An aerosol generating device, and a method of heating an aerosol generating article

Abstract

An aerosol generating device (10) includes a heating chamber (18) adapted to receive an aerosol generating article (100) including aerosol generating material (102). A heater assembly (36) includes a first heater to heat an area of the aerosol generating article (100) and a second heater to heat at least part of the same area of the aerosol generating article (100). A controller controls operation of the first heater according to a first duty cycle and operation of the second heater according to a second duty cycle. The first heater has a first heat distribution pattern with at least one region that is cooler than at least one other region. The second heater has a second heat distribution pattern with at least one region that is hotter than at least one other region. The at least one hotter region of the second heat distribution pattern is aligned with the at least one cooler region of the first heat distribution pattern.

Description

[0001] AN AEROSOL GENERATING DEVICE, AND A METHOD OF HEATING AN AEROSOL GENERATING ARTICLE

[0002] Technical Field

[0003] The present disclosure relates generally to an aerosol generating device that includes a heating chamber adapted to receive an aerosol generating article for generating an aerosol for inhalation by a user. The present disclosure is particularly applicable to a portable (hand-held) aerosol generating device.

[0004] The present disclosure also relates to a method of heating an aerosol generating article comprising aerosol generating material.

[0005] Technical Background

[0006] Devices which heat, rather than bum, an aerosol generating material to produce an aerosol for inhalation have become popular with consumers in recent years. A commonly available reduced-risk or modified- risk device is the heated material aerosol generating device, or so-called heat-not-bum device. Devices of this type generate an aerosol or vapour by heating an aerosol generating material to a temperature typically in the range 150°C to 300°C, and in some cases as high as 350°C. This temperature range is quite low compared to an ordinary cigarette. Heating the aerosol generating material to a temperature within this range, without burning or combusting the aerosol generating material, generates a vapour which typically cools and condenses to form an aerosol for inhalation by a user of the device.

[0007] Such devices may use one of a number of different approaches to provide heat to the aerosol generating material. One approach is to heat the aerosol generating material using a heater such as a resistive heater. The heater will often have an uneven heat distribution pattern, which means that the aerosol generating material is not heated evenly - i.e., where some areas are heated more or less than others. For example, Figure 1 shows a flat heater 200 having a serpentine construction. The heater 200 is formed as an electrically conductive heating element with a first end part 202, a second end part 204, and an intermediate or central part 206. The heat distribution pattern associated with the flat heater 200 is shown in Figure 2 and it may be seen that the coldest regions (which are shown with the lowest density of shading) are at the first and second end parts 202, 204 and the hottest region (which is shown with the highest density of shading) is at the intermediate or central part 206. Figure 3 shows a cylindrical heater 300 having a serpentine construction. The heater 300 is formed as an electrically conductive heating element with a first end part 302, a second end part 304, and an intermediate part 306. The heat distribution pattern associated with the cylindrical heater 300 is shown in Figure 4 and it may be seen that the coldest region (which is shown with the lowest density of shading) is at the part where the first and second end parts 302, 304 meet and the hottest region (which is shown with the highest density of shading) is at the intermediate part 306. The hottest region is diametrically opposite the coldest region. Aerosol generating material that is adjacent the hottest region of the heater may be heated more than the

[0008] P51844WO-6722 aerosol generating material that is adjacent the coldest region of the heater. The uneven heating of the aerosol generating material may be more pronounced during some phases of the vaping session than others, e.g., during pre-heating where the aerosol generating article is heated rapidly from ambient temperature to a target temperature, and this may result in some areas of the aerosol generating material being heated too much. Other areas of the aerosol generating material may not be heated enough, which may have a negative effect on aerosol generation. Embodiments of the present disclosure seek to provide more even heating of the aerosol generating material by a heater assembly of an aerosol generating device. This may result in more accurate control of the heating of the aerosol generating material and optimise the characteristics of the generated aerosol.

[0009] Summary of the Disclosure

[0010] According to a first aspect of the present disclosure, there is provided an aerosol generating device comprising: a heating chamber adapted to receive an aerosol generating article in use; a heater assembly comprising: a first (or main or primary) heater adapted to heat an area of the aerosol generating article when the aerosol generating article is received in the heating chamber, and a second (or secondary) heater adapted to heat at least part of the same area of the aerosol generating article when the aerosol generating article is received in the heating chamber; and a controller adapted to control operation of the first heater according to a first duty cycle and to control operation of the second heater according to a second duty cycle; wherein the first heater has an associated first heat distribution pattern with at least one region that is cooler than at least one other region; and wherein the second heater has an associated second heat distribution pattern with at least one region that is hotter than at least one other region, and wherein the at least one hotter region of the second heat distribution pattern is substantially aligned with the at least one cooler region of the first heat distribution pattern. In other words, the heat generated by the second heater at least partially compensates for reduced heat generated by the first heater at the cooler region(s) to provide more even or consistent heating of the area of the aerosol generating article when the first and second heaters are operated at the same time. In some arrangements, two or more second heaters may be provided, where each second heater is positioned to compensate for reduced heating at a respective cooler region of the first heat distribution pattern. By beneficially combining the first and second heat distribution patterns associated with the first and second heaters, the heater assembly provides more even heating than a single heater.

[0011] As used herein, the term “duty cycle” means the proportion of time during each cycle period when the heater is turned on. Each cycle period is the total duration of an on and off state, i.e., the total time during which the heater is turned on and off by the controller in a single cycle. The pulse width is the time when

[0012] P51844WO-6722 the heater is turned on, i.e., the duration of the on state. The duty cycle D may be expressed as a percentage:

[0013] PW D = - X 100%

[0014] P where PW is the pulse width and P is the cycle period. Any suitable cycle period may be used (e.g., 100 ms).

[0015] It will be understood that a duty cycle of 90% means that the heater is turned on for 90% of each cycle period and turned off for the remaining 10% of each cycle period, for example. The controller may adjust the temperature of the first and second heaters, and hence the amount of heat they generate, by controlling or adjusting the duty cycle, i.e., by increasing or decreasing the pulse width. Such control may therefore also be described in terms of pulse width modulation (PWM) control where the pulse width is adjusted (or “modulated”) to control the amount of time for which the respective heater is turned on. For example, increasing the pulse width, and hence using a higher duty cycle, means that a heater is in the on state for a greater proportion of each cycle period and this means that more heat will be generated by the heater, and vice versa.

[0016] The first and second duty cycles may be adjusted independently by the controller to independently control the temperature and the heat generated by the first and second heaters. This may allow for more flexible control when heating the aerosol generating article. If two or more second heaters are provided, each having its own duty cycle, the duty cycles may be adjusted independently or in tandem by the controller - i.e., where in the latter case each second heater has the same duty cycle.

[0017] At least part of the same area of the aerosol generating article may be heated by both the first and second heaters during a vaping session, i.e., when the aerosol generating device is used to heat the aerosol generating article that is received in the heating chamber to generate an aerosol that is inhaled by the user. This may provide more even and consistent heating of the aerosol generating article.

