds after the use session begins.

[0051] The use session may further include an eighth phase having an eighth target temperature. The eighth target temperature may be higher than the second temperature, for example, the eighth target temperature may be between 245° C. and 255° C. The eighth phase may end between 230 and 260 seconds after the use session begins, for example, about 250 seconds after the use session begins.

[0052] The use session may further include a ninth stage having a ninth target temperature. The ninth target temperature may be the same as the third temperature, for example, the ninth stage may end between 220 and 280 seconds after the use session begins, for example about 265 seconds after the use session begins.

[0053] The third period may include a sixth, seventh, eighth, and ninth stage.

[0054] In a fourth aspect, an electrically operated aerosol generating device is provided. The device comprises a heating chamber configured to at least partially receive an aerosol-generating article including an aerosol-forming substrate, a heater comprising at least one heating element configured to externally heat the aerosol-forming substrate, a power source for supplying power to the heating element, and an electrical circuit for controlling the supply of power from the power source to the at least one heating element. The electrical circuit is arranged to control the power provided to the heating element such that during a first period of time, power is provided to increase the temperature of the heating element from an initial temperature to a first temperature, during a second period of time, power is provided to decrease the temperature of the heating element to a second temperature below the first temperature, and during a third period of time, power is provided to increase the temperature of the heating element to a third temperature higher than the second temperature. The first temperature is preferably a temperature between 230°C and 270°C.

[0055] The electrical circuit may be configured such that at least one of the first period, the second period, and the third period has a fixed duration.

[0056] The device may further comprise means for detecting a user puff at the aerosol generating device, and the electrical circuit may be configured such that at least one of the first, second or third time periods terminate after detection of a predetermined number of user puffs.

[0057] An electrically operated aerosol generating device may be provided, the device being configured to operate any of the methods disclosed herein.

[0058] In a further aspect, there is provided an aerosol generation system comprising an aerosol generating device as disclosed herein and an aerosol-generating article configured to be received within a heated chamber of the aerosol generating device.

[0059] The aerosol-generating article comprises an aerosol-forming substrate, preferably having a length of at least 5 millimetres, preferably the aerosol-generating substrate has a length of 80 millimetres or less. The aerosol-generating substrate may have a density of 0.5 grams per cubic centimetre or less.

[0060] The aerosol-generating article may have a length of at least 35 millimeters.The aerosol-generating article may have a length of up to 100 millimeters.

[0061] Further suitable aerosol-generating articles are disclosed below.

[0062] In a further aspect, an aerosol generating device for generating an aerosol from an aerosol-forming substrate is provided. The aerosol generating device may be configured to generate an aerosol during a use session. The aerosol generating device may comprise a timer. The aerosol generating device may comprise a heater assembly. The heater assembly may comprise a heater element for heating the aerosol-forming substrate. The aerosol generating device may comprise a power source. The power source may be configured to provide power to the heater assembly. The aerosol generating device may comprise a controller.

[0063] At least a portion of the usage session may be divided into n consecutive time intervals.

[0064] The controller may be configured to limit the power supplied to the heater element during any or each of n consecutive time intervals.

[0065] The power may be limited to a threshold average power. For example, the average power delivered during any or each successive interval may not exceed the threshold for that time interval. That is, any or each of n successive time intervals may have an average power threshold, and the average of the power delivered during the time interval may not exceed the respective threshold average power. The threshold average power may be different for each time interval. Preferably, the threshold average power may be the same for each time interval.

[0066] As an example, during a portion of the or each time interval, the instantaneous power supplied to the heater assembly may be higher than the threshold average power for that time interval. To account for this, the instantaneous power supplied to the heater assembly for another portion of the time interval may be lower than the threshold average power for that time interval. In this manner, the average power supplied during any or each time interval may be limited so as not to exceed the respective threshold average power. Preferably, the instantaneous power supplied to the heater assembly during a time interval may be higher than the threshold average power for that time interval or may be zero.

[0067] As used herein, "instantaneous power" means the power supplied to a heater assembly measured at a given moment. The instantaneous power may be higher than a threshold average power. Additionally or alternatively, the instantaneous power may be lower than a threshold average power. When the instantaneous power is lower than the threshold average power, the instantaneous power may preferably be zero.

[0068] In a particular example, the threshold average power supplied to the heater assembly during the time interval may be 10.8 watts. For a first portion of the time interval (e.g., the first half of the time interval), an instantaneous power of 21.6 watts, which is higher than the threshold average power, may be supplied. For a second portion of the time interval (e.g., the second half of the time interval), the instantaneous power supplied to the heater assembly may be zero. In this manner, the average power supplied to the heater assembly during the time interval may be 10.8 watts. In other words, the power, particularly the average power, supplied during the time interval may be limited to the threshold average power. In another example, the threshold average power for the time interval may be 10.8 watts. An instantaneous power of 14.4 watts may be supplied to the heater assembly during three-quarters of the time interval. The power supplied during the remaining quarter of the time interval may be zero to ensure that the average power during that time interval does not exceed 10.8 watts.

[0069] The controller may be configured to limit the power supplied to the heater assembly during any or each of n consecutive time intervals so as not to exceed a threshold energy for that time interval. Preferably, the threshold energy is not exceeded for each of the n consecutive time intervals.

[0070] The threshold energy may correspond to a maximum amount of energy supplied to the heater assembly during each time interval. Because of the relationship between power and energy, limiting the power supplied during any or each of n consecutive time intervals to a threshold average power may be rephrased as limiting the power supplied during any or each of n consecutive time intervals to not exceed the threshold energy for that interval.

[0071] The threshold energy may be equal to the power threshold multiplied by the length of the time interval. This may be because energy is equal to power multiplied by time. The threshold energy may be different for different time intervals. For example, the threshold energy may be different for different time intervals if the lengths of n consecutive time intervals are different. Alternatively or additionally, the threshold energy may be different for different time intervals if the threshold average power is different for different time intervals.

[0072] Limiting the power or energy supplied to the heater assembly during any or each of n consecutive time intervals may advantageously reduce or minimize inconsistencies in the amount of power or energy supplied by the power source during n consecutive time intervals in different use sessions.

[0073] As used herein, a "use session" refers to a period of use of a device beginning with activation of the device by a user. A use session may include a pre-heating phase in which the aerosol generating device is configured to supply power to the heater assembly to heat the aerosol-forming substrate to generate an aerosol. A use session may include a main phase in which the user may inhale the generated aerosol. The main phase may be long enough for multiple puffs. The main phase may be long enough for three, four, five, or six puffs. The main phase may be long enough for seven or more puffs. At the end of the use phase, the aerosol generating device may be configured to stop supplying power to the heater assembly. The aerosol-forming substrate may be removed from the aerosol generating device at the end of the use session. The aerosol-forming substrate may be replaced in a subsequent use session. The duration of the use session between the start of the use session and the end of the use session may be at least 1 minute, 2 minutes, 3 minutes, 4 minutes, 5 minutes, or 6 minutes. Preferably, the use session may have a duration of about four and a half minutes.

[0074] The inconsistency in the energy or power provided by the power source in different usage sessions can be a particular problem when the power source is a portable source for storing energy. The portable source can be a battery, for example a rechargeable battery.

[0075] Each subsequent use session may loosen the energy of such a portable power source, and therefore make it more depleted. As the portable power source becomes depleted, the maximum voltage that can be supplied may decrease, and therefore the maximum instantaneous power that can be supplied by the portable power source may decrease. Since energy is related to power, the maximum energy that the power source can supply to the heater assembly in a given period of time may also decrease as the maximum instantaneous power decreases. Thus, without any kind of limitation on the power or energy supplied, the maximum instantaneous power supplied during an early use session when the portable power source is fully charged may be higher compared to later use sessions when the portable power source is depleted.

[0076] Limiting the power supplied during any or each of n consecutive time intervals may advantageously mean that consistent power can be supplied during any or each time interval, regardless of the state of charge of the power source.

[0077] Energy is related to power in that it is equal to the power delivered multiplied by the time. Thus, limiting the power delivered during a time interval also limits the energy delivered to the heater assembly during that time interval. Limiting the power to not exceed a threshold energy for n consecutive time intervals may advantageously mean that a consistent amount of energy is delivered during any or each of the n consecutive intervals, regardless of the state of charge of the power source. This may be because the threshold energy for the nth consecutive interval corresponds to the maximum amount of energy that the power source can deliver to the heater assembly during any or each of the n consecutive time intervals at most states of charge of the power source. Given the relationship between power and energy, the threshold energy may depend on the length of the nth consecutive time interval.

[0078] The threshold energy may relate to an amount of energy supplied to the heater assembly during any or each of n consecutive time intervals, preferably any or each of n consecutive time intervals. The threshold energy may be less than 1 Joule supplied to the heater assembly during any or each of n consecutive time intervals. Preferably, the threshold energy is less than 0.8 Joule supplied to the heater assembly during any or each of n consecutive time intervals. Even more preferably, the threshold energy is less than 0.6 Joule supplied to the heater assembly during any or each of n consecutive time intervals. These amounts of threshold energy advantageously represent the amount that the portable power source is capable of supplying, even after multiple usage sessions.

[0079] The threshold energy may be greater than 0.4 Joules. Preferably, the threshold energy may be greater than 0.45 Joules. Even more preferably, the threshold energy may be greater than 0.5 Joules. It is advantageous to limit the amount of energy delivered during any or each of the n time intervals, but it is important not to limit the energy too much or there will not be enough energy available to adequately heat the heater assembly to a temperature at which a substantial aerosol is generated.

[0080] The threshold energy may be less than the maximum energy that can be delivered by the power source in any or each of the n consecutive time intervals when the power source is fully charged. The threshold energy may advantageously be selected as the amount of energy that the portable power source can provide in any or each of the n consecutive time intervals, even after at least 5, at least 10, at least 15, or even at least 20 usage sessions. For example, the threshold energy may be at least 10% lower than the maximum energy. Preferably, the threshold energy may be at least 15% lower than the maximum energy. Even more preferably, the threshold energy may be at least 20% lower than the maximum energy.

[0081] Of course, the length of the time intervals may also be important to account for the above energy values ​​supplied to the heater assembly. The above energy values ​​are particularly preferred and advantageous when any or each of the n consecutive time intervals is equal to 10 seconds or less, preferably 1 second or less, preferably 500 milliseconds or less, even more preferably 100 or less, even more preferably 75 milliseconds or less, and most preferably about 50 milliseconds.

[0082] Considering the relationship between power and energy, limiting the power supplied to a heater assembly during any or each of n consecutive time intervals so as not to exceed a threshold energy from the n consecutive time intervals may alternatively or additionally be described as limiting the power so that the power supplied throughout any or each of n consecutive time intervals does not exceed a threshold average power.

[0083] The threshold power may be less than the maximum power that can be delivered by the power source. The threshold average power may be less than the maximum power that can be delivered during any or each of the n consecutive time intervals when the power source is fully charged. The threshold average power may advantageously be selected as the amount of power that the portable power source can provide during any or each of the n consecutive time intervals, even after at least 5, at least 10, at least 15, or even at least 20 usage sessions. For example, the threshold average power may be at least 10% lower than the maximum power. Preferably, the threshold average power may be at least 15% lower than the maximum power. Even more preferably, the threshold average power may be at least 20% lower than the maximum power.

[0084] The threshold average power may be less than 13 Watts, preferably less than 12 Watts, and even more preferably less than 11 Watts. The threshold average power may be greater than 8 Watts, preferably greater than 9 Watts, and even more preferably greater than 10 Watts.

[0085] The controller limiting the power or energy supplied to the heater assembly during any or each of n consecutive time intervals may include the controller being configured to monitor a cumulative amount of energy supplied to the heater assembly from a beginning of the nth time interval. The controller may be further configured to limit the supply of power or energy to the heater assembly until an end of the nth consecutive time interval if the cumulative amount of energy supplied from the beginning of the nth time interval exceeds a threshold energy. Limiting the supply of power energy to the heater assembly may comprise ceasing the supply of power or energy to the heater assembly.

[0086] Thus, for any or each of the n consecutive time intervals, the amount of energy provided may advantageously not exceed a threshold energy since if the threshold energy is reached, the supply of energy or power may cease until the next time interval. When the power source is fully charged, power may be terminated sooner in the nth consecutive time interval than when the power source is depleted. The more depleted the power source is, the later power may be terminated during any or each of the n consecutive time intervals.

[0087] Similarly, the power, particularly the average power, supplied during any or each of n consecutive time intervals may not exceed the threshold average power, since while the instantaneous power may exceed the threshold average power for one part of the time interval, this can be compensated for by limiting or stopping the power for another part of the time interval.

[0088] The effect of turning off the power may be that power is supplied to the heater assembly in a pulse. The width and height of the pulse may depend on the state of charge of the power source. The width of the pulse may be related to time. The height of the pulse may be related to power. The pulse width may increase as the power source depletes. The pulse height may decrease as the power source depletes.

[0089] A number of n successive pulses may be delivered to the heater assembly while the controller is configured to limit the power or energy. If n is sufficiently high and the duration of any or each of the n successive time intervals is sufficiently low, the pulses may advantageously be seen to result in a continuous delivery of limited power.

[0090] The cumulative amount of energy delivered from the beginning of the nth time interval may not exceed the threshold energy in some cases. There may be reasons for the controller to be configured not to deliver power to the heater assembly during at least a portion of the nth time interval beyond the power or energy limitations described above. For example, as described below, the controller may also be configured to implement thermostatic control of the heater assembly. This may include ceasing power from being delivered to the heater assembly when the heater assembly exceeds a target temperature. Thus, for any of the n subsequent time intervals that at least partially overlap with the thermostatic control, the cumulative amount of energy may not reach the threshold energy. If the cumulative energy does not reach the threshold energy during one of the n consecutive time intervals, the controller may still proceed to the n+1 interval.

[0091] Similarly, the power supplied to the heater assembly during any or each of n consecutive time intervals may be less than the threshold average power.

[0092] The controller configured to monitor the cumulative amount of energy may be configured such that the controller repeatedly measures the instantaneous power supplied from the power source to the heater assembly during any or each of n successive time intervals.

[0093] Measuring the instantaneous power may include the controller being configured to determine the voltage and current supplied to the heater assembly and multiplying the determined voltage by the determined current. Thus, the aerosol generating device may further comprise a voltmeter and an ampere meter, referred to herein as an ammeter. The controller may be configured to determine the voltage based on a signal from the voltmeter and to determine the current based on a signal from the ammeter.

[0094] For each measurement of instantaneous power, the controller may be configured to determine the energy delivered to the heater assembly since the previous measurement of instantaneous power by multiplying the measured instantaneous power by the time that has elapsed since the previous measurement of instantaneous power. This assumes that the instantaneous power measurements can be extrapolated between measurements. The instantaneous power measurements may be made frequently enough that this assumption holds true.

[0095] The controller may comprise a memory for storing a value representative of the accumulated amount of energy. For each measurement of the instantaneous power, the controller may be configured to add the determined energy to the value representative of the accumulated amount of energy. Thus, the value representative of the accumulated amount of energy may advantageously be updated continuously as energy is supplied to the heater assembly. The value representative of the accumulated amount of energy may advantageously provide a running total of energy that can be compared to a threshold energy.

[0096] The controller may be configured to measure the instantaneous power delivered to the heater assembly at least 100 times per second. Preferably, the controller may be configured to measure the instantaneous power delivered to the heater assembly at least 500 times per second.