[0018] Preferably, the at least one cooler region is the coldest region of the first heat distribution pattern, and the at least one hotter region is the hottest region of the second heat distribution pattern. This may provide a more even or consistent heating of the aerosol generating article.

[0019] The first heat distribution pattern will have at least one region that is hotter than at least one other region and the second heat distribution pattern will have at least one region that is cooler than at least one other region. The at least one cooler region of the second heat distribution pattern may be substantially aligned with the at least one hotter region of the first heat distribution pattern. The at least one hotter region of the first heat distribution pattern may be the hottest region of the first heat distribution pattern, and the at

[0020] P51844WO-6722 least one cooler region of the second heat distribution pattern may be the coldest region of the second heat distribution pattern.

[0021] The first and second heaters may be resistive heaters, i.e., they may be designed to heat the aerosol generating article by Joule heating when an electric current is supplied to the first and second heaters, e.g., from an energy storage device such as a rechargeable battery or capacitor, or other suitable power source. The hotter and cooler regions in the respective heat distribution pattern may be caused by temperature differences across the heater, which in turn may be the result of differences in the electrical resistance within the heater or heating element, and also by the shape or configuration of the heater. For example, regions of the heater that have a higher temperature or where more heat is generated because of the shape or configuration of the heater, will result in a hotter region of the heat distribution pattern and vice versa. The first and second heaters may be flat or tubular heaters. For example, the first and second heaters may be flat heaters that are arranged adjacent the heating chamber, or they may be tubular heaters that are arranged around the heating chamber - i.e., where each heater extends substantially around the circumference of the heating chamber. The heating chamber may have any suitable crosssection, e.g., circular, elliptical or polygonal etc. and may be adapted to receive a suitable aerosol generating article that comprises aerosol generating material as described in more detail below.

[0022] The first and second heaters may be at least partially overlapping - i.e., at least part of the first heater may be overlapped by at least part of the second heater or vice versa. However, it may be preferred that the first and second heaters are arranged so that they are interleaved or arranged side-by-side, that is so that they extend substantially in a common plane. In other words, the first and second heaters may have a complementary shape and may be arranged together to form the heater assembly without overlapping. The common plane is not necessarily flat, but may have any suitable shape. For example, if the first and second heaters are tubular or cylindrical, the first and second heaters may be interleaved so that they extend in a common plane that is substantially cylindrical. Interleaving the first and second heaters may provide a small and compact heater assembly that may be conveniently installed in a housing or main body of the aerosol generating device. A tubular or cylindrical heater may have any suitable crosssection, e.g., circular, elliptical or polygonal etc. The hottest and coldest regions of a heat distribution pattern associated with a tubular or cylindrical heater may be diametrically opposed.

[0023] The heater assembly may have an associated heat distribution pattern that has substantially no hotter or cooler regions (or where the difference between the temperature of the hotter and cooler regions and an average temperature is minimised) so that the heater assembly provides more even and consistent heating of the aerosol generating article. Put another way, the difference between the temperature of the hotter and cooler regions (or between the hottest and coolest regions) of the heater assembly may be less than the corresponding difference for the individual first and second heaters.

[0024] P51844WO-6722 The controller may be adapted to operate just one of the first and second heaters, i.e., so that the aerosol generating article is only heated by one of the first and second heaters. However, for the reasons explained above, it is preferred that the controller is adapted to operate the first and second heaters simultaneously, i.e., so that the aerosol generating article is heated by both of the first and second heaters at the same time, during at least one phase of a vaping session. It will be understood that such simultaneous operation does not necessarily mean that both of the first and second heaters will be turned on at the same time, because they are operated according to their respective duty cycles. In other words, when the first heater is being operated it will be repeatedly turned on and off according to the first duty cycle and when the second heater is being operated it will be repeatedly turned on and off according to the second duty cycle. Depending on the first and second duty cycles, this means that when both of the first and second heaters are being simultaneously operated by the controller, there may be times when the first and second heaters are both turned on, times when the first and second heaters are both turned off, times when the first heater is turned on and the second heater is turned off, and times when the first heater is turned off and the second heater is turned on. When operated by the controller, the first heater will heat the aerosol generating article according to the associated first heat distribution pattern. When operated by the controller, the second heater will heat the aerosol generating article according to the associated second heat distribution pattern. When both of the first and second heaters are being operated simultaneously, the aerosol generating article will be heated according to the combined first and second heat distribution patterns - i.e., the heat distribution pattern associated with the heater assembly as described in more detail below.

[0025] The first heater may be used as a main or primary heater to provide the main heating of the aerosol generating article, e.g., during pre-heating or for controlled heating for aerosol generation during a vaping session. The second heater may be used as a secondary heater to at least partially compensate for the reduced heating generated by the first heater at the cooler region(s) to provide more even or consistent heating of the aerosol generating article.

[0026] When the first heater is not operated by the controller, the first duty cycle is 0%.

[0027] When the second heater is not operated by the controller, the second duty cycle is 0%.

[0028] The first and second duty cycles may be complementary. More particularly, the first and second duty cycles may have the same cycle period and where, for each cycle period, one of the first and second heaters is initially turned on for the selected pulse width and then turned off for the remainder of the cycle period, and the other of the first and second heaters is initially turned off and is then turned on for the selected pulse width. For example, if both the first and second duty cycles are 90% and are complementary, with the same cycle period, the first heater may be turned on for the first 90% of each cycle period (e.g., for the first 90 ms if the cycle period is 100 ms) and then turned off for the remaining

[0029] P51844WO-6722 10% of each cycle period (e.g., for the remaining 10 ms of each cycle period). However, the second heater may be initially turned off for the first 10% of each cycle period (e.g., for the first 10 ms) and then turned on for the remaining 90% of each cycle period (e.g., for the remaining 90 ms of each cycle period). This means that the first and second heaters are only turned on at the same time for 70% (e.g., 70 ms) of each cycle. Using complementary first and second duty cycles therefore minimises the amount of time when both of the first and second heaters are turned on, thereby reducing the power demands on the energy storage device of the aerosol generating device.

[0030] The first and second duty cycles may be selected so that the first and second heaters are not both turned on at the same time even when they are both operated simultaneously by the controller and are both being used to heat the aerosol generating article. This may be done using complementary first and second duty cycles whose sum is less than 100%. For example, the first duty cycle may be 63% and the second duty cycle may be 27%, which would provide a total duty cycle of 90% for the heater assembly. For example, if the first and second duty cycles are complementary, with the same cycle period, the first heater may be turned on for the first 63% of each cycle period (e.g., for the first 63 ms if the cycle period is 100 ms) and then turned off for the remaining 37% of each cycle period (e.g., for the remaining 37 ms of each cycle period). However, the second heater may be initially turned off for the first 73% of each cycle period (e.g., for the first 73 ms) and then turned on for the remaining 27% of each cycle period (e.g., for the remaining 27 ms of each cycle period). The duty cycle of the heater assembly is therefore 90% and the first and second heaters are not turned on at the same time. In fact, for 10% (e.g., 10 ms) of each cycle, both of the first and second heaters are turned off.

[0031] The controller may be adapted to vary the first duty cycle and / or the second duty cycle over the course of a vaping session, e.g., for different phases such as pre-heating, controlled cool down, controlled heating etc. In certain phases, such as controlled cool down, the first duty cycle and / or the second duty cycle may be set to zero or the first heater and / or the second heater may not be operated by the controller. The duty cycle of the heater assembly may be varied by the controller and the first and second duty cycles for the first and second heaters may be adjusted according to a ratio based on the duty cycle for the heater assembly. For example, if the first and second heaters have a ratio for heating distribution of 70:30 that reflects the fact that they are to be used as primary and secondary heaters, respectively, and the duty cycle of the heater assembly is adjusted from 90% to 60%, the first duty cycle may be adjusted from 63% to 42% and the second duty cycle may be adjusted from 27% to 18%. If the duty cycle for the heater assembly is 30% the first duty cycle may be 21% and the second duty cycle may be 9%, for example. If the duty cycle for the heater assembly is 20%, the first duty cycle may be 14% and the second duty cycle may be 6%, for example.

[0032] The first duty cycle and / or the second duty cycle may also be adjusted by the controller based on a target temperature or a temperature profile. For example, using closed-loop control the first duty cycle and / or

[0033] P51844WO-6722 the second duty cycle may be adjusted based on the error between a measured temperature and a target temperature, or a temperature profile where the target temperature varies for the different phases of the vaping session. For example, if the measured temperature is below the target temperature or temperature profile, the pulse width of the first duty cycle and / or the second duty cycle may be increased to provide increased heating of the aerosol generating device or vice versa. The measured temperature may be a temperature of the aerosol generating device such as a temperature of the heating chamber, or a temperature of one or both of the first and second heaters. The measured temperature may also be a temperature of the aerosol generating article such as an external or surface temperature, or an internal temperature taken within the aerosol generating material, for example. The temperature may be measured by a suitable temperature sensor and the temperature measurements may be provided to the controller. Because the first heater is typically used as a main or primary heater, at least the first duty cycle will normally be adjusted based on closed-loop control for accurate and controllable heating of the aerosol generating article. The second duty cycle may also be adjusted to ensure that the even and consistent heating of the aerosol generating article is maintained, particularly during certain phases of the vaping session. It may also be important to adjust the second duty cycle during certain phases such as pre-heating where the second heater may also be used to rapidly raise the temperature of the aerosol generating article. In other phases, the second heater may be used mainly to heat the area of the aerosol generating article that is aligned with the cooler region(s) of the first heater and compensate for uneven heat distribution.

[0034] The aerosol generating device may comprise an energy storage device, e.g., a rechargeable battery such as a lithium-ion battery, a capacitor, or other suitable power source. In one arrangement, the energy storage device is a lithium-ion capacitor. The inherent characteristics of lithium-ion capacitors make them particularly suitable for use in aerosol generating devices. These inherent characteristics include:

[0035] - Low risk of thermal runaway - the chemical structure and energy storage mechanism of lithium- ion capacitors makes them less prone to thermal runaway, where the temperature increases rapidly and uncontrollably.

[0036] - Improved thermal stability - lithium-ion capacitors typically have good thermal stability and may operate safely over a wide range of temperatures without risk of overheating. This may be important in aerosol generating devices where the energy storage device may be subjected to heating.

[0037] - Lower energy density - lithium-ion capacitors may store less energy than some other known energy storage devices, but in the event of a failure this may significantly reduce the negative effects on the aerosol generating device.

[0038] - Enhanced safety features - lithium-ion capacitors may include additional safety features such as built-in overcharge protection, over-discharge protection and short-circuit protection, for example.

[0039] P51844WO-6722 - Extended cycle life - lithium-ion capacitors typically have an extended cycle life which means that they may be charged and discharged many times before they degrade significantly. This reduces the likelihood of failures over time.

[0040] - Rapid charge and discharge capabilities - lithium-ion capacitors may be charged and discharged rapidly without significant heat generation, which means that even with heavy use of an aerosol generating device (e.g., frequent vaping sessions) the energy storage device remains cool and stable.

[0041] The energy storage device may be electrically connected to the first heater by a first switching circuit and to the second heater by a second switching circuit. The first switching circuit may include at least one first semiconductor switch, for example, which may be turned on and off to control the supply of power from the energy storage device to the first heater. Similarly, the second switching circuit may include at least one second semiconductor switch, for example, which may be turned on and off to control the supply of power from the energy storage device to the second heater. The controller may be adapted to control the first switching circuit to supply power from the energy storage device to the first heater according to the first duty cycle (e.g., by repeatedly turning the at least one first semiconductor switch on and off) and to control the second switching circuit to supply power from the energy storage device to the second heater according to the second duty cycle (e.g., by repeatedly turning the at least one second semiconductor switch on and off). The controller may be a microcontroller unit (MCU) with control terminals that are electrically connected to the control terminals of the semiconductor switches (e.g., to the gate terminals). Each control terminal of the MCU is preferably independently connected to the control terminal of a respective semiconductor switch. The MCU may independently output control signals to the semiconductor switches to turn them on and off- e.g., where the control signal has a low- voltage level and a high-voltage level for controlling the switching. The first and second semiconductor switches may be of any suitable type.

[0042] According to a second aspect of the present disclosure, there is provided a method of heating an aerosol generating article comprising aerosol generating material, the method comprising: controlling a first heater using a first duty cycle to heat an area of the aerosol generating article according to an associated first heat distribution pattern with at least one region that is cooler than at least one other region; and controlling a second heater using a second duty cycle to heat at least part of the same area of the aerosol generating article according to an associated second heat distribution pattern with at least one region that is hotter that at least one other region; wherein the at least one hotter region of the second heat distribution pattern is substantially aligned with the at least one cooler region of the first heat distribution pattern so that the heat generated by the second heater at least partially compensates for reduced heating generated by the first heater at

[0043] P51844WO-6722 the cooler region(s) of the first heat distribution pattern to provide more even heating of the aerosol generating article.

[0044] The first and second duty cycles may be complementary as described in more detail above.

[0045] The method may be implemented using a controller of an aerosol generating device as described in more detail above.

[0046] According to a third aspect of the present disclosure, there is provided a method of heating an aerosol generating article comprising aerosol generating material using a heater assembly comprising a first heater and a second heater that are arranged (e.g., interleaved) such that the first and second heaters extend substantially in a common plane, the method comprising: using the first heater to heat an area of the aerosol generating article according to an associated first heat distribution pattern with at least one region that is cooler than at least one other region; and using the second heater to heat at least part of the same area of the aerosol generating article according to an associated second heat distribution pattern with at least one region that is hotter that at least one other region; wherein the at least one hotter region of the second heat distribution pattern is substantially aligned with the at least one cooler region of the first heat distribution pattern so that the heat generated by the second heater at least partially compensates for reduced heating generated by the first heater at the cooler region(s) of the first heat distribution pattern to provide more even heating of the aerosol generating article.

[0047] The first heater may be controlled using a first duty cycle.