[0097] The controller may be configured to measure the instantaneous power delivered to the heater assembly less than 10,000 times per second. Even more preferably, the controller may be configured to measure the instantaneous power delivered to the heater assembly less than 5,000 times per second.

[0098] As discussed above, it may be advantageous to measure the instantaneous power frequently, e.g., 500 times per second, so that the assumption holds that the instantaneous power can be extrapolated between measurements. However, making measurements frequently, e.g., 10,000 times per second, can be computationally expensive and introduce other errors. Most preferably, the controller may be configured to measure the instantaneous power delivered to the heater assembly about 1000 times per second.

[0099] The controller may be configured to reset the accumulated amount of energy at the end of n successive time intervals. In particular, the controller may be configured to set a value representing the accumulated amount of energy to zero at the end of any or each of the n successive time intervals.

[0100] Each of the n successive time intervals may be of equal length, which is advantageously the computationally simplest arrangement.

[0101] The duration of each of the n consecutive time intervals may be 10 seconds or less, preferably 1 second or less, preferably 500 milliseconds or less, even more preferably 100 or less, even more preferably 75 milliseconds or less. Most preferably, the duration of each of the n consecutive time intervals may be about 50 milliseconds. n may be greater than 10. Preferably, n may be greater than 50. Preferably, n may be greater than 100. More preferably, n may be greater than 1000. Even more preferably, n may be greater than 5000. As mentioned above, these durations are sufficiently low and n is sufficiently large so that the pulse power appears continuous. Of course, the value of n may be determined primarily by the length of the portion of the usage session to which the power or energy limit applies, and the length of each of the consecutive time intervals.

[0102] The portion of the use session that is divided into n consecutive time intervals may be at least 5 seconds of the use session, preferably at least 10 seconds of the use session, and even more preferably at least 15 seconds of the use session. In other words, the controller may advantageously be configured to limit the supply of power or energy to the heater assembly for at least 5, 10, or 15 seconds.

[0103] The portion of the use session divided into n consecutive time intervals may be at least a pre-heating portion of the use session. In other words, the controller may advantageously be configured to limit the power or energy supplied to the heater assembly during the pre-heating portion of the use session. The pre-heating phase may correspond to an early stage of the use session. In the pre-heating phase, the temperature of the heating element may be raised from ambient or room temperature to a much higher temperature at which substantial aerosols are generated. This may therefore be the period of the use session that has the highest power requirements and may be most affected by a depleted power supply. It may therefore be particularly preferred to limit the power or energy supplied to the heater assembly in the pre-heating.

[0104] The portion of the usage session that is divided into n consecutive time intervals may begin at the beginning of the usage session.

[0105] The controller may also be configured to enforce power or energy limiting after a pre-heating phase.Substantially the entire usage session may be divided into n consecutive time intervals.

[0106] The resistance of the heater element may be at least 0.9 ohms.

[0107] The aerosol generating device may include a temperature sensor configured to measure the temperature of the heater element. The controller may use the temperature measurement to make decisions regarding control of the power supply. Providing a separate temperature sensor may provide a simple and low-cost means for determining the temperature of the heater element. For example, providing a separate temperature sensor eliminates the need to provide a heater element with a high temperature-dependent resistance. The temperature sensor may be a Pt1000 temperature sensor.

[0108] During at least a portion of the use session, the controller may be configured to control the supply of power to the heater assembly such that the heater element is heated with reference to one or more target temperatures.The controller may be configured to control the supply of power to the heater assembly such that the heater element is heated with reference to one or more target temperatures throughout the entire use session.

[0109] The one or more target temperatures may be selected as temperatures at which the aerosol-forming substrate is heated in such a way that it generates a substantial aerosol. The one or more target temperatures may be selected as suitable for a particular type of aerosol-forming substrate. The one or more target temperatures may advantageously be selected to ensure that a consistent amount of aerosol is generated throughout the main phase of a use session. For example, the target temperature may be increased throughout a use session to allow for depletion of the aerosol-forming substrate. This may mean that a user may inhale a consistent amount of aerosol every time they puff on the aerosol generating device.

[0110] Controlling the supply of power to the heater assembly such that the heater element is heated with reference to one or more target temperatures may include the controller being configured to implement thermostat control. In particular, the controller may be configured to implement thermostat control with reference to one or more target temperatures. When there is more than one target temperature, different target temperatures may be used at different times. For example, initially, thermostat control may be performed with reference to a first target temperature. Thereafter, thermostat control may be performed with reference to a second target temperature.

[0111] Thermostatic control may involve a controller repeatedly determining the temperatures of the heater elements and comparing the temperatures to respective target temperatures.

[0112] The controller may be configured to limit or cut off power to the heater assembly while the determined heater element temperatures exceed their respective target temperatures. The heater elements may then be allowed to cool during the time that power is limited or cut off such that the temperature heater elements approach their respective target temperatures.

[0113] The controller may be configured to supply power to the heater assemblies while the determined temperatures of the heater elements are below their respective target temperatures. The heater elements may then be heated while power is supplied such that the temperatures of the heater elements approach their respective target temperatures.

[0114] The controller may be configured to execute the thermostat control during a portion of the usage session that is divided into n consecutive time intervals. The controller may be configured to determine a temperature of the heater track and compare the temperature to a respective target temperature multiple times during at least some of the n consecutive time intervals. During any portion of the usage session that overlaps with the portion of the usage session in which the thermostat control is divided into n consecutive time intervals, the controller may be configured to execute both the thermostat control and the power or energy limiting described above. If the power or energy limiting is implemented by monitoring a cumulative amount of energy, as described above, the cumulative energy may reach the threshold energy only during any or each of the n consecutive time intervals of the time interval in which the thermostat control requires power to be supplied to the heater assembly.

[0115] The controller may be configured to determine the temperature of the heater elements and compare the temperature to the respective target temperatures frequently enough to reduce oscillation effects that may otherwise cause the power to be turned off and on frequently. In particular, this should often be sufficient to ensure that the temperature of the heater assemblies does not oscillate more than 5 degrees Celsius or 6 degrees Celsius above the respective target temperatures, preferably less than 2 degrees Celsius. Furthermore, frequent determination and comparison of the temperature of the heater elements may advantageously ensure that the heater elements do not exceed their respective target temperatures. The controller may be configured to determine the temperature of the heater elements and compare the temperature to the respective target temperatures at least 100 times per second, preferably at least 500 times per second, and even more preferably about 1000 times per second.

[0116] The controller may be configured to determine the temperature of the heater element and compare the temperature to a respective target temperature less than 10,000 times per second, preferably less than 5000 times per second.

[0117] The use session may include a number of successive stages between a use session start and a use session stop. Each stage of the number of successive stages may begin at a stage start time and end at a stage end time. The progression of the use session through the number of successive stages may be controlled by a controller. Preferably, the progression of the use session through the number of successive stages may be controlled by the controller determining at least one of: a length of time from a stage start is equal to or greater than a predetermined duration, and a temperature is equal to or greater than a target temperature.

[0118] During each stage, the controller may be configured to control the power supply to the heater element such that the heater element is heated with reference to a target temperature. The target temperature of each stage may be referred to as a stage target temperature. The stage target temperature of a particular stage may have the same value or a different value compared to the stage target temperature of a subsequent or previous stage.

[0119] Several successive stages are a first stage having a first stage target temperature and a first stage end a first predetermined time after the first stage start; a second stage having a second stage target temperature, the second stage terminating when the controller determines that the temperature of the heater element is equal to or greater than the second target temperature or when the controller determines that the time elapsed since the second stage commencement is equal to or greater than a second predetermined time, whichever occurs first; a third stage having a third stage target temperature, the controller being configured to repeatedly measure the temperature of the heater element to determine a rate of change of temperature of the heater element.

[0120] The multiple consecutive stages may include any combination of first, second, and third stages in any order. For example, the first stage may not have to come chronologically first. The multiple stages may include a first and a second stage, and the first stage may begin before or after the second stage begins.

[0121] The plurality of successive stages may include further stages in addition to at least one of the first to third stages. A use session including any of the first, second and third stages preferably includes those stages towards the start of the use session. An initial part of a use session including any of the first, second and third stages may be referred to as a pre-heating stage. In the pre-heating stage, the aerosol generating device may be configured to rapidly heat the heater track towards an operating temperature at which a substantial aerosol is generated from the aerosol-forming substrate.

[0122] The plurality of successive stages may include a first stage. The start of the first stage may correspond to the start of a usage session.

[0123] The first stage may have a fixed length, with the first stage end being a first predetermined time after the first stage start. As such, the controller may be configured to progress through the first stage based on time rather than temperature. This may be particularly preferred when the first stage is part of a pre-heat stage, since advantageously a minimal amount of energy is delivered to the heater element during that period.

[0124] The multiple successive stages may include a second stage.

[0125] The second stage may have a dynamic length up to a maximum length, since the end of the second stage is the earlier of the controller determining that the temperature of the heater element is equal to or greater than the second stage target temperature, or the controller determining that the time elapsed since the start of the second stage is equal to or greater than a second predetermined time. This may mean that the length of the second stage can be varied depending on how quickly the heater element reaches the second stage target temperature. This may be particularly advantageous when the second stage is part of a pre-heat stage.

[0126] As mentioned above, during the pre-heating stage, the temperature of the heater element may be increased from an initial temperature at the beginning of the use session to an operating temperature at which substantial aerosol is generated from the aerosol-forming substrate. The initial temperature of the heater element may vary. The initial temperature may be equal to ambient or room temperature. However, if the current use session is a short time after a previous use session, the initial temperature of the heater element may be significantly higher than ambient or room temperature. This is because the heater element may store residual heat from the previous use session. By providing a dynamic second stage as part of the pre-heating stage, the difference in initial temperature may be advantageously taken into account. As the initial temperature increases, the heater element may reach the operating temperature and the second stage target temperature more quickly during the pre-heating stage. Because the second stage is dynamic, the second stage does not continue for a fixed period of time, but rather ends when the second stage target temperature is reached. This advantageously reduces the overall length of the pre-heating stage. This may advantageously mean that the aerosol generating device is more quickly ready for inhalation of the aerosol by the user during a usage session, as well as reducing power consumption, which is important when the power source is a portable power source such as a rechargeable battery.

[0127] The multiple successive stages may include a first stage and a second stage. The combination of the first and second stages may be particularly preferred, especially when the first and second stages are part of a preheating stage. As mentioned above, the dynamic second stage may reduce the overall length of the preheating stage. However, it may be advantageous to include an additional fixed length first stage to ensure that a minimum amount of energy is transferred to the heater element even if the initial temperature of the heater element is high. This may be because the preheating stage needs to overcome the latent heat of vaporization in order for the aerosol to be released from the aerosol-forming substrate. Therefore, a minimum amount of energy may need to be transferred to the aerosol-forming substrate to generate the aerosol, which may not be enough for the heater element to reach the target temperature. The combination of a fixed first stage and a dynamic second stage may ensure that a minimum amount of energy is transferred to the heater element even if the target temperature is reached very quickly.

[0128] Preferably, the start of the second phase may correspond to the end of the first phase, in other words the controller may be configured to progress through the first phase and then the second phase, in which case the start of the first phase may correspond to the start of the usage period.

[0129] Alternatively, the start of the first phase may correspond to the end of the second phase, or in other words, the controller may be configured to progress through the second phase and then the first phase, in which case the start of the second phase may correspond to the start of the usage period.

[0130] The plurality of successive stages may include a third stage. In the third stage, the controller may be configured to repeatedly determine the temperature of the heater element to determine a rate of change of the temperature of the heater element. During the third stage, the controller may be further configured to control the power supply to the heater assembly to maintain the rate of change of the temperature of the heater element at a constant value. The third stage may be particularly advantageous when the aerosol generating device includes a temperature sensor for measuring the temperature of the heater element. The temperature sensor may be a separate component.

[0131] When the aerosol generating device includes a temperature sensor, there may be a misalignment between the change in temperature of the heater element and the change registered by the temperature sensor. This may be because it may take time for the energy from the heater element to be transferred to the temperature sensor, and therefore the temperature of the temperature sensor may not represent the temperature of the heater element. The misalignment may be taken into account because the value of the rate of change may be selected to allow the temperature of the temperature sensor to more closely follow the actual temperature of the heater element by controlling the power supply to the heater assembly to maintain a constant rate of change of temperature. This may be because the rate of change of temperature may not be able to significantly exceed the rate of energy transfer from the heater element to the temperature sensor. A suitable range of values ​​for the constant rate of change may be 1-15 degrees Celsius per second. Preferably, the constant rate of change may be 2-10 degrees Celsius per second. Even more preferably, the constant rate of change may be about 3 degrees Celsius per second.

[0132] By accounting for the offset between the change in temperature of the heater element and that change registered by the temperature sensor, the third stage may advantageously reduce or minimize the risk of overheating of the heater element. Without controlling the rate of change and accounting for the offset, the temperature of the heater element may substantially exceed the target temperature by the time the temperature measured by the temperature sensor reaches the target temperature. Implementing a third stage of control may advantageously address this issue. Reducing or minimizing overheating may advantageously prevent damage to the heater assembly and overheating of the aerosol-forming substrate.

[0133] The third stage may be dynamic in length or fixed in length.

[0134] The end of the third phase may be a third predetermined time after the start of the third phase.

[0135] Alternatively, the end of the third stage may be when the controller determines that the temperature of the heater element is equal to or greater than the third stage target temperature.

[0136] Alternatively, the third stage may end when the controller determines that the temperature of the heater element is equal to or greater than the third stage target temperature, or when the controller determines that the time elapsed since the third stage began is equal to or greater than a third predetermined time, whichever occurs first.

[0137] The multiple successive stages may include a first stage and a third stage.

[0138] The start of the third phase may correspond to the end of the first phase.

[0139] The multiple successive stages may include a second stage and a third stage.

[0140] The third stage may correspond to the end of the second stage.

[0141] The multiple consecutive stages may include a first stage, a second stage, and a third stage. The first, second and third stages may be consecutive to one another.

[0142] The third phase may correspond to the end of the second phase, or alternatively, the beginning of the third phase may correspond to the first phase.

[0143] The combination of a third stage with at least one of the first and second stages may be advantageous, especially when the third stage is after at least one of the first or second stages and each of the stages is part of a preheating stage. This may be because during the first or second stages the temperature of the heater element may advantageously heat up quickly, without any specific control related to the rate of change of temperature. Providing a third stage after the first or second stage may advantageously take into account any overheating that may have occurred during the first or second stages. The third stage may advantageously allow time for the temperature sensor to reach equilibrium with the heater element after the first or second stage.

[0144] Preferably, the first stage temperature target and the second stage temperature target may be lower than the third stage temperature target. The first stage temperature target and the second stage temperature target may be sufficiently low so that even if the actual temperature exceeds the temperature target due to a deviation between the actual temperature and the measured temperature, the actual temperature is still lower than the maximum temperature at which the heater assembly is designed to operate. For example, at least one of the first and second stage target temperatures may be at least 10, 20, 30, 40, 50, 60, or 70 degrees Celsius lower than the third stage target temperature. The third stage target temperature may still be lower than the maximum temperature at which the heater assembly is designed to operate. Thus, the actual temperature of the heater element may exceed the first or second stage target temperature by up to 10, 20, 30, 40, 50, 60, or 70 degrees.