[0048] The second heater may be controlled using a second duty cycle.

[0049] The first and second duty cycles may be complementary.

[0050] The method may be implemented using a controller of the aerosol generating device as described in more detail above.

[0051] According to a fourth aspect of the present disclosure, there is provided a method of heating an aerosol generating article comprising: using a first heater to heat an area of the aerosol generating article using a first duty cycle; and using a second heater to heat at least part of the same area of the aerosol generating article using a second duty cycle; wherein the first and second duty cycles are complementary.

[0052] P51844WO-6722 The first heater and the second heater may be interleaved or arranged side-by-side as described in more detail above such that the first and second heaters extend substantially in a common plane.

[0053] The first heater may heat the area of the aerosol generating article according to an associated first heat distribution pattern with at least one region that is cooler than at least one other region. The second heater may heat the at least part of the same area of the aerosol generating article according to an associated second heat distribution pattern with at least one region that is hotter than at least one other region. As described in more detail above, the at least one hotter region of the second heat distribution pattern may be substantially aligned with the at least one cooler region of the first heat distribution pattern so that the heat generated by the second heater at least partially compensates for reduced heating generated by the first heater at the cooler region(s) of the first heat distribution pattern to provide more even heating of the aerosol generating article.

[0054] The method may be implemented using a controller of the aerosol generating device as described in more detail above.

[0055] The aerosol generating article may comprise aerosol generating material.

[0056] The aerosol generating material may comprise any type of solid or semi-solid material. Example types of aerosol generating solids include powder, granules, pellets, shreds, strands, particles, gel, strips, loose leaves, cut filler, porous material, foam material or sheets. The aerosol generating material may comprise plant derived material and in particular, may comprise tobacco. It may advantageously comprise reconstituted tobacco, for example including tobacco and any one or more of cellulose fibres, tobacco stalk fibres and inorganic fillers. The solid or semi-solid aerosol generating material may be heated by the heater of the aerosol generating aerosol generating device - e.g., when arranged in the heating chamber.

[0057] The aerosol generating material may comprise an aerosol-former. Examples of aerosol-formers include polyhydric alcohols and mixtures thereof such as glycerine or propylene glycol. Typically, the aerosol generating material may comprise an aerosol-former content of between approximately 5% and approximately 50% on a dry weight basis. In some embodiments, the aerosol generating material may comprise an aerosol-former content of between approximately 10% and approximately 22% on a dry weight basis, and possibly approximately 15% on a dry weight basis.

[0058] The aerosol generating device may be adapted to heat the aerosol generating material or substrate, without burning the aerosol generating material, to volatise at least one component of the aerosol generating material and thereby generate a heated vapour which cools and condenses to form an aerosol

[0059] P51844WO-6722 for inhalation by a user of the aerosol generating device. The volatile compounds released from the aerosol generating material may include nicotine or flavour compounds such as tobacco flavouring.

[0060] In general terms, a vapour is a substance in the gas phase at a temperature lower than its critical temperature, which means that the vapour may be condensed to a liquid by increasing its pressure without reducing the temperature, whereas an aerosol is a suspension of fine solid particles or liquid droplets, in air or another gas. It should, however, be noted that the terms ‘aerosol’ and ‘vapour’ may be used interchangeably in this specification, particularly with regard to the form of the inhalable medium that is generated for inhalation by a user.

[0061] When the aerosol generating material is depleted, the aerosol generating article may be removed from the aerosol generating device and a new article may be inserted.

[0062] The aerosol generating article may comprise a mouthpiece through which the generated aerosol may be inhaled.

[0063] According to a fifth aspect of the present disclosure, there is provided an aerosol generating system comprising: an aerosol generating device as described above, and an aerosol generating article as described above, received in the heating chamber of the aerosol generating device in use.

[0064] Brief Description of the Drawings

[0065] Figure 1 is a diagrammatic view of a flat heater;

[0066] Figure 2 is a diagrammatic view of a heat distribution pattern of the flat heater of Figure 1 ;

[0067] Figure 3 is a diagrammatic view of a cylindrical heater;

[0068] Figure 4 is a diagrammatic view of a heat distribution pattern of the cylindrical heater of Figure 3;

[0069] Figure 5 is a diagrammatic view of an aerosol generating system comprising an aerosol generating device and an aerosol generating article;

[0070] Figure 6 is a diagrammatic view of a first heater of a first heater assembly of the aerosol generating device of Figure 5;

[0071] Figure 7 is a diagrammatic view of a second heater of the first heater assembly of the aerosol generating device of Figure 5;

[0072] Figure 8 is a diagrammatic view of the first heater assembly of the aerosol generating device of Figure 5;

[0073] Figure 9 is a diagrammatic view of a heat distribution pattern of the first heater of Figure 6;

[0074] Figure 10 is a diagrammatic view of a heat distribution pattern of the second heater of Figure 7;

[0075] Figure 11 is a diagrammatic view of a heat distribution pattern of the first heater assembly of Figure 8;

[0076] P51844WO-6722 Figure 12 is a diagrammatic view of a first heater of a second heater assembly of the aerosol generating device of Figure 5;

[0077] Figure 13 is a diagrammatic view of a second heater of the second heater assembly of the aerosol generating device of Figure 5;

[0078] Figure 14 is a diagrammatic view of the second heater assembly of the aerosol generating device of Figure 5;

[0079] Figure 15 is a diagrammatic view of a heat distribution pattern of the first heater of Figure 12;

[0080] Figure 16 is a diagrammatic view of a heat distribution pattern of the second heater of Figure 13;

[0081] Figure 17 is a diagrammatic view of a heat distribution pattern of the second heater assembly of Figure 14;

[0082] Figure 18 is a diagrammatic view of a first heater of a third heater assembly of the aerosol generating device of Figure 5;

[0083] Figure 19 is a diagrammatic view of a second heater of the third heater assembly of the aerosol generating device of Figure 5;

[0084] Figure 20 is a diagrammatic view of the third heater assembly of the aerosol generating device of Figure 5;

[0085] Figure 21 is a diagrammatic view of a heat distribution pattern of the first heater of Figure 18;

[0086] Figure 22 is a diagrammatic view of a heat distribution pattern of the second heater of Figure 19;

[0087] Figure 23 is a diagrammatic view of a heat distribution pattern of the third heater assembly of Figure 20; Figure 24 is a circuit diagram of a control circuit of the aerosol generating device of Figure 5;

[0088] Figure 25 is an example of a heating profile for a vaping session;

[0089] Figure 26 is a first example of complementary duty cycles for the first and second heaters of a heater assembly; and

[0090] Figure 27 is a second example of complementary duty cycles for the first and second heaters of a heater assembly.

[0091] Detailed Description of Embodiments

[0092] Embodiments of the present disclosure will now be described by way of example only and with reference to the accompanying drawings.

[0093] Referring initially to Figure 5, there is shown diagrammatically an example of an aerosol generating system 1. The aerosol generating system 1 comprises an aerosol generating device 10 and an aerosol generating article 100 for use with the device 10. The aerosol generating device 10 comprises a main body 12 housing various components of the aerosol generating device 10. The main body 12 may have any shape that is sized to fit the components described in the various embodiments set out herein and to be comfortably held by a user unaided, in a single hand.

[0094] P51844WO-6722 A first end 14 of the aerosol generating device 10, shown towards the bottom of Figure 5, is described for convenience as a distal, bottom, base or lower end of the aerosol generating device 10. A second end 16 of the aerosol generating device 10, shown towards the top of Figure 5, is described as a proximal, top or upper end of the aerosol generating device 10. During use, the user typically orients the aerosol generating device 10 with the first end 14 downward and / or in a distal position with respect to the user’s mouth and the second end 16 upward and / or in a proximate position with respect to the user’s mouth.

[0095] The aerosol generating device 10 comprises a heating chamber 18 positioned in the main body 12. The heating chamber 18 defines an interior volume in the form of a cavity 20 having a substantially cylindrical cross-section for receiving an aerosol generating article 100. The cavity may have any other suitable cross-section that is sized and shaped to receive the aerosol generating article 100. The heating chamber 18 has a longitudinal axis defining a longitudinal direction and is formed of a heat-resistant plastics material, such as poly ether ether ketone (PEEK). The aerosol generating device 10 further comprises an energy storage device 22, for example a lithium-ion capacitor or one or more batteries which are rechargeable, for example, and a control circuit 24. The control circuit 24 may comprise one or more integrated circuits (ICs) and other electronic components. For example, the control circuit 24 may comprise at least a microcontroller unit (MCU) 58. The control circuit 24 may comprise a printed circuit board assembly (PCBA) with a rigid printed circuit board (PCB) on which the one or more electronic components or ICs are mounted. A flexible PCB may also be used.

[0096] The heating chamber 18 is open towards the second end 16 of the aerosol generating device 10. In other words, the heating chamber 18 has an open first end 26 towards the second end 16 of the aerosol generating device 10. The heating chamber 18 is typically held spaced apart from the inner surface of the main body 12 to minimise heat transfer to the main body 12.

[0097] The aerosol generating device 10 may optionally include a sliding cover 28 movable transversely between a closed position (shown in Figure 5) in which it covers the open first end 26 of the heating chamber 18 to prevent access to the heating chamber 18 and an open position (not shown) in which it exposes the open first end 26 of the heating chamber 18 to provide access to the heating chamber 18. The sliding cover 28 may be biased to the closed position in some embodiments.

[0098] The heating chamber 18, and specifically the cavity 20, is arranged to receive a correspondingly shaped generally cylindrical or rod-shaped aerosol generating article 100. Typically, the aerosol generating article 100 comprises a pre-packaged aerosol generating material or substrate 102. The aerosol generating article 100 is a disposable and replaceable article (also known as a “consumable”) which may, for example, contain tobacco as the aerosol generating material 102. The aerosol generating article 100 has a proximal end 104 (or mouth end) and a distal end 106. The aerosol generating article 100 further comprises a mouthpiece segment 108 positioned downstream of the aerosol generating material 102. The

[0099] P51844WO-6722 aerosol generating material 102 and the mouthpiece segment 108 are arranged in coaxial alignment inside a wrapper 110 (e.g., a paper wrapper) to hold the components in position to form the rod-shaped aerosol generating article 100.

[0100] The mouthpiece segment 108 may comprise one or more of the following components (not shown in detail) arranged sequentially and in co-axial alignment in a downstream direction, in other words from the distal end 106 towards the proximal (mouth) end 104 of the aerosol generating article 100: a cooling segment, a centre hole segment and a filter segment. The cooling segment typically comprises a hollow paper tube having a thickness which is greater than the thickness of the wrapper 110. The centre hole segment may comprise a cured mixture containing cellulose acetate fibres and a plasticizer, and functions to increase the strength of the mouthpiece segment 108. The filter segment typically comprises cellulose acetate fibres and acts as a mouthpiece filter. As heated vapour flows from the aerosol generating material 102 towards the proximal (mouth) end 104 of the aerosol generating article 100, the vapour cools and condenses as it passes through the cooling segment and the centre hole segment to form an aerosol with suitable characteristics for inhalation by a user through the filter segment.

[0101] The heating chamber 18 has a side wall (or chamber wall) 30 extending between a base 32, located at a second end 34 of the heating chamber 18, and the open first end 26. The side wall 30 and the base 32 are connected to each other and may be integrally formed as a single piece. In the illustrated embodiment, the side wall 30 is tubular and, more specifically, cylindrical. The side wall 30 may be formed so that the cross-section of the heating chamber 18 is a perfect circle or an ellipse. In other embodiments, the side wall 30 may have other suitable shapes, such as a tube with an elliptical or polygonal cross-section. In yet further embodiments, the side wall 30 may be tapered.

[0102] In the illustrated embodiment, the base 32 of the heating chamber 18 is closed, e.g., sealed or air-tight. That is, the heating chamber 18 is cup-shaped. This may ensure that air drawn from the open first end 26 is prevented by the base 32 from flowing out of the second end 34 and is instead guided through the aerosol generating material 102. It may also ensure that a user inserts the aerosol generating article 100 into the heating chamber 18 an intended distance and no further.

[0103] The device 10 includes a heater assembly 36, which is configured to heat the aerosol generating material 102 when the aerosol generating article 100 is received in the heating chamber 18.

[0104] The heater assembly 36 shown in Figure 5 may comprise a pair of flat heater assemblies that are arranged adjacent the heating chamber 18, or a cylindrical heater assembly that extends around the heating chamber 18, for example.

[0105] P51844WO-6722 An example of a first heater assembly 36A for the aerosol generating device 10 is shown in Figures 6 to 8. The first heater assembly 36A is a cylindrical (or tubular) heater having a serpentine construction. The first heater assembly 36A includes a first heater 38 that is formed as an electrically conductive heating element with a first end part 40, a second end part 42, and an intermediate part 44 that extends between the first and second end parts 40, 42. The first heater assembly 36A also includes a second heater 46 that is formed as an electrically conductive heating element with a first end part 48, a second end part 50, and an intermediate part 52 that extends between the first and second end parts 48, 50. The first and second end parts 40, 42 of the first heater 38 may provide a way of electrically connecting the first heater 38 to a first switching circuit 60 described in more detail below. Similarly, the first and second end parts 48, 50 of the second heater 46 may provide a way of electrically connecting the second heater 46 to a second switching circuit 62 described in more detail below. Both heating elements have a plurality of turns. Although the first heater assembly 36A, and the first and second heaters 38, 46, are cylindrical, it will be understood that the present disclosure is not limited to cylindrical heaters and that in practice the heaters may have any suitable shape, e.g., they may also be flat heaters that are shaped so that when interleaved or arranged side-by-side in a common plane the heater assembly provides more even and consistent heating because the heat generated by the second heater compensates for reduced heating generated by the first heater at its cooler region(s). In some arrangements, two or more second heaters may be provided, where each second heater is positioned to compensate for reduced heating at a respective cooler region of the first heater.