[0145] In summary, by combining at least one of the first and second stages with a third stage, the heater element can advantageously be heated rapidly to a target temperature that is low enough that the risk of overheating is minimized, and then heated more slowly to a higher target temperature during the third stage to avoid further overheating.

[0146] The controller may be configured to limit the supply of energy or power to the heater assembly throughout at least one of the first, second and third stages. As used herein, "limiting the supply of energy or power to the heater assembly" refers to at least a portion of a usage session being divided into n consecutive time intervals, and the controller is configured to limit the energy or power supplied to the heater element during any or each of the n consecutive time intervals to a threshold energy or power, as described above.

[0147] The multiple successive stages may include a first stage, and the controller may be configured to limit the supply of power or energy throughout the first stage.

[0148] Alternatively, or additionally, the multiple successive stages may include a second stage, and the controller may be configured to limit the supply of power or energy throughout the second stage.

[0149] Alternatively, or additionally, the plurality of successive stages may include a third stage, and the controller may be configured to limit the supply of power or energy throughout the third stage.

[0150] The controller may be configured to limit the supply of power or energy throughout each of a number of successive stages.

[0151] Each of the first, second and third stage target temperatures may be less than 280 degrees Celsius.

[0152] Each of the first, second and third stage target temperatures may be between 180 degrees Celsius and 265 degrees Celsius.

[0153] The first predetermined time may be between 3 seconds and 20 seconds, preferably between 5 and 10 seconds.

[0154] The second predetermined time may be between 5 seconds and 15 seconds.

[0155] The heater assembly may be configured to externally heat the aerosol-forming substrate.

[0156] The aerosol generating device may further comprise a housing. The housing may define a cavity for receiving the aerosol-forming substrate. The heater assembly may surround at least a portion of the housing that defines the cavity. Alternatively, the heater assembly may define at least a portion of the cavity such that the heater assembly is external to the aerosol-forming substrate in which it is received.

[0157] The heater assembly may be a flexible heater assembly. The heater assembly may comprise at least one layer of flexible support material. The heater element may comprise at least one heater track deposited on the at least one layer of flexible support material. The at least one heater track may form the heater element. The flexible support material may include or consist of polyimide.

[0158] Alternatively, the heater assembly may be configured to heat the aerosol-forming substrate internally.

[0159] The heater element may be formed on a blade configured to penetrate the aerosol-forming substrate.

[0160] The heater element may be configured to be resistively heated. In this case, the heater assembly may be a resistive heating assembly. The heating element of the resistive heating assembly may include or be formed from any material having suitable electrical and mechanical properties. Suitable materials include, but are not limited to, semiconductors such as doped ceramics, "conductive" ceramics (e.g., molybdenum disilicide, etc.), carbon, graphite, metals, alloys, and composites made of ceramic and metallic materials. Such composites may include doped or undoped ceramics. Examples of suitable doped ceramics include doped silicon carbide. Examples of suitable metals include titanium, zirconium, tantalum, and platinum group metals. Examples of suitable alloys include stainless steel, constantan, nickel-containing, cobalt-containing, chromium-containing, aluminum-containing, titanium-containing, zirconium-containing, hafnium-containing, niobium-containing, molybdenum-containing, tantalum-containing, tungsten-containing, tin-containing, gallium-containing, manganese-containing, and iron-containing alloys, and nickel, iron, cobalt, stainless steel-based superalloys, Timetal®, iron-aluminum-based alloys, and iron-manganese-aluminum-based alloys. Timetal® is a registered trademark of Titanium Metals Corporation. The heater element may be coated with one or more electrical insulators. Preferred materials for the heater element may be 304, 316, 304L, 316L, 18SR stainless steel, and graphite.

[0161] The term "aerosol-forming substrate" as used herein refers to a substrate capable of releasing volatile compounds capable of forming an aerosol. Such volatile compounds may be released by heating the aerosol-forming substrate. The aerosol-forming substrate may conveniently be part of an aerosol-generating article or a smoking article.

[0162] The aerosol-forming substrate may be a solid aerosol-forming substrate. Alternatively, the aerosol-forming substrate may comprise both solid and liquid components. The aerosol-forming substrate may comprise a tobacco-containing material that contains volatile tobacco flavour compounds that are released from the substrate upon heating. Alternatively, the aerosol-forming substrate may comprise a non-tobacco material. The aerosol-forming substrate may further comprise an aerosol former that facilitates the formation of a dense and stable aerosol. Examples of suitable aerosol formers are glycerin and propylene glycol.

[0163] The aerosol-forming substrate may comprise an assembly of crimped sheets of homogenized tobacco material. As used herein, the term "crimped sheet" means a sheet having a plurality of substantially parallel ridges or corrugations. Alternatively, or additionally, the aerosol-forming substrate may comprise strands, strips of sheds of homogenized tobacco material. Preferably, the aerosol-forming substrate may comprise cut homogenized tobacco containing glycerin. The glycerin may be applied to the cut homogenized tobacco. Preferably, the glycerin may be sprayed onto the homogenized tobacco.

[0164] The aerosol generating system may comprise a cartridge containing the aerosol-forming substrate. The cartridge may be receivable in a chamber of an aerosol generating device. The aerosol-forming substrate may be solid or liquid, or may contain both solid and liquid components. Preferably, the aerosol-forming substrate is a liquid.

[0165] The aerosol-forming substrate may comprise a plant-derived material. The aerosol-forming substrate may comprise tobacco. The aerosol-forming substrate may comprise a tobacco-containing material that contains volatile tobacco flavour compounds that are released from the aerosol-forming substrate upon heating. Preferably, the aerosol-forming substrate may alternatively comprise a non-tobacco-containing material.

[0166] In a further aspect, there is provided an aerosol generation system comprising an aerosol generating device as described in any aspect disclosed herein. The aerosol generation system may further comprise an aerosol-generating article comprising an aerosol-forming substrate.

[0167] The aerosol-generating article may be in the shape of a rod. The aerosol-forming substrate may be comprised at the distal end of the rod. The proximal end of the rod may form or comprise a mouthpiece. In other words, the aerosol-generating article may comprise a mouthpiece.

[0168] The aerosol-generating article may include a wrapper surrounding the aerosol-forming substrate.

[0169] The aerosol generating device may comprise a housing defining a cavity for receiving an aerosol-forming article. The cavity may be the same as the cavity described in relation to the previous embodiment. In use, when an aerosol-generating article is received in the cavity, a mouthpiece of the aerosol-generating article may protrude from the device. Thus, a user may be able to draw air through the mouthpiece through the aerosol-forming article received in the cavity.

[0170] In a further aspect, there is provided a method of controlling power supplied to a heater assembly of an aerosol generating device during a use session. The aerosol generating device may comprise a heater assembly. The heater assembly may comprise a heater element for heating the aerosol-forming substrate. The aerosol generating device may comprise a power source. The power source may be configured to supply power to the heater assembly.

[0171] The method may include dividing at least a portion of a usage session into n consecutive time intervals.

[0172] The method may further include limiting the power supplied to the heater assembly during any or each of the n consecutive time intervals. The power may be limited to a threshold average power as described in connection with other aspects above.

[0173] Limiting the power supplied to the heater assembly may include limiting the power during any or each of n consecutive time intervals such that an average of the power supplied throughout any or each of the n consecutive time intervals does not exceed a threshold average power.

[0174] The method may include limiting power supplied to the heater assembly during any or each of n consecutive time intervals so as not to exceed a threshold energy for that time interval. Preferably, the threshold energy is not exceeded for each of the n consecutive time intervals. The power source may be a portable power source for storing energy. The portable power source may be a battery, for example a rechargeable battery.

[0175] The threshold energy may be less than the maximum energy that can be delivered by the power source during any or each of the n consecutive time intervals when the power source is fully charged. The threshold energy may advantageously be selected as the amount of energy that the portable power source can provide during any or each of the n consecutive time intervals, even after at least 5, at least 10, at least 15, or even at least 20 usage sessions. For example, the threshold energy may be at least 10% lower than the maximum energy. Preferably, the threshold energy may be at least 15% lower than the maximum energy. Even more preferably, the threshold energy may be at least 20% lower than the maximum energy.

[0176] The threshold energy may be less than 1 Joule, preferably less than 0.8 Joule, and even more preferably less than 0.6 Joule, supplied to the heater assembly during any or each of n consecutive time intervals.

[0177] The threshold energy may be greater than 0.4 Joules, preferably greater than 0.45 Joules, and even more preferably greater than 0.5 Joules.

[0178] The threshold power may be less than the maximum power that can be delivered by the power source during any or each of the n consecutive time intervals when the power source is fully charged. The threshold power may advantageously be selected as the amount of power that the portable power source can provide during any or each of the n consecutive time intervals, even after at least 5, at least 10, at least 15, or even at least 20 usage sessions. For example, the threshold power may be at least 10% lower than the maximum power. Preferably, the threshold power may be at least 15% lower than the maximum power. Even more preferably, the threshold power may be at least 20% lower than the maximum power.

[0179] The threshold average power may be less than 13 Watts, preferably less than 12 Watts, and even more preferably less than 11 Watts. The threshold average power may be greater than 8 Watts, preferably greater than 9 Watts, and even more preferably greater than 10 Watts.

[0180] The power source may store sufficient power for at least 5 usage sessions, preferably at least 10, and even more preferably at least 20 usage sessions.

[0181] The step of limiting the power or energy supplied to the heater assembly during any or each of n consecutive time intervals may include monitoring a cumulative amount of energy supplied to the heater assembly from the beginning of the nth time interval.

[0182] The step of limiting the power or energy supplied to the heater assembly during any or each of the n consecutive time intervals may further include limiting the supply of power or energy to the heater assembly until the end of the n consecutive time interval if a cumulative amount of energy supplied from the beginning of the nth consecutive time interval equals or exceeds a threshold energy. Limiting the supply of power or energy to the heater assembly may comprise ceasing the supply of power energy to the heater assembly.

[0183] The step of monitoring the cumulative amount of energy supplied to the heater assembly from the beginning of the nth time interval may include repeatedly measuring the instantaneous power supplied from the power source to the heater assembly during any or each of the n successive time intervals.

[0184] The step of measuring the instantaneous power may include determining a voltage and a current supplied to the heater assembly, and multiplying the determined voltage by the determined current. The method may further include, for each measurement of instantaneous power, determining an energy supplied to the heater assembly from a previous measurement of the instantaneous power by multiplying the measured instantaneous power by the time elapsed since the previous measurement of the instantaneous power. The method may further include adding the determined energy to a value representing a cumulative amount of energy.

[0185] The method steps relating to measuring instantaneous power and monitoring accumulated energy may be repeated at least 100 times per second, preferably at least 500 times per second, and even more preferably about 1000 times per second.

[0186] The method may further include controlling power supply to the heater assembly such that the heater element is heated with reference to one or more target temperatures during at least a portion of the usage session, which may be for the entire usage session.

[0187] The step of controlling the supply of power to the heater assembly such that the heater elements are heated with reference to one or more target temperatures may include performing a thermostatic control. The thermostatic control may include repeatedly determining a temperature of the heater elements and comparing the temperature with the respective target temperatures. The thermostatic control may include limiting, or preferably halting, the supply of power to the heater assembly while the determined temperature of the heater elements exceeds the respective target temperatures. The thermostatic control may include supplying power to the heater assembly while the determined temperature of the heater elements is lower than the respective target temperatures.

[0188] Thermostatic control may be performed during a portion of a usage session that is divided into n consecutive time intervals.

[0189] A usage session may include multiple successive phases between a usage session start and a usage session stop, where each phase of the multiple successive phases may begin at a phase start time and end at a phase end time.

[0190] The method may further include controlling progression of the use session through a number of successive stages by determining at least one of: a length of time from start of a stage is equal to or greater than a predetermined duration, and a temperature is equal to or greater than a target temperature.

[0191] The plurality of successive stages may include at least one of a first stage, a second stage, and a third stage. The first, second and third stages may be as described above.

[0192] The method may include terminating the first stage at a first predetermined time after initiation of the first stage.

[0193] The method may include terminating the second stage upon the earlier of determining that the temperature of the heater element is equal to or greater than the second stage target temperature or determining that the time elapsed since initiation of the second stage is equal to or greater than a second predetermined time.

[0194] The method may include repeatedly determining the temperature of the heater element during the third stage to determine a rate of change of temperature of the heater element. The method may further include controlling the supply of power to the heater assembly during the third stage to maintain the rate of change of temperature of the heater element at a constant value. The constant value may be between 1 and 15 degrees Celsius per second, preferably between 2 and 10 degrees Celsius per second, and even more preferably about 3 degrees Celsius per second.

[0195] The method may include terminating the third stage when the temperature of the heater element is equal to or greater than the third stage target temperature.

[0196] Alternatively, the method may include terminating the third phase when the time elapsed since initiation of the third phase is equal to or greater than a third predetermined time.

[0197] Alternatively, the method may include terminating the third stage when the temperature of the heater element is equal to or greater than a third target temperature or when the time elapsed since initiation of the third stage is equal to or greater than a third predetermined time, whichever occurs first.

[0198] In a further aspect, there is provided a method of using the aerosol generating device described above.

[0199] In a further aspect, there is provided an aerosol generating device for generating an aerosol from an aerosol-forming substrate. The aerosol generating device may be configured to generate an aerosol during a use session. The aerosol generating device may comprise a timer. The aerosol generating device may comprise a heater assembly. The heater assembly may comprise a heater element for heating the aerosol-forming substrate. The aerosol generating device may comprise a power source. The power source may be configured to provide energy to the heater element. The aerosol generating device may comprise a controller.

[0200] The aerosol generating device of any embodiment described herein may include features described in relation to any other embodiment, except where the incorporation of such features would cause a contradiction with the broadest description made in relation to that embodiment.

[0201] In particular, the use session may progress through a number of successive stages between a use session start and a use session stop. The progression of the use session through the number of successive stages may be performed by a controller. Each of the stages may be initiated at a stage start. Each of the stages may be terminated at a stage end. During each stage, the controller may be configured to control the supply of power to the heater assemblies such that the heater elements are heated with reference to their respective target temperatures.

[0202] The plurality of successive stages may include a first stage. The first stage may have a first stage target temperature. The end of the first stage may be a first predetermined time after the start of the first stage.

[0203] The plurality of successive stages may include a second stage. The second stage may have a second stage target temperature. The second stage may end when the controller determines that the temperature of the heater element is equal to or greater than the second stage target temperature or when the controller determines that the time elapsed since the second stage began is equal to or greater than a second predetermined time, whichever occurs first.

[0204] The first and second stages may be as described above. The plurality of successive stages may further include a third stage. The third stage may be as described above.

[0205] The controller of the aerosol generating device may be further configured such that at least a portion of the usage session is divided into n consecutive time intervals, and to limit the energy or power supplied to the heater element during any or each of the n consecutive time intervals to a threshold energy or power, respectively. The energy or power limitations may be the same as those described above.

[0206] The controller may be configured to limit energy or power during at least one of the first and second phases. The controller may be configured to limit energy or power during both the first and second phases. The controller may be configured to limit energy or power throughout an entire usage session.

[0207] In a further aspect, there is provided a method of controlling the progression of a session of use of an aerosol generating device through a number of successive stages, each of which may be at a stage start, and each of which may be at a stage end.