[0106] The first heater 38 has a pair of gaps 54a, 54b. Each gap 54a, 54b is defined by a wider turn - i.e., a turn where the gap in the circumferential direction between the axially extending parts of the serpentine heater element is wider than the other turns. The second heater 46 has a pair of turns 56a, 56b. It may therefore be seen that the first and second heaters 38, 46 have a complementary shape so that they may be arranged together to form the first heater assembly 36A without overlapping. In particular, the first and second heaters 38, 46 are interleaved as shown in Figure 8 so that they extend in a common cylindrical plane with the turns 56a, 56b of the second heater 46 positioned in the gaps 54a, 54b of the first heater 38. The part of the intermediate part 44 of the first heater 38 that is diametrically opposite the first and second end parts 40, 42 is substantially aligned with the first and second end parts 48, 50 of the second heater 46, and the part of the intermediate part 52 of the second heater 46 that is diametrically opposite the first and second end parts 48, 50 is substantially aligned with the first and second parts 40, 42 of the first heater 38. Interleaving the first and second heaters 38, 46 provides a small and compact first heater assembly 36A that may be conveniently installed in the main body 12 of the aerosol generating device 10. The same area of the aerosol generating article 100 is heated by both the first and second heaters 38, 46 during a vaping session, i.e., when the aerosol generating device 10 is used to heat the aerosol generating article 100 that is received in the heating chamber 18 to generate an aerosol that is inhaled by the user.

[0107] P51844WO-6722 The first and second heat distribution patterns associated with the first and second heaters 38, 46 are shown in Figures 9 and 10. The heat distribution pattern of the first heater assembly 36A is shown in Figure 11. In each case, the coldest region is shown with the lowest density of shading and the hottest region is shown with the highest density of shading. It may be seen that the coldest region of the first heat distribution pattern is where the first and second ends 40, 42 meet, and the hottest region is at the part of the intermediate part 44 that is diametrically opposite. It may also be seen that the coldest region of the second heat distribution pattern is where the first and second ends 48, 50 meet, and the hottest region is at the part of the intermediate part 52 that is diametrically opposite. The hottest and coldest regions of the first and second heat distribution patterns are therefore diametrically opposed.

[0108] The hottest region of the second heat distribution pattern associated with the second heater 46 is substantially aligned with the coldest region of the first heat distribution pattern associated with the first heater 38. In other words, the heat generated by the second heater 46 at least partially compensates for reduced heating generated by the first heater 38 at the coldest region to provide more even or consistent heating of the area of the aerosol generating article 100 when the first and second heaters 38, 46 are operated at the same time. The coldest region of the second heat distribution pattern associated with the second heater 46 is substantially aligned with the hottest region of the first heat distribution pattern associated with the first heater 38. The first heater assembly 36A provides a more even heat distribution than using a single heater - see the heat distribution pattern shown in Figure 11, for example.

[0109] An example of a second heater assembly 36B for the aerosol generating device 10 is shown in Figures 12 to 14. The second heater assembly 36B is a cylindrical (or tubular) heater having a serpentine construction. The second heater assembly 36B includes a first heater 38 that is formed as an electrically conductive heating element with a first end part 40, a second end part 42, and an intermediate part 44 that extends between the first and second end parts 40, 42. The second heater assembly 36B also includes a second heater 46 that is formed as an electrically conductive heating element with a first end part 48, a second end part 50, and an intermediate part 52 that extends between the first and second end parts 48, 50. The first and second end parts 40, 42 of the first heater 38 may provide a way of electrically connecting the first heater 38 to a first switching circuit 60 described in more detail below. Similarly, the first and second end parts 48, 50 of the second heater 46 may provide a way of electrically connecting the second heater 46 to a second switching circuit 62 described in more detail below. Both heating elements have a plurality of turns.

[0110] The turns at one axial end of the first heater 38 are wider than the turns at the opposite axial end of the first heater 38 to define a series of wider gaps 54. The second heater 46 has a complementary shape where the turns 56 at one axial end of the second heater 46 are narrower than the turns at the opposite axial end of the second heater 46. It may therefore be seen that the first and second heaters 38, 46 have a complementary shape so that they may be arranged together to form the second heater assembly 36B

[0111] P51844WO-6722 without overlapping. In particular, the first and second heaters 38, 46 are interleaved as shown in Figure 14 so that they extend in a common cylindrical plane with the narrower turns 56 of the second heater 46 positioned in the wider gaps 54 of the first heater 38. The narrower turns of the first heater 38 at the opposite axial end of the first heater 38 are also positioned in the wider gaps of the second heater 46 as shown in Figure 14. The part of the intermediate part 44 of the first heater 38 that is diametrically opposite the first and second end parts 40, 42 is substantially aligned with the first and second end parts 48, 50 of the second heater 46, and the part of the intermediate part 52 of the second heater 46 that is diametrically opposite the first and second end parts 48, 50 is substantially aligned with the first and second parts 40, 42 of the first heater 38. Interleaving the first and second heaters 38, 46 provides a small and compact second heater assembly 36B that may be conveniently installed in the main body 12 of the aerosol generating device 10. The same area of the aerosol generating article 100 is heated by both the first and second heaters 38, 46 during a vaping session, i.e., when the aerosol generating device 10 is used to heat the aerosol generating article 100 that is received in the heating chamber 18 to generate an aerosol that is inhaled by the user.

[0112] The first and second heat distribution patterns associated with the first and second heaters 38, 46 are shown in Figures 15 and 16. The heat distribution pattern of the second heater assembly 36B is shown in Figure 17. In each case, the coldest region is shown with the lowest density of shading and the hottest region is shown with the highest density of shading. It may be seen that the coldest region of the first heat distribution pattern is where the first and second ends 40, 42 meet, and the hottest region is at the part of the intermediate part 44 diametrically opposite. It may also be seen that the coldest region of the second heat distribution pattern is where the first and second ends 48, 50 meet, and the hottest region is at the part of the intermediate part 52 diametrically opposite. The hottest and coldest regions of the first and second heat distribution patterns are therefore diametrically opposed.

[0113] The hottest region of the second heat distribution pattern associated with the second heater 46 is substantially aligned with the coldest region of the first heat distribution pattern associated with the first heater 38. In other words, the heat generated by the second heater 46 at least partially compensates for reduced heating generated by the first heater 38 at the coldest region to provide more even or consistent heating of the area of the aerosol generating article 100 when the first and second heaters 38, 46 are operated at the same time. The coldest region of the second heat distribution pattern associated with the second heater 46 is substantially aligned with the hottest region of the first heat distribution pattern associated with the first heater 38. The second heater assembly 36B provides a more even heat distribution than using a single heater - see the heat distribution pattern shown in Figure 17, for example.