[0208] The aerosol generating device may be an aerosol generating device disclosed in connection with any aspect herein.

[0209] The aerosol generating device may comprise a heater assembly. The heater assembly may comprise a heater element for heating the aerosol-forming substrate. The aerosol generating device may comprise a power source. The power source may be configured to provide energy to the heater assembly.

[0210] The method may include controlling a supply of power to a heater assembly such that a heater element is heated with reference to a first stage target temperature during the first stage.

[0211] The method may include terminating the first stage such that the first stage end is a first predetermined time after the first stage begins.

[0212] The method may include controlling a supply of power to the heater assembly such that during the second stage the heater element is heated with reference to a second stage target temperature.

[0213] The method may include terminating the second stage when the temperature of the heater element is equal to or greater than the second stage target temperature or when the time elapsed since the second stage is equal to or greater than a second predetermined time, whichever occurs first.

[0214] In a further aspect, there is provided a method of using an apparatus according to the aspects described herein.

[0215] In a further aspect, there is provided an aerosol generating device for generating an aerosol from an aerosol-forming substrate. The aerosol generating device may be configured to generate an aerosol during a use session. The aerosol generating device may comprise a timer. The aerosol generating device may comprise a heater assembly. The heater assembly may comprise a heater element for heating the aerosol-forming substrate. The aerosol generating device may comprise a power source. The power source may be configured to provide energy to the heater element. The aerosol generating device may comprise a controller.

[0216] The aerosol generating device of this further aspect may comprise any of the features described in relation to the aerosol generating device of the previous aspect.

[0217] In particular, the use session may progress through a number of successive stages between a use session start and a use session stop. The progression of the use session through the number of successive stages may be performed by a controller. Each of the stages may be initiated at a stage start. Each of the stages may be terminated at a stage end. During each stage, the controller may be configured to control the supply of power to the heater assemblies such that the heater elements are heated with reference to their respective target temperatures.

[0218] The plurality of successive stages may include a first stage. The first stage may have a first stage target temperature. The first stage may end at least one of a first predetermined time after the first stage begins or when the controller determines that the temperature of the heater element is equal to or greater than the first stage target temperature.

[0219] The plurality of successive stages may include a second stage. The second stage may have a second stage target temperature. In the second stage, the controller may be configured to iteratively determine a temperature of the heater element. The controller may be configured to determine a rate of change of the temperature of the heater element. The controller may be configured to control the supply of power to the heater assembly to maintain the rate of change of the temperature of the heater element at a constant value.

[0220] The second phase start may correspond to the end of the first phase. The first phase start may correspond to the start of a usage session.

[0221] Alternatively, the first phase start may correspond to the second phase end. The second phase start may correspond to the use session start.

[0222] The end of the first phase may be the earlier of the controller determining that the temperature of the heater element is equal to or greater than a first target temperature or the controller determining that the time elapsed since the start of the second phase is equal to or greater than a second predetermined time.

[0223] The first step of this embodiment may correspond to the second step of the previous embodiment, as described above. The second step of this embodiment may correspond to the third step of the previous embodiment, as described above.

[0224] The plurality of successive stages may further include a third stage. The third stage may have a third stage target temperature. The end of the third stage may be a third predetermined time after the start of the third stage. The third stage of this embodiment may correspond to the first stage of the previous embodiment.

[0225] The third stage may be after or before the first stage. The third stage may be after or before the second stage.

[0226] The third phase start may correspond to a usage session start. Alternatively, the third phase start may correspond to a first phase end. Alternatively, the third phase start may correspond to a second phase end.

[0227] The controller of the aerosol generating device may be further configured such that at least a portion of the usage session is divided into n consecutive time intervals, and to limit the energy or power supplied to the heater element during any or each of the n consecutive time intervals to a threshold energy or power, respectively. The energy or power limitations may be the same as those described above.

[0228] The controller may be configured to limit energy or power during at least one of the first and second phases. The controller may be configured to limit energy or power during both the first and second phases. The controller may be configured to limit energy or power throughout an entire usage session.

[0229] In a further aspect, there is provided a method of controlling the progression of a use session of an aerosol generating device through a number of successive stages, each of which may be initiated at a stage start time, and each of which may be terminated at a stage end time.

[0230] The aerosol generating device may be an aerosol generating device as described in the previous embodiments.

[0231] The aerosol generating device may comprise a heater assembly. The heater assembly may comprise a heater element for heating the aerosol-forming substrate. The aerosol generating device may comprise a power source. The power source may be configured to provide power to the heater assembly.

[0232] The method may include controlling a supply of power to a heater assembly such that a heater element is heated with reference to a first stage target temperature during the first stage.

[0233] The method may include terminating the first stage a first predetermined time after initiating the first stage or when the temperature of the heater element is at or above a first stage target temperature.

[0234] The method may include controlling a supply of power to the heater assembly such that during the second stage the heater element is heated with reference to a second stage target temperature.

[0235] The method may include repeatedly measuring the temperature of the heater element during the second stage to determine a rate of change of temperature of the heater element, and controlling the supply of power to the heater assembly to maintain the rate of change of temperature of the heater element at a constant value.

[0236] Features described with respect to one aspect may be applied to other aspects of the disclosure.

[0237] The present invention is defined by examples. However, below is provided a non-exhaustive list of non-limiting examples. Any one or more of the features of these examples may be combined with any one or more of the features of other examples, embodiments, or aspects described herein.