[0114] An example of a third heater assembly 36C for the aerosol generating device 10 is shown in Figures 18 to 20. The third heater assembly 36C is a cylindrical (or tubular) heater having a serpentine construction. The third heater assembly 36C includes a first heater 38 that is formed as an electrically conductive

[0115] P51844WO-6722 heating element with a first end part 40, a second end part 42, and an intermediate part 44 that extends between the first and second end parts 40, 42. The third heater assembly 36C also includes a second heater 46 that is formed as an electrically conductive heating element with a first end part 48, a second end part 50, and an intermediate part 52 that extends between the first and second end parts 48, 50. The first and second end parts 40, 42 of the first heater 38 may provide a way of electrically connecting the first heater 38 to a first switching circuit 60 described in more detail below. Similarly, the first and second end parts 48, 50 of the second heater 46 may provide a way of electrically connecting the second heater 46 to a second switching circuit 62 described in more detail below. Both heating elements have a plurality of turns.

[0116] The length of the axially extending parts of the tuns of the first and second heaters 38, 46 varies along the circumferential direction. In particular, turn length in the axial direction is smallest at the first and second end parts 40, 42 of the first heater 38 and increases gradually along the circumferential direction with the turn length in the axial direction being the largest at the part of the intermediate part 44 that is diametrically opposite the first and second end parts 40, 42 as shown in Figure 18. Turn length in the axial direction is smallest at the first and second end parts 48, 50 of the second heater 46 and increases gradually along the circumferential direction with the turn length in the axial direction being the largest at the part of the intermediate part 52 that is diametrically opposite the first and second end parts 48, 50 as shown in Figure 19. It may therefore be seen that the first and second heaters 38, 46 have a complementary shape so that they may be arranged together side-by-side to form the third heater assembly 36C without overlapping. In particular, the first and second heaters 38, 46 are arranged as shown in Figure 20 so that they extend in a common cylindrical plane where the part of the intermediate part 44 of the first heater 38 that is diametrically opposite the first and second end parts 40, 42 is substantially aligned with the first and second end parts 48, 50 of the second heater 46, and the part of the intermediate part 52 of the second heater 46 that is diametrically opposite the first and second end parts 48, 50 is substantially aligned with the first and second parts 40, 42 of the first heater 38. Arranging the first and second heaters 38, 46 side-by-side in a common plane provides a small and compact third heater assembly 36C that may be conveniently installed in the main body 12 of the aerosol generating device 10. The same area of the aerosol generating article 100 is heated by both the first and second heaters 38, 46 during a vaping session, i.e., when the aerosol generating device 10 is used to heat the aerosol generating article 100 that is received in the heating chamber 18 to generate an aerosol that is inhaled by the user.

[0117] The first and second heat distribution patterns associated with the first and second heaters 38, 46 are shown in Figures 21 and 22. The heat distribution pattern of the third heater assembly 36C is shown in Figure 23. In each case, the coldest region is shown with the lowest density of shading and the hottest region is shown with the highest density of shading. It may be seen that the coldest region of the first heat distribution pattern is where the first and second ends 40, 42 meet, and the hottest region is at the

[0118] P51844WO-6722 part of the intermediate part 44 diametrically opposite. It may also be seen that the coldest region of the second heat distribution pattern is where the first and second ends 48, 50 meet, and the hottest region is at the part of the intermediate part 52 diametrically opposite. The hottest and coldest regions of the first and second heat distribution patterns are therefore diametrically opposed.

[0119] The hottest region of the second heat distribution pattern associated with the second heater 46 is substantially aligned with the coldest region of the first heat distribution pattern associated with the first heater 38. In other words, the heat generated by the second heater 46 at least partially compensates for reduced heating generated by the first heater 38 at the coldest region to provide more even or consistent heating of the area of the aerosol generating article 100 when the first and second heaters 38, 46 are operated at the same time. The coldest region of the second heat distribution pattern associated with the second heater 46 is substantially aligned with the hottest region of the first heat distribution pattern associated with the first heater 38. The third heater assembly 36C provides a more even heat distribution than using a single heater - see the heat distribution pattern shown in Figure 23, for example.

[0120] Referring to Figure 24, the control circuit 24 of the aerosol generating device 10 includes a MCU 58. The energy storage device 22 is electrically connected to the first heater 38 by a first switching circuit 60 that includes a first semiconductor switch QI . The energy storage device 22 is electrically connected to the second heater 46 by a second switching circuit 62 that includes a second semiconductor switch Q2. The first and second switches QI, Q2 are turned on and off by the MCU 58 to control the supply of power from the energy storage device 22 to the first and second heaters 38, 46. In particular, the MCU 58 includes a first control terminal that outputs a first control signal to the control terminal of the first semiconductor switch QI to repeatedly turn it on and off according to a first duty cycle, and a second control terminal that outputs a second control signal to the control terminal of the second semiconductor switch Q2 to repeatedly turn it on and off according to a second duty cycle. The MCU 58 may control the first and second semiconductor switches QI , Q2 independently. When the first semiconductor switch QI is turned on, power is supplied from the energy storage device 22 to the first heater 38. When the second semiconductor switch Q2 is turned on, power is supplied from the energy storage device 22 to the second heater 46.

[0121] The first and second duty cycles are adjusted independently by the MCU 58 to independently control the temperature and the heat generated by the first and second heaters 38, 46.

[0122] Figure 25 shows an example of a heating profile for a vaping session. The vaping session includes the following phases: fast pre-heating (Pl), controlled pre-heating (P2), controlled cool down (P3),

[0123] P51844WO-6722 - controlled heating (P4),

[0124] - maintaining heating (P5), and

[0125] - final cool down (P6).

[0126] Simply as an example, the fast pre-heating (Pl) is shown for time 0-6 seconds, controlled pre-heating (P2) is shown for time 6-25 seconds, controlled cool down (P3) is shown for time 25-50 seconds, controlled heating (P4) is shown for time 50-215 seconds, maintaining heating (P5) is shown for 215- 315 seconds, and final cool down (P6) is shown for 315 to 325 seconds. The whole vaping session, including the pre-heating, lasts for about 325 seconds. During the controlled heating and maintaining heating phases (P4, P5) the user may take several puffs to inhale the aerosol that is generated by heating the aerosol generating article 100.

[0127] The MCU 58 operates the first and second heaters 38, 46 simultaneously, i.e., so that the aerosol generating article 100 is heated by both of the first and second heaters 38, 46 at the same time, during at least one phase of a vaping session.

[0128] One example of how the first and second heaters 38, 46 may be controlled is set out in Table 1 below.

[0129] Table 1

[0130] Figure 26 shows the first and second duty cycles during the pre-heating phases (Pl, P2) where the duty cycle of the heater assembly 36 is 90%. (The heater assembly may be one of the first, second or third heater assemblies 36A, 36B, 36C described above.) It may be seen that the first and second duty cycles have the same cycle period (i.e., 100 ms) and are complementary as described above. In particular, the first heater 38 is turned on for the first 63% of each cycle period (e.g., for the first 63 ms if the cycle period is 100 ms) and then turned off for the remaining 37% of each cycle period (e.g., for the remaining 37 ms of each cycle period). The second heater 46 is initially turned off for the first 73% of each cycle period (e.g., for the first 73 ms) and then turned on for the remaining 27% of each cycle period (e.g., for the remaining 27 ms of each cycle period). This means that the first and second heaters 38, 46 are not

[0131] P51844WO-6722 turned on at the same time. Although the first and second duty cycles for the remaining phases are not shown, it will be understood that they will be similar to what is shown in Figure 14, but where the first heater 38 is turned on for the first 21% or 14% of each cycle period (e.g., for the first 21 ms or 14 ms) and then turned off for the remainder of each cycle period, and where the second heater 46 is initially turned off and is then turned on for the last 9% or 6% of each cycle period (e.g., for the last 9 or 6 ms). During the controlled cool down and final cool down (P3 and P6), the first and second heaters 38, 46 are not operated - the first and second duty cycles are 0%.