[0238] Example 1. 1. An aerosol generation device for generating an aerosol from an aerosol-forming substrate, the aerosol generation device being configured to generate an aerosol during a session of use, the aerosol generation device comprising: A timer and a heater assembly comprising a heater element for heating the aerosol-forming substrate; a power source configured to provide energy to the heater assembly; An aerosol generating device comprising: Example 1a. 1. An electrically operated aerosol generating device, comprising: a heating chamber configured to at least partially receive an aerosol-generating article comprising an aerosol-forming substrate; a heater including at least one heating element configured to externally heat the aerosol-forming substrate; a power source for providing power to the heating element; and an electrical circuit for controlling the supply of power from the power source to the at least one heating element, the electrical circuit comprising: 1. An electrically operated aerosol generating device arranged to control the power provided to the heating element such that during a first period, power is provided such that the temperature of the heating element rises from an initial temperature to a first temperature, during a second period, power is provided such that the temperature of the heating element decreases to a second temperature below the first temperature, and during a third period, power is provided such that the temperature of the heating element increases to a third temperature higher than the second temperature, the first temperature being between 230°C and 270°C. Example 1b. The electrically-actuated aerosol generation device of Example 1a, wherein the aerosol generation device is configured to generate an aerosol during a use session. Example 2. An aerosol generating device as described in Example 1 or Example 1b, wherein at least a portion of a usage session is divided into n consecutive time intervals. Example 3. An aerosol generating device as described in Example 2, wherein the controller is configured to limit the power supplied to the heater assembly during any or each of n consecutive time intervals so as not to exceed a threshold energy for that time interval. Example 4. 4. An aerosol generating device according to any one of Examples 1 to 3, wherein the power source is a portable power source for storing energy, such as a battery, preferably a rechargeable battery. Example 5. An aerosol generating device as described in Example 4, wherein the threshold energy is less than the maximum energy that can be delivered by the power source during any or each of n consecutive time intervals when the power source is fully charged. Example 6. An aerosol generating device as described in Example 5, wherein the threshold energy is at least 10% lower than the maximum energy, preferably at least 15% lower than the maximum energy, and even more preferably at least 20% lower than the maximum energy. Example 7. An aerosol generating device as described in Example 5 or Example 6, wherein the threshold energy is less than 1 Joule, preferably less than 0.8 Joule, and even more preferably less than 0.6 Joule supplied to the heater element during any or each of n consecutive time intervals. Example 8. An aerosol generating device according to any one of Examples 5 to 7, wherein the threshold energy is greater than 0.4 Joules, preferably greater than 0.45 Joules, and even more preferably greater than 0.5 Joules. Example 9. An aerosol generating device as described in any one of Examples 1 to 8, wherein the controller is configured to limit the power supplied to the heater element during any or each of n consecutive time intervals to a threshold average power. Example 10. 10. The aerosol generating device of example 9, wherein the threshold average power is the average power supplied during n consecutive time intervals. Example 11. An aerosol generating device as described in Example 9 or Example 10, wherein the power source is a portable power source, preferably a battery, even more preferably a rechargeable battery. Example 12. 12. An aerosol generating device as described in Example 11, wherein the threshold average power is less than the maximum power that can be delivered by the power source when the power source is fully charged. Example 13. 13. An aerosol generating device as described in Example 12, wherein the threshold average power is at least 10% lower than the maximum power, preferably at least 15% lower than the maximum power, and even more preferably at least 20% lower than the maximum power. Example 14. An aerosol generating device according to any one of Examples 9 to 13, wherein the threshold average power is less than 13 Watts, preferably less than 12 Watts, and even more preferably less than 11 Watts. Example 15. An aerosol generating device according to any one of Examples 9 to 14, wherein the threshold average power is greater than 8 Watts, preferably greater than 9 Watts, and even more preferably greater than 10 Watts. Example 16. An aerosol generating device according to any one of Examples 1 to 15, wherein the power source stores sufficient power for at least 5 usage sessions, preferably at least 10, and even more preferably at least 20 usage sessions. Example 17. An aerosol generating device described in any one of Examples 1 to 16, wherein the controller limiting the power supplied to the heater assembly during any or each of n consecutive time intervals includes a controller configured to monitor the cumulative amount of energy supplied to the heater assembly from the start of the nth time interval. Example 18. An aerosol generating device as described in Example 17, wherein the controller is further configured to limit power supply to the heater assembly until the end of the nth consecutive time interval if the cumulative amount of energy supplied from the start of the nth time interval equals or exceeds the threshold energy. Example 19. 19. The aerosol generating device of Example 18, wherein limiting the power supply to the heater assembly comprises terminating the power supply to the heater assembly. Example 20. An aerosol generating device described in any one of Examples 17 to 19, wherein the controller configured to monitor the cumulative amount of energy includes a controller configured to repeatedly measure the instantaneous power supplied from the power source to the heater assembly during any or each of n consecutive time intervals. Example 21. An aerosol generating device as described in Example 20, wherein measuring the instantaneous power includes a controller configured to determine the voltage and current supplied to the heater assembly and multiplying the determined voltage by the determined current. Example 22. An aerosol generating device as described in Example 21, further comprising a voltage meter and an ammeter, wherein the controller is configured to determine the voltage based on a signal from the voltage meter and to determine the current based on a signal from the ammeter. Example 23. An aerosol generating device as described in Example 20, Example 21, or Example 22, wherein for each measurement of instantaneous power, the controller is configured to determine the energy supplied to the heater assembly from the previous measurement of instantaneous power by multiplying the measured instantaneous power by the time elapsed since the previous measurement of instantaneous power. Example 24. 24. An aerosol generating device as described in Example 23, wherein the controller comprises a memory for storing a value representing the cumulative amount of energy. Example 25. An aerosol generating device as described in Example 24, wherein for each measurement of instantaneous power, the controller is configured to add the determined energy to a value representing the cumulative amount of energy. Example 26. An aerosol generating device described in any one of Examples 20 to 25, wherein the controller is configured to measure the instantaneous power supplied to the heater assembly and monitor the cumulative energy at least 100 times per second, preferably at least 500 times per second, and even more preferably at least about 1,000 times per second. Example 27. An aerosol generating device as described in Example 24, Example 25, or Example 26, wherein the controller is configured to reset the accumulated amount of energy at the end of any or each of n consecutive time intervals. Example 28. 28. An aerosol generating apparatus according to any one of Examples 1 to 27, wherein the end of the nth consecutive time interval corresponds to the start of n+1 consecutive time intervals. Example 29. 29. An aerosol generating apparatus according to any one of Examples 1 to 28, wherein each of the n consecutive time intervals is of equal length. Example 30. 30. An aerosol generating apparatus according to any one of Examples 1 to 29, wherein the duration of each of the n consecutive time intervals is 100 milliseconds or less, more preferably 50 milliseconds or less. Example 31. 31. The aerosol generating apparatus according to any one of Examples 1 to 30, wherein n is greater than 10, preferably greater than 50, preferably greater than 100, more preferably greater than 1000, and even more preferably greater than 5000. Example 32. An aerosol generating device as described in any one of Examples 1 to 31, wherein the portion of the usage session divided into n consecutive time intervals is at least 5 seconds of the usage session, preferably at least 10 seconds of the usage session, and even more preferably at least 15 seconds of the usage session. Example 33. 33. An aerosol generating device according to any one of Examples 1 to 32, wherein a portion of the usage session that is divided into n consecutive time intervals is at least a pre-heating portion of the usage session. Example 34. 34. An aerosol generating device according to any one of Examples 1 to 33, wherein a portion of the usage session divided into n consecutive time intervals starts at the start of the usage session. Example 35. An aerosol generating device according to any one of Examples 1 to 34, wherein substantially the entire usage session is divided into n consecutive time intervals. Example 36. An aerosol generating device according to any one of Examples 1 to 35, wherein the resistance of the heater element is at least 0.9 ohms. Example 37. An aerosol generating device described in any one of Examples 1 to 36, further comprising a temperature sensor configured to measure the temperature of the heater element. Example 38. An aerosol generating device described in any one of Examples 1 to 37, wherein during at least a portion of a usage session, the controller is configured to control the supply of power to the heater assembly so that the heater element is heated with reference to one or more target temperatures. Example 39. An aerosol generating device as described in Example 38, wherein the controller is configured to control the supply of power to the heater assembly so that the heater element is heated with reference to one or more target temperatures throughout the entire usage session. Example 40. An aerosol generating device as described in Example 38 or Example 39, comprising a controller configured to implement thermostatic control and to control the supply of power to the heater assembly so that the heater element is heated with reference to one or more target temperatures. Example 41. An aerosol generating device as described in Example 40, wherein the thermostatic control includes a controller repeatedly determining the temperature of the heater element and comparing the temperature with a respective target temperature. Example 42. An aerosol generating device as described in Example 40 or Example 41, wherein the controller is configured to stop supplying power to the heater assembly while the determined temperature of the heater element exceeds the respective target temperature. Example 43. An aerosol generating device described in any one of Examples 40 to 42, wherein the controller is configured to supply power to the heater assembly while the determined temperature of the heater element is lower than the respective target temperature. Example 44. An aerosol generating device described in any one of Examples 40 to 43, wherein the controller is configured to perform thermostatic control during a portion of a usage session that is divided into n consecutive time intervals. Example 45. An aerosol generating device as described in Example 44, wherein the controller is configured to determine the temperature of the heater track and compare the temperature to each target temperature multiple times during at least a portion of n consecutive time intervals. Example 46. An aerosol generating device described in any one of Examples 41 to 45, wherein the controller is configured to determine the temperature of the heater element and compare the temperature with each target temperature at least 100 times per second, preferably at least 500 times per second, and even more preferably about 1,000 times per second. Example 47. An aerosol generating device described in any one of Examples 41 to 46, wherein the controller is configured to determine the temperature of the heater element and compare the temperature with each target temperature less than 10,000 times per second, preferably less than 5,000 times per second. Example 48. An aerosol generating device as described in any one of Examples 1 to 47, wherein the use session comprises a plurality of successive stages between the start of the use session and the end of the use session. Example 49. 49. An aerosol generating device as described in Example 48, wherein each of the plurality of successive stages begins at the start of the stage and ends at the end of the stage. Example 50. An aerosol generating device as described in Example 49, wherein the progression of a usage session through multiple successive stages is controlled by a controller. Example 51. An aerosol generating device as described in Example 50, wherein the progress of a usage session through multiple successive stages is controlled by a controller that determines at least one of: the length of time from the start of a stage is greater than or equal to a predetermined duration, and the temperature is greater than or equal to a target temperature. Example 52. An aerosol generating device as described in Example 50 or Example 51, wherein during each stage, the controller is configured to control the supply of power to the heater element so that the heater element is heated with reference to a target temperature. Example 53. Several successive stages a first stage having a first stage target temperature and a first stage end a first predetermined time after the first stage start; a second stage having a second stage target temperature, the second stage terminating when the controller determines that the temperature of the heater element is equal to or greater than the second target temperature or when the controller determines that the time elapsed since the second stage commencement is equal to or greater than a second predetermined time, whichever occurs first; An aerosol generating device as described in any one of Examples 50 or 52, comprising at least one of: a third stage having a third stage target temperature, and the controller is configured to repeatedly determine the temperature of the heater element to determine a rate of change of the temperature of the heater element. Example 54. 54. The aerosol generating device of Example 53, wherein the plurality of successive stages comprises a first stage. Example 55. 55. An aerosol generating device as described in Example 54, wherein the initiation of the first phase corresponds to the initiation of a usage session. Example 56. An aerosol generating device as described in Example 54 or Example 55, wherein the multiple successive stages further comprise a second stage. Example 57. 57. The aerosol generating device of Example 56, wherein the start of the second stage corresponds to the end of the first stage. Example 58. An aerosol generating device as described in Example 56 or Example 57, wherein the multiple consecutive stages further include a third stage, and the start of the third stage corresponds to the end of the second stage. Example 59. An aerosol generating device as described in Example 54 or Example 55, wherein the multiple successive stages further comprise a third stage. Example 60. 60. The aerosol generating device of Example 59, wherein the start of the third stage corresponds to the end of the first stage. Example 61. 54. The aerosol generating device of Example 53, wherein the plurality of successive stages includes a second stage. Example 62. An aerosol generating device as described in Example 61, wherein the initiation of the second phase corresponds to the initiation of a usage session. Example 63. An aerosol generating device as described in Example 61 or Example 62, wherein the multiple successive stages include a third stage. Example 64. 64. The aerosol generating device of Example 63, wherein the start of the third stage corresponds to the end of the second stage. Example 65. An aerosol generating device as described in Example 53, wherein the multiple consecutive stages include a third stage and a fourth stage having a fourth stage target temperature, and the end of the fourth stage is a fourth predetermined time after the start of the fourth stage or when the controller determines that the temperature of the heater element is equal to or greater than the fourth stage target temperature. Example 66. 66. The aerosol generating device of Example 65, wherein the fourth stage is the same as the second stage. Example 67. An aerosol generating device described in any one of Examples 53 to 66, wherein in a third stage, the controller is configured to control the power supply to the heater assembly to maintain the rate of change of temperature of the heater element at a constant value. Example 68. 68. The aerosol generating device of Example 67, wherein the constant value is 1 to 15 degrees Celsius per second, preferably 2 to 10 degrees Celsius per second, and even more preferably about 3 degrees Celsius per second. Example 69. An aerosol generating device described in any one of Examples 53 to 66, wherein the end of the third stage is when the controller determines that the temperature of the heater element is greater than or equal to a third target temperature or when the controller determines that the time elapsed since the start of the third stage is greater than or equal to a third predetermined time. Example 70. An aerosol generating device described in any one of Examples 53 to 69, wherein the controller is configured to limit the supply of power to the heater assembly throughout at least one of the first, second, and third stages. Example 71. An aerosol generating device as described in Example 70, wherein the multiple successive stages include a first stage, and the controller is configured to limit power supply throughout the first stage. Example 72. An aerosol generating device as described in Example 71, wherein the controller is configured to limit power supply over each of a plurality of successive stages. Example 73. An aerosol generating apparatus according to any one of Examples 53 to 72, wherein the third target temperature is higher than at least one of the first and second target temperatures. Example 74. An aerosol generating apparatus according to any one of Examples 53 to 73, wherein each of the first, second, and third stage target temperatures is less than 280 degrees Celsius. Example 75. An aerosol generating apparatus according to any one of Examples 53 to 74, wherein each of the first, second and third target stage temperatures is between 180 degrees Celsius and 265 degrees Celsius. Example 76. The aerosol generating apparatus according to any one of Examples 53 to 75, wherein the first predetermined time is 3 to 20 seconds, preferably 5 to 10 seconds. Example 77. The aerosol generating apparatus according to any one of Examples 53 to 76, wherein the second predetermined time is 5 seconds to 15 seconds. Example 78. An aerosol generating apparatus according to any one of Examples 1 to 77, wherein the heater assembly is configured to externally heat the aerosol-forming substrate. Example 79. An aerosol generating device described in any one of Examples 1 to 78, further comprising a housing defining a cavity for receiving the aerosol-forming substrate, wherein the heater assembly surrounds at least a portion of the housing defining the cavity or defines at least a portion of the cavity such that the heater assembly is external to the received aerosol-forming substrate. Example 80. 79. An aerosol generating device as described in Example 79, wherein the heater assembly is a flexible heater assembly. Example 81. An aerosol generating device as described in Example 80, wherein the heater assembly comprises at least one layer of flexible supporting material and the heater element is at least one heater track deposited on the at least one layer of flexible supporting material. Example 82. 82. The aerosol generating device of embodiment 81, wherein the flexible support material comprises or consists of polyimide. Example 83. An aerosol generating device according to any one of Examples 1 to 77, wherein the heater assembly is configured to heat the aerosol-forming substrate from within. Example 84. The aerosol generating device according to any one of Examples 1 to 77, wherein the heater element is formed on a blade configured to penetrate the aerosol-forming substrate. Example 85. 85. An aerosol generating device according to any one of Examples 1 to 84, wherein the heater element is configured to be resistively heated. Example 86. An aerosol-generating system comprising the aerosol-generating device according to any one of Examples 1 to 85, and an aerosol-generating article including an aerosol-forming substrate. Example 87. The aerosol generating system of Example 86, wherein the aerosol generating article is in the form of a rod. Example 88. The aerosol-generating system of Example 87, wherein the aerosol-generating article comprises a wrapper surrounding the aerosol-forming substrate. Example 89. An aerosol generation system described in any one of Examples 86 to 88, wherein the aerosol generation device comprises a housing defining a cavity for receiving an aerosol forming article. Example 90. 1. A method of controlling power supplied to a heater assembly of an aerosol generating device during a use session, the aerosol generating device comprising a heater assembly comprising a heater element for heating an aerosol-forming substrate and a power source configured to supply power to the heater assembly, the method comprising: Dividing at least a portion of a usage session into n consecutive time intervals; and limiting the power supplied to the heater assembly during any or each of n consecutive time intervals so as not to exceed a threshold energy for the time interval. Example 92. 92. The method of example 91, wherein the threshold energy is less than the maximum energy that can be delivered by the power source, which is a portable power source, during any or each of n consecutive time intervals when the power source is fully charged. Example 93. The method of example 92, wherein the threshold energy is at least 10% lower than the maximum energy. Preferably, the threshold energy may be at least 15% lower than the maximum energy. Even more preferably, the threshold energy may be at least 20% lower than the maximum energy. Example 94. The method of any one of Examples 91 to 93, wherein the threshold average power is at least 10% lower than the maximum power, preferably at least 15% lower than the maximum power, and even more preferably at least 20% lower than the maximum power, and the threshold average power is less than 13 Watts, preferably less than 12 Watts, and even more preferably less than 11 Watts. Example 95. The method of any one of examples 91 to 94, wherein the threshold average power is the average power supplied during the nth consecutive time interval. Example 96. The method of any one of Examples 91 to 95, wherein the method includes limiting the energy supplied to the heater assembly during any or each of n consecutive time intervals to a threshold energy. Example 97. 97. The method of example 96, wherein the threshold energy is less than the maximum energy that can be delivered by the power source when the power source is fully charged. Example 98. The method of example 96-example 97, wherein the threshold energy is less than 1 Joule, preferably less than 0.8 Joule, and even more preferably less than 0.6 Joule, delivered to the heater element during each of n consecutive time intervals. Example 99. The method of any one of Examples 96 to 98, wherein the threshold energy is greater than 0.4 Joules, preferably greater than 0.45 Joules, and even more preferably greater than 0.5 Joules. Example 100. The method of any one of Examples 90 to 99, wherein the step of limiting the power supplied to the heater assembly during any or each of n consecutive time intervals includes monitoring the cumulative amount of energy supplied to the heater assembly from the start of the nth time interval. Example 101. The method of example 100, wherein the step of limiting the power supplied to the heater assembly during any or each of n consecutive time intervals further comprises limiting the supply of power to the heater assembly until the end of the nth consecutive time interval if the cumulative amount of energy supplied from the start of the nth consecutive time interval equals or exceeds the threshold energy. Example 102. The method of example 100 or example 101, wherein the step of monitoring the cumulative amount of energy supplied to the heater assembly from the beginning of the nth time interval includes repeatedly measuring the instantaneous power supplied from the power source to the heater assembly during any or each of n consecutive time intervals. Example 103. 103. The method of embodiment 102, wherein the step of measuring the instantaneous power includes determining a voltage and a current supplied to the heater assembly, and multiplying the determined voltage by the determined current. Example 104. 104. The method of example 103, wherein the method further includes, for each measurement of instantaneous power, determining the energy supplied to the heater assembly from a previous measurement of the instantaneous power by multiplying the measured instantaneous power by the time elapsed since the previous measurement of the instantaneous power. Example 105. 105. The method of example 104, wherein the method further comprises adding the determined energy to a value representing the cumulative amount of energy. Example 106. The method of any one of Examples 90 to 105, wherein the method further includes controlling the supply of power to the heater assembly so that the heater element is heated with reference to one or more target temperatures during at least a portion of the usage session. Example 107. The method of embodiment 106, wherein the step of controlling the power supply to the heater assembly such that the heater element is heated with reference to one or more target temperatures includes implementing a thermostatic control. Example 108. The method of example 107, wherein the thermostat control includes repeatedly determining the temperature of the heater element and comparing the temperature to a respective target temperature. Example 109. 109. The method of example 108, wherein the thermostatic control includes limiting, or preferably terminating, the supply of power to the heater assembly while the determined temperatures of the heater elements exceed their respective target temperatures. Example 110. The method of example 108 or example 109, wherein the thermostatic control includes supplying power to the heater assembly while the determined temperatures of the heater elements are below their respective target temperatures. Example 111. A method according to any one of Examples 108 to 110, wherein the thermostat control is performed during a portion of the usage session that is divided into n consecutive time intervals. Example 112. A method described in any one of Examples 90 to 111, wherein the usage session includes a plurality of consecutive stages between a usage session start and a usage session stop, and each of the plurality of consecutive stages starts at a stage start time and ends at a stage end time. Example 113. The method of example 112, further comprising controlling the progression of the usage session through multiple successive stages by determining at least one of: the length of time from the start of a stage is greater than or equal to a predetermined duration; and the temperature is greater than or equal to a target temperature. Example 114. The method according to any one of Examples 90 to 113, wherein the aerosol generating apparatus is the aerosol generating apparatus according to any one of Examples 1 to 89. Example 114. A method of using the aerosol generating device described in any one of Examples 1 to 89. Example 115. an aerosol generating device for generating an aerosol from an aerosol-forming substrate, the aerosol being configured to generate the aerosol during a use session progressing through a number of successive stages between a use session start and a use session stop; A timer and a heater assembly comprising a heater element for heating the aerosol-forming substrate; a power supply configured to provide power to the heater assembly; A controller, the progression of the usage session through a plurality of successive stages is controlled by a controller, each of the stages beginning at a stage start time and ending at a stage end time, the controller being configured to control the supply of power to the heater assembly such that the heater elements are heated with reference to a respective target temperature; Several successive stages a first stage having a first stage target temperature and a first stage end a first predetermined time after the first stage start; a second stage having a second target temperature and the second stage ending when the controller determines that the temperature of the heater element is equal to or greater than the second stage target temperature or when the controller determines that the time elapsed since the second stage begins is equal to or greater than a second predetermined time, whichever occurs first. Example 116. 1. A method of controlling the progression of a use session of an aerosol generating device through a plurality of successive stages, each of the stages beginning at a stage start time and ending at a stage end time, the aerosol generating device comprising a heater assembly comprising a heater element for heating an aerosol-forming substrate and a power source configured to supply power to the heater assembly, the method comprising: controlling power to the heater assembly such that the heater element is heated during the first stage with reference to a first stage target temperature; terminating the first stage such that the first stage end is a first predetermined time after the first stage commencement; controlling power to the heater assembly such that the heater element is heated during the second stage with reference to a second stage target temperature; The second stage is The temperature of the heater element is equal to or greater than the second stage target temperature, or and c) terminating when the time elapsed since the second step is equal to or greater than a second predetermined time, whichever occurs first. Example 117. an aerosol generating device for generating an aerosol from an aerosol-forming substrate, the aerosol being configured to generate the aerosol during a use session progressing through a number of successive stages between a use session start and a use session stop; A timer and a heater assembly comprising a heater element for heating the aerosol-forming substrate; a power supply configured to provide power to the heater assembly; A controller, the progression of the usage session through a plurality of successive stages is controlled by a controller, each of the stages beginning at a stage start time and ending at a stage end time, the controller being configured to control the supply of power to the heater assembly such that the heater elements are heated with reference to a respective target temperature; Several successive stages a first stage having a first stage target temperature and a first stage end being a first predetermined time after the first stage begins or when the controller determines that the temperature of the heater element is equal to or greater than the first stage target temperature; a second stage having a second stage target temperature, the controller being configured to repeatedly measure the temperature of the heater element based on signals received from the temperature sensor to determine a rate of change of temperature of the heater element and control the supply of power to the heater assembly to maintain the rate of change of temperature of the heater element at a constant value. Example 118. An aerosol generating device as described in Example 117, wherein the end of the first stage is the earlier of the controller determining that the temperature of the heater element is equal to or greater than a first target temperature or the controller determining that the time elapsed since the start of the second stage is equal to or greater than a second predetermined time. Example 119. 1. A method of controlling the progression of a use session of an aerosol generating device through a plurality of successive stages, each of the stages beginning at a stage start time and ending at a stage end time, the aerosol generating device comprising a heater assembly comprising a heater element for heating an aerosol-forming substrate and a power source configured to supply power to the heater assembly, the method comprising: controlling power to the heater assembly such that the heater element is heated during the first stage with reference to a first stage target temperature; terminating the first stage a first predetermined time after initiating the first stage or when the temperature of the heater element is equal to or greater than a first stage target temperature; controlling power to the heater assembly such that the heater element is heated during the second stage with reference to a second stage target temperature; repeatedly measuring the temperature of the heater element during the second stage to determine a rate of change of temperature of the heater element and controlling the supply of power to the heater assembly to maintain the rate of change of temperature of the heater element at a constant value.

[0239] The embodiments will now be further described with reference to the following figures: [Brief description of the drawings]

[0240] [Figure 1] FIG. 1 is a schematic cross-sectional view of an aerosol generating device. [Diagram 2] FIG. 2 shows a perspective view of certain features of the aerosol generating device of FIG. 1 separated from the remainder of the device. [Diagram 3] FIG. 3 is a cross-sectional schematic diagram of a heater assembly of an aerosol generating device. [Figure 4] FIG. 4 is a graph depicting the temperature of the heater track of the heater assembly of FIG. 3 versus time during a portion of a first embodiment of a heating routine that may be implemented by a controller of an aerosol generating device. [Diagram 5] FIG. 5 is a graph similar to FIG. 4, but with a higher starting temperature for the heater track. [Figure 6] FIG. 6 is a graph depicting heater track temperature versus time during a portion of a second embodiment of a heating routine that may be implemented by a controller of an aerosol generating device. [Figure 7] FIG. 7 is a graph depicting heater track temperature versus time during a portion of a third embodiment of a heating routine that may be implemented by a controller of an aerosol generating device. [Figure 8] FIG. 8 is a flow diagram illustrating a method for controlling the average power delivered during a 50 millisecond period. [Figure 9] FIG. 9 is a graph illustrating the cumulative energy delivered to the heater track during the 50 millisecond period of FIG. 8 while the method of FIG. 8 is performed. [Figure 10] FIG. 10 is a graph showing the power delivered to the heater track when the power supply is fully charged, during the same 50 millisecond period as FIG. [Figure 11] FIG. 11 is a graph showing the power delivered to the heater track during the same 50 millisecond period as FIG. 9, when the power supply is not fully charged. [Figure 12]FIG. 12 is a graph illustrating the heating profile applied to an aerosol-forming substrate of an aerosol-generating article by an aerosol-generating device according to the embodiment of FIG. 1 during a use session. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0241] 1 is a schematic cross-sectional view of a first aerosol generating device 100. The aerosol generating device 100 comprises a cavity 10 for receiving an aerosol-generating article 200. The cavity 10 is formed by a stainless steel tube 12, having a base 14 at its upstream end.

[0242] The aerosol-generating article 200 is received within the cavity 10. The aerosol-generating article 200 contains an aerosol-forming substrate 202. The aerosol-forming substrate 202 is a solid tobacco-containing substrate. In particular, the aerosol-forming substrate 202 is formed from cut sheets of homogenized tobacco. As shown in Figure 1, the aerosol-generating article 200 and the stainless steel tube 12 are configured such that when the aerosol-generating article is received within the cavity 10, a mouth end of the aerosol-generating article 200 protrudes from the cavity 10 and from the aerosol-generating device. This mouth end forms a mouthpiece 204 through which a user of the aerosol-generating device may draw smoke in use.

[0243] The aerosol generating device 100 together with the aerosol generating article 200 may be referred to as an aerosol generating system.

[0244] The aerosol generating device 100 may further comprise a heater assembly 102. The heater assembly 102 is a multi-layered flexible heater assembly. The layers of the heater assembly 102 are more clearly shown in FIG. 3, as described below. The heater assembly 102 is bent around and surrounds the upstream end of the stainless steel tube 12. The portion of the stainless steel tube 12 surrounded by the heater assembly 102 corresponds to a portion of the cavity 10 in which the aerosol-forming substrate 202 of the aerosol-generating article 200 is received when the aerosol-generating article 200 is received within the cavity 10.

[0245] The heater assembly 102 further comprises a temperature sensor 104. The temperature sensor 104 is a Pt1000 type temperature sensor. The temperature sensor 104 is in thermal contact with the heater track of the heater assembly 102 and is configured to measure the temperature of the heater track of the heater assembly 102.

[0246] 2 more clearly shows the tubular nature of the stainless steel tube 12 with a heater assembly 102 including a temperature sensor 104 wrapped around the lower portion of the stainless steel tube 12. The stainless steel tube 12 and heater assembly 102 are shown separate from the remaining features of the aerosol generation system in FIG.

[0247] 3 is a cross-sectional schematic diagram of the heater assembly 102, showing the various layers of the heater assembly. The thickness of each of the layers is not drawn to scale. From bottom to top, the layers are: a first adhesive layer 110, a first polyimide substrate layer 112, a heating track 114, a second adhesive layer 116, a second polyimide layer 118, and a heat shrink layer 120. The temperature sensor 104 is positioned between the second polyimide layer 118 and the heat shrink layer 120. The temperature sensor 104 includes a connecting wire 105 for connecting the temperature sensor 104 to a controller 108.

[0248] A first adhesive layer 110 is used to adhere the heater assembly 102 to the stainless steel tube 12. Sandwiching the heater track 114 between the first polyimide layer 112 and the second polyimide layer 118 provides a means to support the heater track 114 in place and provides electrical insulation between the heater track 114 and other components of the aerosol generating device 100, particularly the stainless steel tube 12. Polyimide is advantageously flexible, electrically insulating and able to withstand the normal operating temperatures of the aerosol generating device, particularly the heater track 114, in use.

[0249] The heater track 114 is a continuous conductive track of stainless steel that is deposited on one of the first or second polyimide layers 118 during fabrication. The heater track 114 is configured to heat up when an electrical current is passed through the heater track 114. In other words, the heater assembly 102 is a resistively heated heater assembly 102. The heater track 114 has a resistance of 1.1 ohms at room temperature.

[0250] A second adhesive layer 116 holds the first polyimide layer 112 and the second polyimide layer 118 together which keeps the heater track 114 in place.

[0251] The heat shrink layer 120 comprises a material capable of withstanding the normal operating temperatures of the aerosol generating device, in use, and in particular the heater track 114. During manufacture, the heat shrink layer 120 is applied over the components of the heater assembly 102 after they have been wrapped around and adhered to the stainless steel tube 12. The heat shrink layer 120 is heated to a temperature of approximately 320 degrees Celsius as part of the manufacturing process. This ensures that the temperature sensor 104 is in intimate contact with the second polyimide layer 118, and therefore firmly maintained in intimate thermal contact with the heater track 114.

[0252] The aerosol generating device 100 further comprises a power source 106 in the form of a rechargeable battery. The power source 106 and the temperature sensor 104 of the heater assembly 102 are connected to a controller 108 of the aerosol generating device 100 via electrical wires and connections not fully shown in the figure. The power source 106 is configured to power the heater assembly 102 and is connected to a connector of the heater track 102, not shown in the figure. The application of heat by the power source 106 to the heater assembly 102 is controlled by the controller 108.

[0253] The controller 108 further includes a timer, not shown.

[0254] The airflow channel 111 extends from an air inlet 113 of the aerosol generating device 100. Upstream of the cavity, the airflow channel 111 is defined primarily by airflow channel walls 114. Downstream of the airflow channel walls 114, the airflow channel 111 passes through an air inlet defined in the base 14 of the cavity. The airflow channel 111 then extends through the cavity 10. When an aerosol-generating article 200 is received within the cavity 10, the airflow channel 111 passes through the aerosol-generating article 200 and extends through the mouthpiece 204.

[0255] The aerosol generating device may comprise further elements not shown in the figures, such as a button for activating the aerosol generating device.

[0256] During use of the aerosol-generating system, the aerosol-generating article 200 is inserted into the cavity 10 by a user of the system. The user then activates the device. This may be done, for example, by pressing a button or by inhaling through the mouthpiece 204 of the aerosol-generating article, which is detected by a puff sensor, not shown.

[0257] After activation, the controller 108 is configured to control the supply of power from the power supply 106 to the heater assembly 102 to heat the heating track 114. Heat from the heating track 114 is conducted through the stainless steel tube 12 to the aerosol-forming substrate 202 of the aerosol-generating article 200. This heating of the aerosol-forming substrate 202 generates a vapor that is released into the air that is drawn into the aerosol-forming article 200 via the airflow channel 111. The vapor then cools and condenses into an aerosol. Thus, when the user inhales through the mouthpiece, the generated aerosol is drawn through the aerosol-forming article 200 and inhaled by the user.

[0258] Control of heating by controller 108 is based on a temperature signal received from temperature sensor 104 and a timing signal received from a timer, as described in more detail below. Controller 108 may additionally or alternatively be configured to limit the average power provided by power source 106 so as not to exceed a predetermined power level, as described in more detail below.

[0259] 4 shows a graph 300 representing a first embodiment of a portion of a heating routine that may be implemented by the controller 108, whereby the controller controls heating based on temperature and timing signals. The X-axis of the graph represents time in seconds. Zero (t=0) on the X-axis represents the start of a usage session of the aerosol generating device, which begins with a user activating the aerosol generating device. The Y-axis of the graph represents temperature. In particular, the Y-axis of the graph represents the temperature of the heating track 114 as measured by the temperature sensor 104.

[0260] The heating routine portion of FIG. 4 includes four successive steps.

[0261] The first phase 302 begins at 0 seconds. The first phase 302 is of fixed duration, with the first phase ending 15 seconds after the first phase begins. Throughout the first phase 302, the controller 108 is configured to heat the heater track 114 toward a first target temperature of 250 degrees Celsius. 250 degrees Celsius is represented by line 303 in FIG. 4. When heating toward the first target temperature 303, the controller 108 is configured to repeatedly monitor the temperature of the heater track 114 measured by the temperature sensor 104. If the controller 108 determines that the measured temperature is less than the target temperature 303, the controller 108 continues to supply power to the heater assembly 102. If the controller 108 determines that the measured temperature is equal to or greater than the target temperature 303, the controller stops supplying power to the heater assembly 102 until the measured temperature falls below the target temperature. The controller is configured to determine a measured temperature and compare the measured temperature to a target temperature every millisecond.

[0262] In other words, the controller 108 is configured to implement a thermostatic control of the heater assembly 102. In a first stage 302, the target temperature of the thermostatic control is a first target temperature 303, i.e., 250 degrees Celsius.

[0263] Once the controller 108 determines that 15 seconds of the first phase 302 have elapsed, it is configured to proceed to a second phase 304. Thus, the start of the second phase corresponds to the end of the first phase. Throughout the second phase 304, the controller 108 is configured to heat the heater track towards a second target temperature, which in this case is also 250 degrees Celsius, as represented by line 305.

[0264] The second phase 304 is dynamic in length. If at any time during the second phase 304 the controller 108 determines that the temperature of the heater track 114 measured by the temperature sensor 104 exceeds the second target temperature 305, the controller 108 is configured to proceed to the third phase 306. However, the second phase 304 has a maximum length of 10 seconds, so that the second phase ends no later than 10 seconds after the start of the second phase or 25 seconds after the start of the usage session. If the maximum 10 seconds of the second phase 304 elapses before the controller determines that the temperature of the heater track 114 exceeds the second target temperature 305, the controller proceeds to the third phase 306 regardless. In FIG. 4, the controller 108 determined that the heater track 114 reached the second target temperature 305 9 seconds after the start of the second phase, i.e., slightly before the maximum length of the second phase 304. Thus, the end of the second phase is not a maximum of 10 seconds, but approximately 9 seconds after the end of the first phase, i.e. 24 seconds after the start of the use phase.

[0265] The third phase start corresponds to the second phase end. The third phase 306 has a fixed duration, with the third phase end being 5 seconds after the third phase start, or in this case 29 seconds after the use phase start. Throughout the third phase 306, the controller is configured to heat the heater track 114 towards a third target temperature, which is 250 degrees Celsius, as represented by line 307 in FIG. 4, as well as the first and second target temperatures. In the third phase 306, a thermostatic control is used to maintain the heater track 114 at the third target temperature 307.

[0266] Once the controller 108 determines that five seconds of the third phase 306 have elapsed, the controller 108 is configured to transition to a fourth phase 308. Thus, the start of the fourth phase corresponds to the end of the third phase. Throughout the fourth phase 308, the controller 108 is configured to heat the heater track 114 toward a fourth target temperature of 190 degrees Celsius, again using thermostatic control. 190 degrees Celsius is represented by line 309 in FIG. 4. Because the fourth target temperature 309 is lower than the third target temperature 309, power is not initially provided to the heater assembly 102 because the heater track 114 has a temperature that exceeds the fourth target temperature 309. Once the heater track 114 has cooled to 190 degrees Celsius, the heater track 114 is maintained at that temperature by thermostatic control.

[0267] In Figure 4, the initial temperature of the heater assembly 102 is ambient or room temperature. Figure 5 shows the temperature of the heater assembly 102 when the same heating routine as Figure 4 is applied, but when the initial temperature of the heater assembly 102 is above ambient or room temperature. This may be the case, for example, when the current usage session occurs shortly after a previous usage session, such that the heater assembly 102 has not yet fully cooled down to ambient or room temperature.

[0268] In Figure 5, the decisions made by the controller 108 to proceed through each of the stages based on the timing and temperature signals are the same as in Figure 4. However, because the initial temperature is higher in Figure 5, the resulting temperature profile of the heater track 114 when applying the same heating routine as in Figure 4 is different.

[0269] Since the initial temperature is higher in FIG. 5 than in FIG. 4, the measured temperature of the heater track 114 is much closer to the first target temperature 303 by the end of the first phase. This means that during the second phase 304 (which is dynamic in duration), the heater track 114 reaches the second target temperature 305 more quickly than in FIG. 4, only 6 seconds after the start of the second phase, or 21 seconds after the start of the use session. Thus, in FIG. 5, the second phase 304 is shorter than in FIG. 4. The third phase 306 has a fixed duration between the third phase start and the third phase end, so that in both FIG. 4 and FIG. 5, the third phase ends 5 seconds after it starts. However, because the second phase is shorter in FIG. 5, the third phase ends 26 seconds after the start of the use session instead of 29 seconds as in FIG. 4.

[0270] The first, second and third phases 302, 304 and 306 correspond to pre-heating phases, in which the heater assembly 102 increases its temperature from an initial temperature at the beginning of a use session to a temperature at which substantial aerosol is generated. The total duration of the first, second and third phases 302, 304 and 306 thus corresponds to the total time that the user of the device has to wait until substantial aerosol is generated and the aerosol generating device is ready for the user to take a puff. It is desirable to have the pre-heating phase as short as possible. As shown by Figures 4 and 5, the advantage of the dynamic second phase 304 is that the early heating phase is short when the initial temperature of the heater track at t=0 is high.

[0271] A short pre-heating phase has the advantage that it consumes less battery power.

[0272] Releasing vapor from the aerosol-forming substrate not only requires increasing the temperature of the aerosol-forming substrate, but also requires the transfer of substantial energy from the heater assembly 102 to the aerosol-forming substrate 202 as latent heat of vaporization. Including a first and third stage with fixed duration in the early heating stage minimizes the time that power is supplied to the heater assembly 102 during the early heating stage, and therefore a minimum amount of energy is transferred to the aerosol-forming substrate 202. This minimum amount of energy takes into account the latent heat of vaporization.

[0273] The fourth stage 308 in Figures 4 and 5 represents heating after the pre-heat stage during the main stage of a use session, during which substantial aerosol is generated and during which the user can take one or more puffs on the aerosol-generating article. As mentioned above, Figures 4 and 5 show only the beginning of a use session. A use session is typically much longer than the portion shown in Figures 4 and 5, typically about four and a half minutes. In some embodiments, the fourth stage 308 continues throughout the entire main stage. However, in other embodiments, there may be any number of further successive stages that make up the main stage, each having a different target temperature to provide a desired experience for the user and to suit the type of aerosol-forming substrate being heated. For example, in some embodiments, the target temperature of one or more successive stages after the fourth stage may be increased to account for depletion of the aerosol-forming substrate, thus ensuring consistent aerosol generation throughout the use session.

[0274] 4 and 5, the first, second and third target temperatures 303, 305 and 307 are all 250 degrees Celsius. However, in other embodiments, different target temperatures may be selected.

[0275] Additionally, the fixed durations of the first and third phases 302 and 306, and the maximum duration of the second phase 304 may be different. In one embodiment, the fixed duration of the first phase 302 is 8 seconds, the maximum duration of the second phase 304 is 6 seconds, and the third phase 306 is 20 seconds.

[0276] 6 shows a graph 400 illustrating a second embodiment of a portion of a heating routine implemented by the controller 108, whereby the controller 108 controls heating based on temperature and timing signals. The X-axis of the graph 400 represents time in seconds. Zero (t=0) on the X-axis represents the start of a usage session of the aerosol generating device 100. The Y-axis of the graph 400 represents temperature. In particular, the Y-axis of the graph 400 represents the temperature of the heating track 114 as measured by the temperature sensor 104.

[0277] The heating routine portion of FIG. 6 includes four successive steps.

[0278] The first phase 402 is dynamic in length. If at any time during the first phase 402 the controller 108 determines that the temperature of the heater track 114, as measured by the temperature sensor 104, exceeds a first target temperature of 190 degrees Celsius, the controller 108 is configured to proceed to a second phase 404. The first target temperature is represented by line 403 in FIG. 6. However, the first phase 402 has a maximum length of 10 seconds, so that the second phase ends no later than 10 seconds after the start of the second phase. If the 10 seconds of the first phase 402 elapse before the controller 108 determines that the temperature of the heater track 114 has exceeded the first target temperature 403, the controller 108 proceeds to the second phase 404 regardless. In FIG. 6, the controller 108 determined that the heater track 114 reached the first target temperature 403 shortly before the maximum length of the first phase 402. Thus, the end of the first phase occurs approximately 9 seconds after the end of the first phase, rather than a maximum of 10 seconds.

[0279] Throughout the second phase 304, the controller is configured to heat the heater track 114 toward a second target temperature of 250 degrees Celsius, represented by line 405 in FIG. 6. The controller is configured to change the temperature of the heater track 114 at a constant rate of 3 degrees Celsius per second due to heating. In particular, the controller 108 is configured to repeatedly measure the temperature of the heater track 114 based on signals received from the temperature sensor 104. Based on these signals, the controller 108 is configured to determine a rate of change of the heater track temperature and to control the supply of power to the heater assembly 102 to maintain the rate of change of the heater track temperature at a constant value of 3 degrees Celsius per second. If the determined rate of change of the heater track temperature is less than 3 degrees Celsius per second, the controller is configured to increase the power supplied to the heater assembly 102. If the determined rate of change of the heater track temperature is greater than 3 degrees Celsius, the controller is configured to decrease the power supplied to the heater assembly 102.

[0280] When the controller 108 determines that the measured temperature of the heater track 114 has reached the second target temperature 405, the controller 108 is configured to transition to a third phase 406. In other words, the end of the second phase is when the controller 108 determines that the measured temperature of the heater track 114 has reached the second target temperature 405.

[0281] The third phase 406 is of fixed duration. The third phase end is 5 seconds after the third phase start, which corresponds to the second phase end. In the third phase 406, the controller is configured to maintain the measured temperature of the heater track 114 at a third target temperature, also of 250 degrees, as represented by line 407 in FIG. 6.

[0282] Upon completion of the third stage 406, the controller 108 is configured to transition to a fourth stage 408 in which the controller is configured to maintain the heater track 114 at a temperature of 190 degrees Celsius, as represented by line 409 in FIG. 6.

[0283] In the second embodiment, the first, second and third stages 402, 404 and 406 may be referred to as early heating stages.

[0284] Controlling the heating so that the rate of change of the temperature measured by the temperature sensor 104 is constant takes into account any discrepancy between the actual temperature of the heater track 114 and the temperature measured by the temperature sensor 104. The temperature measured by the temperature sensor 104 will typically be lower than the actual temperature of the heater track 114, especially while the temperature of the heater track 114 is increasing. This is because it takes time for energy from the heater track 114 to be transferred to the temperature sensor 104 so that the two temperatures equilibrate. Maintaining a constant rate of change of the measured temperature at 3 degrees Celsius per second avoids heating the temperature of the heater track 114 substantially beyond the second target temperature.

[0285] The heater assembly 102 is designed to operate up to approximately 280 degrees Celsius. If the actual temperature of the heater assembly, and particularly the heater track 114, substantially exceeds 280 degrees Celsius, overheating may occur. Avoiding overheating of the heater track 114 prevents damage to the heater assembly 102.

[0286] A third stage 406 is provided in which the heater track 114 is maintained at a third target temperature 407 to allow additional time for the actual temperature of the heater assembly 102 to equilibrate with the measured temperature.

[0287] 7 shows a graph 500 representing a third embodiment of a portion of a heating routine implemented by the controller 108, whereby the controller 108 controls the heating based on temperature and timing signals. The third embodiment combines features of both the first and second embodiments. The X-axis of the graph 500 represents time in seconds. Zero (t=0) on the X-axis represents the start of a usage session of the aerosol generating device 100. The Y-axis of the graph 500 represents temperature. In particular, the Y-axis of the graph 500 represents the temperature of the heating track 114 as measured by the temperature sensor 104.

[0288] The heating routine portion of FIG. 7 includes six consecutive stages. The first stage 502 and the second stage 504 of the third embodiment are similar to the first stage 202 and the second stage 204 of the first embodiment. The target temperature of the first stage 502 and the second stage 504 is 190 degrees Celsius, as represented by lines 503 and 505 in FIG. 7, rather than 250 degrees Celsius as in the first embodiment. Furthermore, the fixed duration of the first stage 502 of the third embodiment is shorter than that of the first embodiment. The fixed duration of the first stage 502 is 5 seconds. Thus, the first stage 502 starts at 0 seconds, and the first stage ends 5 seconds after the first stage starts. During the first stage 502, the controller is configured to reach a first target temperature 503 of 190 degrees Celsius using a thermostatic control.

[0289] Once the controller 108 determines that five seconds of the first phase 502 have elapsed, it is configured to transition to the second phase 504. Thus, the start of the second phase corresponds to the end of the first phase.

[0290] The second phase 504 is dynamic in length. If at any time during the second phase 504 the controller 108 determines that the temperature of the heater track 114, as measured by the temperature sensor 104, exceeds the second target temperature 505, the controller 108 is configured to proceed to the third phase 506. However, the second phase 504 has a maximum length of 10 seconds, so that the second phase ends no later than 10 seconds after the start of the second phase or 15 seconds after the start of the usage session. If the 10 seconds of the second phase elapse before the controller 108 determines that the temperature of the heater track 114 exceeds the second target temperature 505, the controller 108 transitions to the third phase 506 regardless. In FIG. 7, the controller 108 determined that the heater track 114 reached the second target temperature 505 3 seconds after the start of the second phase, i.e., before the maximum length of the second phase. Thus, the second phase ends approximately 3 seconds after the first phase ends, rather than up to 10. Upon completion of the second phase 504, the controller 108 is configured to proceed to the third phase 506.

[0291] In the third phase 506, the controller 108 is configured to implement the type of control described in relation to the second phase 304 of the second embodiment. In particular, throughout the third phase 506, the controller 108 is configured to heat the heater track 114 towards a third target temperature of 250 degrees Celsius, represented by line 507 in FIG. 7, while maintaining a constant rate of change of the temperature of the heater track 114. As described in relation to FIG. 6, the controller 108 is configured to repeatedly measure the temperature of the heater track 114 based on signals received from the temperature sensor 104. Based on these signals, the controller 108 is configured to determine a rate of change of the temperature of the heater track 114 and to control the supply of power to the heater assembly 102 to maintain the rate of change of the temperature of the heater track 114 at a constant value of 3 degrees Celsius per second. If the determined rate of change of the temperature of the heater track 114 is lower than 3 degrees Celsius per second, the controller 108 is configured to increase the power supplied to the heater assembly 102. If the determined rate of change of the temperature of the heater track 114 is greater than 3 degrees Celsius, the controller 108 is configured to reduce the power supplied to the heater assembly 102 .

[0292] When the controller 108 determines that the measured temperature of the heater track 114 has reached the third target temperature 507 of 250 degrees Celsius, the controller 108 is configured to transition to a fourth phase 508. In other words, the end of the third phase is when the controller 108 determines that the measured temperature of the heater track 114 has reached the third target temperature 507.

[0293] The fourth phase 508 is of fixed duration. The fourth phase end is 5 seconds after the fourth phase start, which corresponds to the third phase end. In the fourth phase 508, the controller 108 is configured to maintain the measured temperature of the heater track 114 at a fourth target temperature, also represented by line 509 in FIG. 7 at 250 degrees.

[0294] At the end of the fourth phase 508, the controller 108 is configured to transition to a fifth phase 510 in which the controller 108 is configured to maintain the heater track 114 at a temperature of 190 degrees Celsius. The fifth phase start corresponds to the fourth phase end. The fifth phase 510 is of fixed duration. The fifth phase end is 40 seconds after the fifth phase start. In the fifth phase 510, the controller is configured to maintain the measured temperature of the heater track 114 at a fifth target temperature of 190 degrees, represented by line 511 in FIG. 7.

[0295] At the end of the fifth phase 510, the controller 108 is configured to transition to a sixth phase 512 in which the controller 108 is configured to maintain the heater track 114 at a target temperature of 240 degrees Celsius, represented by line 513 in Figure 7. The start of the sixth phase corresponds to the end of the fifth phase. In the sixth phase 510, the controller 108 is configured to maintain the measured temperature of the heater track 114 at the sixth target temperature of 240 degrees.

[0296] In the third embodiment, the first, second, third and fourth stages 502, 504, 506 and 508 may be referred to as preheat stages.

[0297] 8-12 show a fourth embodiment of a heating routine implemented by controller 108 whereby controller 108 is configured to limit the average power supplied by power supply 106 so as not to exceed a threshold average power and so that the amount of energy supplied to the heater assembly does not exceed the threshold energy.

[0298] Step 802 of Figure 8 is divided into three sub-steps, steps 802a to 802c. Throughout step 802, the controller is configured to perform each of steps 802a to 802c every millisecond over a period of 50 milliseconds.

[0299] In step 802a, the controller 108 is configured to measure the instantaneous power supplied to the heater track 114. The controller 108 can determine the instantaneous power supplied to the heater track 114 based on measurements of the voltage and current supplied to the heater track 114 by the power supply 106. These measurements are made by a voltmeter and an ammeter, not shown in the figure. The instantaneous power is then determined by multiplying the voltage by the current. The power determined in step 802a is the instantaneous power.

[0300] At step 802 b , the controller 108 is configured to determine the cumulative energy delivered to the heater track 114 since the beginning of the 50 millisecond period introduced at step 802 .

[0301] To determine the cumulative energy, the controller 108 is configured to first determine the energy delivered to the heater track throughout the previous millisecond. This is possible because the amount of energy delivered during a particular time interval is equal to the instantaneous power multiplied by the time interval. Therefore, the energy delivered to the heater track in the last millisecond is determined by multiplying the instantaneous power determined in step 802a by 0.001 (i.e., milliseconds). This calculation assumes that the instantaneous power determined in step 802a is constant for the previous millisecond.

[0302] After determining the energy delivered to the heater track through the previous millisecond, the controller is configured to determine the cumulative energy by continuously maintaining a sum of the amount of energy determined to have been delivered to the heater track each millisecond.

[0303] In step 802c, the controller is configured to limit the power supplied to the heater track 114 if the accumulated energy is equal to or greater than a threshold energy. Limiting the power supplied to the heater track 114 means turning off power to the heater track. The threshold energy is a value stored in the memory of the controller. In this embodiment, the threshold energy is 540 millijoules.

[0304] Since energy and power are related, limiting the power delivered to the heater track when the accumulated energy is equal to or greater than the threshold energy is equivalent to limiting the power to a threshold average power. The threshold average power corresponds to the power that the threshold energy would be delivered during a 50 millisecond period. In other words, since the threshold energy is 540 millijoules and the period is 50 milliseconds, the threshold average power is 540 millijoules divided by 50 milliseconds, which is 10.8 watts. The effect of stopping or limiting the power when the accumulated energy by the end of the 50 millisecond period is equal to or greater than the threshold energy is that the average power delivered throughout the 50 millisecond period does not exceed the threshold average power.

[0305] Step 804 is to repeat step 802 for an additional 50 millisecond period. In this embodiment, step 802 is repeated for consecutive 50 millisecond periods throughout an entire use session of the aerosol generating device 100.

[0306] FIG. 9 is a graph 600 showing the accumulated energy delivered to the heater track 114 during the 50 millisecond period of step 802. The X-axis represents time in seconds. The Y-axis represents the accumulated energy delivered to the heater track 114. FIG. 9 shows that for approximately the first 24 milliseconds, the accumulated energy increases linearly. This indicates that for approximately the first 24 milliseconds, the instantaneous power delivered to the heater track 114, determined each millisecond according to step 802a, was constant. However, by 25 milliseconds, the accumulated energy has reached the threshold energy, stored in the controller 108 and represented by the dotted line 602 in FIG. 9. Thus, for the remaining 50 millisecond period, power is no longer delivered to the heater track. This means that the accumulated energy delivered to the heater track 114 stops increasing after approximately 25 milliseconds and therefore does not exceed the threshold energy.

[0307] FIG. 10 is another graph 700 showing power supplied to the heater track 114 instead of energy as in FIG. 9. FIG. 10 shows two successive 50 millisecond periods. The X-axis of FIG. 10 represents time in seconds. The Y-axis represents power supplied to the heater track 114. In relation to FIG. 9, it was explained that the power supplied to the heater track 114 during the 50 millisecond period is constant until about 24 milliseconds, after which power ceases to be supplied for the remaining 50 millisecond period. This is also shown in FIG. 10, which shows the power initially as a constant non-zero value, then zero after about 24 milliseconds. The same pattern is repeated for a second 50 millisecond period.

[0308] By limiting the power when the accumulated energy equals the threshold energy, the average power delivered during any 50 millisecond period is equal to the threshold average power, as described above. The average power is represented by line 702 in FIG. 10. The threshold average power is selected as a power high enough to provide fast heating, while being limited to take into account the variability of the maximum amount of power delivered by the power source 106 at any given time. For example, the maximum power that can be delivered by the power source 106 at any given time depends on the state of charge of the battery. When the battery is fully charged, it can deliver a higher maximum power than when it is depleted. This is because the voltage of the battery decreases as the battery depletes.

[0309] Because the maximum available power decreases as the power source depletes, the user experience during a use session at different states of charge of the power source would be inconsistent without the power limiting described above. For example, in a later use session, the time it takes for the heater track 114 to heat up to operating temperature may be much longer, or the amount of aerosol generated during a use session may be lower. By limiting the power to a predetermined power, the average power supplied during any 50 millisecond period can be delivered at most states of charge of the power source 106, meaning that the aerosol generating device is more stable.

[0310] The threshold average power is 10.8 watts in this embodiment, selected as a good balance between what the heater track 114 can get from the power source 106 at various states of charge, while still being high enough to raise the temperature quickly.

[0311] The change in power limit control to account for the different charge states of the power source 106 is more clearly shown by comparing FIG. 10 with FIG. 11. Unlike FIG. 10, where the power source 106 is fully charged, the power source 106 in FIG. 11 is somewhat depleted. Thus, in FIG. 11, the maximum power that can be supplied by the power source 106 is less than in FIG. 10. Thus, the instantaneous power initially supplied in each of the 50 millisecond periods in FIG. 11 is lower than in FIG. 10. This means that the cumulative energy takes longer to reach maximum energy in FIG. 11 because the lower the power, the less energy is supplied per millisecond. Thus, in FIG. 11, power is supplied to the heater track 114 for longer than in FIG. 10 (about 40 milliseconds instead of about 25 milliseconds). However, in both FIG. 10 and FIG. 11, during each 50 millisecond period, 540 millijoules of energy are supplied to the heater track, which corresponds to an average power of 10.8 watts over the 50 millisecond period.

[0312] The amount of power that drops as the power supply depletes is exaggerated in Figures 10 and 11. If the energy delivered in each of the 50 millisecond time intervals in Figures 10 and 11 is 540 millijoules, the maximum power in Figure 10 drops from about 21.6 watts in Figure 11 to about 13.4 watts. In reality, the power drop is likely to be on the order of a few watts.

[0313] The energy and power limited heating routine of the fourth embodiment may be applied to the first, second and third embodiments described above and may be applied to all or part of the use session of those embodiments. For example, in the first phase 202 of Figure 4, heating the heater track towards a first target temperature of 250 degrees involves supplying power to the heater track 114 until the measured temperature of the heater track 114 reaches the first target temperature. The power supplied in this phase is an average power of 10.8 watts.

[0314] Of course, for periods of about 50 milliseconds, the average power may be less than 10.8 watts. This may be during periods when no power is applied to the heater track 114, for example, because the heater track 114 is already hotter than the target temperature, or because lower power is being applied to ensure that the heater track 114 has a constant rate of temperature change. In these cases, the routine of FIG. 8 still applies, but step 802c is not reached.

[0315] Figure 12 shows a graph 900 representing a heating profile applied to the aerosol-forming substrate 202 of the aerosol-generating article 200 during a use session by the aerosol-generating device 100 according to the embodiment of Figure 1. The y-axis of the graph represents temperature and the x-axis of the graph represents time in seconds. This heating profile may result in excellent generation of aerosol when used with an external heating device such as that disclosed in the embodiment of Figure 1. The use session lasts for 265 seconds from the start of the use session to the end of the use session. The heating profile includes six successive stages.

[0316] The duration of each step may be controlled based on a combination of signals, such as a temperature signal and a time signal. For example, the duration of each of the successive steps may be controlled as described above in connection with the embodiment of Figures 4-7.

[0317] The first phase 902 lasts from the start of the usage session (t=0 seconds). The first phase 902 is dynamic in length. If at any time during the first phase 902 the controller 108 determines that the temperature of the heater track 114 measured by the temperature sensor 104 exceeds a first target temperature of 210 degrees Celsius, the controller 108 is configured to proceed to a second phase 904. The first target temperature is represented by line 903 in FIG. 12. However, the first phase 902 has a maximum length of 10 seconds, so that the end of the first phase is no later than 10 seconds after the start of the first phase. If the 10 seconds of the first phase 402 elapse before the controller 108 determines that the temperature of the heater track 114 exceeds the first target temperature 903, the controller 108 proceeds to the second phase 904 regardless. 12, the controller 108 has determined that the heater track 114 has reached the first target temperature 903 shortly before the maximum length of the first phase 902. Thus, the end of the first phase is approximately 8 seconds after the start of the first phase, rather than the maximum of 10 seconds.

[0318] Throughout the second phase 904, the controller is configured to heat the heater track 114 towards a second target temperature of 255 degrees Celsius, represented by line 905 in Figure 12. Once the controller 108 determines that the measured temperature of the heater track 114 has reached the second target temperature 905, the controller 108 is configured to transition to a third phase 906. In other words, the end of the second phase is when the controller 108 determines that the measured temperature of the heater track 114 has reached the second target temperature 905. In the graph of Figure 12, this occurs 20 seconds after the start of the use session.

[0319] The third phase 906 is of fixed duration. The third phase end is 10 seconds after the third phase start, and the third phase start corresponds to the second phase end. In the third phase 906, the controller is configured to maintain the measured temperature of the heater track 114 at a third target temperature, also of 255 degrees, as represented by line 907 in FIG. 12.

[0320] The first, second and third phases 902, 904 and 906 may be referred to as an early heating phase, or a first period, of a use session.

[0321] At the end of the third phase 906, the controller 108 is configured to transition to a fourth phase 908 in which the controller is configured to allow the heater track 114 to reach a fourth target temperature of 195 degrees Celsius, as represented by line 909 in Figure 12. The start of the fourth phase corresponds to the end of the third phase. The fourth phase ends when the controller 108 determines that the measured temperature of the heater track 114 has reached the fourth target temperature 909. In the graph of Figure 12, this occurs 75 seconds after the start of the use session.

[0322] The fifth phase 910 is of fixed duration. The end of the fifth phase is 30 seconds after the start of the fifth phase. In the fifth phase 910, the controller is configured to maintain the measured temperature of the heater track 114 at a fifth target temperature of 195 degrees, represented by line 911 in FIG. 12.

[0323] The fourth and fifth stages may be referred to as a second period of the use session.

[0324] At the end of the fifth phase 910, the controller 108 is configured to transition to a sixth phase 912, where the controller 108 is configured to maintain the heater track 114 at a sixth target temperature of 218 degrees Celsius, represented by line 913 in Figure 12. The start of the sixth phase corresponds to the end of the fifth phase. The sixth phase ends 165 seconds after the start of the use session.

[0325] At the end of the sixth phase 912, the controller 108 is configured to transition to a seventh phase 914, where the controller 108 is configured to maintain the heater track 114 at a seventh target temperature of 225 degrees Celsius, represented by line 915 in Figure 12. The start of the seventh phase corresponds to the end of the sixth phase. The seventh phase ends 200 seconds after the start of the use session.

[0326] At the end of the seventh phase 914, the controller 108 is configured to transition to an eighth phase 916, where the controller 108 is configured to maintain the heater track 114 at an eighth target temperature of 250 degrees Celsius, represented by line 917 in FIG. 12. The start of the eighth phase corresponds to the end of the seventh phase. The eighth phase ends when the eighth target temperature is reached. In FIG. 12, the eighth phase ends 250 seconds after the start of the use session.

[0327] At the end of the eighth phase 916, the controller 108 is configured to transition to a ninth phase 918, in which the controller 108 is configured to maintain the heater track 114 at a ninth target temperature of 250 degrees Celsius, represented by line 919 in Figure 12. The start of the ninth phase corresponds to the end of the eighth phase. The ninth phase ends 265 seconds after the start of the use session.

[0328] The sixth, seventh, eighth, and ninth stages may be referred to as a third period of the use session.

[0329] At the end of the ninth step, the use session ends and the heater is turned off.

[0330] Figure 13 shows a graph 1000 illustrating a further specific example of a heating profile applied by an aerosol-generating device 100 according to the embodiment of Figure 1 to the aerosol-forming substrate 202 of an aerosol-generating article 200 during a use session. As in Figure 12, the y-axis of the graph represents temperature and the x-axis of the graph represents time in seconds. This heating profile may result in excellent generation of aerosol when used with an external heating device such as that disclosed in the embodiment of Figure 1. The use session lasts for 273 seconds from the start of the use session to the end of the use session. The heating profile includes seven successive steps of fixed length.

[0331] A first phase 1002 lasts from the start of the usage session (t=0 seconds). The first target temperature is represented by line 1005 in FIG. 13. The first target temperature is 235 degrees Celsius and the first phase has a length of 28 seconds. During the first phase, power is supplied at 6.5 watts until the target temperature is achieved, after which power is supplied to maintain the temperature at the first target temperature until the end of the first phase.

[0332] The second phase 1006 lasts from the end of the first phase (28 seconds into the use session) to 35 seconds into the use session. During the second phase, the temperature increases linearly from 235 degrees Celsius to a second target temperature 1007 of 240 degrees Celsius. The first and second phases may be described as an initial period during which the temperature increases from an initial temperature (i.e., ambient temperature) to the first temperature (240 degrees Celsius).

[0333] The third phase 1010 is of fixed duration. The third phase lasts from the end of the second phase (35 seconds from the start of the use session) to 103 seconds from the start of the use session. During the third phase, the temperature is controlled to decrease linearly from 240 degrees Celsius to a third target temperature 1009 of 200 degrees Celsius. The third phase may be described as a second phase in which the temperature of the heating element decreases to a second temperature (200 degrees Celsius) below the first temperature.

[0334] Upon completion of the third phase 1010, the controller 108 is configured to transition to a fourth phase 1012, in which the controller is configured to allow the heater track 114 to reach a fourth target temperature 1013 of 218 degrees Celsius. The fourth phase lasts from the end of the third phase (103 seconds from the start of the use session) to 165 seconds from the start of the use session.

[0335] Upon completion of the fourth phase 1012, the controller 108 is configured to transition to a fifth phase 1014, where the controller is configured to allow the heater track 114 to reach a fifth target temperature 1015 of 225 degrees Celsius. The fifth phase lasts from the end of the fourth phase (165 seconds from the start of the use session) to 208 seconds from the start of the use session.

[0336] At the end of the fifth phase 1014, the controller 108 is configured to transition to a sixth phase 1016, where the controller is configured to allow the heater track 114 to reach a sixth target temperature 1017 of 250 degrees Celsius. The sixth phase lasts from the end of the fourth phase (208 seconds from the start of the use session) to 258 seconds from the start of the use session. The fourth, fifth, and sixth phases may be described as a third period during which the temperature of the heating element increases to a third temperature (250 degrees Celsius) that is higher than the second temperature.

[0337] Upon completion of the sixth phase 1016, the controller 108 is configured to transition to a seventh phase 1018 in which the controller is configured to maintain the heater track 114 at a target temperature 1019 of 250 degrees Celsius. The sixth phase lasts from the end of the fifth phase (258 seconds from the start of the use session) until 273 seconds from the start of the use session, at which point the heater is turned off and the use session ends.

[0338] The power supplied during the first period (i.e., the first and second stages) may be 6.5 W, and the power supplied during the second and third periods (i.e., the third, fourth, fifth, sixth, and seventh stages) may be reduced to 5.5 W.

[0339] For the purposes of this specification and the appended claims, unless otherwise indicated, all numbers expressing amounts, quantities, percentages, and the like should be understood in all cases as modified by the term "about." Also, all ranges include the maximum and minimum points disclosed, and include any intermediate ranges therein, which may or may not be specifically recited herein. Thus, in this context, the number A is understood as A±10% of A. Within this context, the number A may be considered to include numerical values ​​that are within the general standard error for the measurement of the property that the number A modifies. The number A may deviate by the percentages recited above, in some cases as used in the appended claims, provided that the amount by which A deviates does not materially affect the basic and novel property(ies) of the claimed invention. Also, all ranges include the maximum and minimum points disclosed, and include any intermediate ranges therein, which may or may not be specifically recited herein.

Claims

1. 1. A method for controlling aerosol generation in an aerosol generating device, the device comprising: a heating chamber configured to at least partially receive an aerosol-generating article including an aerosol-forming substrate; and a heater including at least one heating element configured to externally heat the aerosol-forming substrate; a power source for providing power to the heating element; power is provided during a first period of time such that the temperature of the heating element rises from an initial temperature to a first temperature, power is provided during a second period of time such that the temperature of the heating element falls to a second temperature below the first temperature, and power is provided during a third period of time such that the temperature of the heating element rises to a third temperature higher than the second temperature, the first temperature being between 230°C and 270°C; the aerosol generating device is configured to generate an aerosol during a use session; and the method Dividing at least a portion of a usage session into n consecutive time intervals; and 10. A method comprising: controlling the power provided to the heating element to limit the power supplied to the heater assembly during any or each of n consecutive time intervals so as not to exceed a threshold energy for that time interval.

2. 2. The method of controlling aerosol generation of claim 1, wherein the first temperature is a temperature between 235°C and 245°C or between 245°C and 265°C.

3. 3. The method for controlling aerosol generation according to any one of claims 1 to 2, wherein the second temperature is a temperature between 140°C and 220°C.

4. 2. The method of controlling aerosol generation of claim 1, wherein the third temperature is a temperature between 230°C and 270°C.

5. 2. The method of controlling aerosol generation according to claim 1, wherein the first period has a duration of from 20 seconds to 40 seconds, such as from 25 seconds to 35 seconds, for example about 30 seconds.

6. 2. The method of controlling aerosol generation according to claim 1, wherein the second period has a duration of from 40 seconds to 100 seconds, such as from 50 seconds to 90 seconds, such as from 60 seconds to 80 seconds, such as about 70 seconds.

7. 2. The method of controlling aerosol generation according to claim 1, wherein the third period has a duration of from 40 seconds to 100 seconds, such as from 50 seconds to 90 seconds, such as from 60 seconds to 80 seconds, such as about 70 seconds.

8. 2. The method of controlling aerosol generation according to claim 1, wherein the aerosol generating device is configured to generate the aerosol during a use session, the use session having a use session start and a use session end.

9. 2. The method of controlling aerosol generation of claim 1, wherein the temperature of the heating element is at the initial temperature at the start of the use session, and the end of the third period is the end of the use session.

10. A method for controlling aerosol generation as described in claim 8 or 9, wherein the step of controlling the power provided to the heating element is performed to maintain the temperature of the heating element within a desired temperature range during the second and third periods of the use session.

11. 11. The method of controlling aerosol generation of claim 10, wherein the desired temperature range has a lower limit of 140°C to 220°C and an upper limit of 230°C to 270°C.

12. The method of claim 1 , wherein the first period of time ends when the heating element reaches the first temperature.

13. The method of claim 1 , wherein the duration of the second period is determined based on a total amount of power provided to a heating element during the second period.

14. 10. The method of claim 1, further comprising detecting a user puff at the aerosol generating device, wherein the first, second, or third period ends after detecting a predetermined number of user puffs.

15. 1. An electrically operated aerosol generating device configured to generate an aerosol during a session of use, comprising: a heating chamber configured to at least partially receive an aerosol-generating article comprising an aerosol-forming substrate; a heater including at least one heating element configured to externally heat the aerosol-forming substrate; a power source for providing power to the heating element; an electrical circuit for controlling the supply of power from the power source to the at least one heating element, the electrical circuit comprising: during a first period of time, power is provided to increase the temperature of the heating element from an initial temperature to a first temperature, during a second period of time power is provided to decrease the temperature of the heating element to a second temperature below the first temperature, and during a third period of time power is provided to increase the temperature of the heating element to a third temperature above the second temperature, the first temperature being between 230°C and 270°C; Dividing at least a portion of a usage session into n consecutive time intervals; and An electrically operated aerosol generating device arranged to control the power provided to the heating element so as to limit the power supplied to the heater assembly during any or each of n consecutive time intervals so as not to exceed a threshold energy for that time interval.

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