[0132] Another example of how the first and second heaters 38, 46 may be controlled is set out in Table 2 below.

[0133] Table 2

[0134] Figure 27 shows the first and second duty cycles during the fast pre-heating phase (Pl). It may be seen that the first and second duty cycles have the same cycle period (i.e., 100 ms) and are complementary as described above. In particular, the first heater 38 is turned on for the first 72% of each cycle period (e.g., for the first 72 ms if the cycle period is 100 ms) and then turned off for the remaining 28% of each cycle period (e.g., for the remaining 28 ms of each cycle period). The second heater 46 is initially turned off for the first 52% of each cycle period (e.g., for the first 52 ms) and then turned on for the remaining 48% of each cycle period (e.g., for the remaining 48 ms of each cycle period). This means that the first and second heaters 38, 46 are turned on at the same time for 20% of each cycle period (e.g., for 20 ms), thereby reducing the power demands on the energy storage device 22 as compared with using non- complementary duty cycles. Although the first and second duty cycles for the remaining phases are not shown, it will be understood that they will be similar to what is shown in Figure 15, but where the first heater 38 is turned on for the first 64-48%, 21% or 14% of each cycle period (e.g., for the first 64-48 ms, 21 ms or 14 ms) and then turned off for the remainder of each cycle period, and where the second heater 46 is initially turned off and is then turned on for the last 40-30%, 9% or 6% of each cycle period (e.g. for the last 40-30 ms, 9 ms or 5 ms). During the controlled cool down and final cool down (P3 and P6), the first and second heaters 38, 46 are not operated - the first and second duty cycles are 0%.

[0135] P51844WO-6722 Although the first and second duty cycles shown in Figures 14 and 15 have a cycle period of 100 ms, it will be understood that any suitable cycle period may be used.

[0136] The first duty cycle and / or the second duty cycle may also be adjusted by the MCU 58 based on a target temperature or a temperature profile. For example, using closed-loop control the first duty cycle and / or the second duty cycle may be adjusted based on the error between a measured temperature and a target temperature or temperature profile where the target temperature varies for the different phases of the vaping session. For example, if the measured temperature is below the target temperature or temperature profile, the pulse width of the first duty cycle and / or the second duty cycle may be increased to provide increased heating of the aerosol generating device 100 or vice versa. The measured temperature may be a temperature of the aerosol generating device 10 such as a temperature of the heating chamber 18, or of one or both of the first and second heaters 38, 46. The measured temperature may also be a temperature of the aerosol generating article 100 such as an external or surface temperature, or an internal temperature taken within the aerosol generating material 102, for example. The temperature may be measured by a suitable temperature sensor and the temperature measurements may be provided to the MCU 58. Because the first heater 38 is typically used as a main or primary heater, at least the first duty cycle will normally be adjusted based on closed-loop control for accurate and controllable heating of the aerosol generating article 100. The second duty cycle may also be adjusted to ensure that the even and consistent heating of the aerosol generating article 100 is maintained, particularly during certain phases of the vaping session. It may also be important to adjust the second duty cycle during certain phases such as pre-heating where the second heater 46 may also be used to rapidly raise the temperature of the aerosol generating article 100. In other phases, the second heater 46 may be used mainly to heat the area of the aerosol generating article 100 that is aligned with the cooler region of the first heater 38 and compensate for uneven heat distribution.

[0137] Although exemplary embodiments have been described in the preceding paragraphs, it should be understood that various modifications may be made to those embodiments without departing from the scope of the appended claims. Thus, the breadth and scope of the claims should not be limited to the above-described exemplary embodiments.

[0138] Any combination of the above-described features in all possible variations thereof is encompassed by the present disclosure unless otherwise indicated herein or otherwise clearly contradicted by context.

[0139] Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise”, “comprising”, and the like, are to be construed in an inclusive as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to”.

[0140] P51844WO-6722

Claims

- 23 -Claims1. An aerosol generating device (10) comprising: a heating chamber (18) adapted to receive an aerosol generating article (100) in use; a heater assembly (36; 36A; 36B; 36C) comprising: a first heater (38) adapted to heat an area of the aerosol generating article (100) when the aerosol generating article (100) is received in the heating chamber (18), and a second heater (46) adapted to heat at least part of the same area of the aerosol generating article (100) when the aerosol generating article (100) is received in the heating chamber (18); and a controller (58) adapted to control operation of the first heater (38) according to a first duty cycle and to control operation of the second heater (46) according to a second duty cycle; wherein the first heater (38) has an associated first heat distribution pattern with at least one region that is cooler than at least one other region; and wherein the second heater (46) has an associated second heat distribution pattern with at least one region that is hotter than at least one other region, and wherein the at least one hotter region of the second heat distribution pattern is substantially aligned with the at least one cooler region of the first heat distribution pattern.

2. An aerosol generating device (10) according to claim 1, wherein the at least one cooler region is the coldest region of the first heat distribution pattern, and the at least one hotter region is the hottest region of the second heat distribution pattern.

3. An aerosol generating device (10) according to claim 1 or claim 2, wherein the first and second heaters (38, 46) are resistive heaters.

4. An aerosol generating device (10) according to any preceding claim, wherein the first and second heaters (38, 46) are flat or tubular heaters arranged adjacent or around the heating chamber (18).

5. An aerosol generating device (10) according to any preceding claim, wherein the first and second heaters (38, 46) extend substantially in a common plane.

6. An aerosol generating device (10) according to any preceding claim, wherein the controller (58) is adapted to operate just one of the first and second heaters (38, 46).

7. An aerosol generating device (10) according to any of claims 1 to 5, wherein the controller (58) is adapted to operate the first and second heaters (38, 46) simultaneously.P51844WO-67228. An aerosol generating device (10) according to any preceding claim, wherein the first and second duty cycles are complementary.

9. An aerosol generating device (10) according to any preceding claim, wherein the controller (58) is adapted to vary the first duty cycle and / or the second duty cycle over the course of a vaping session.

10. An aerosol generating device (10) according to any preceding claim, further comprising an energy storage device (22).

11. An aerosol generating device (10) according to claim 10, wherein the energy storage device (22) is a lithium-ion capacitor.

12. An aerosol generating device (10) according to claim lO orclaim 11 , wherein the energy storage device (22) is electrically connected to the first heater (38) by a first switching circuit (60) and to the second heater (46) by a second switching circuit (62).

13. An aerosol generating device (10) according to claim 12, wherein the controller (58) is adapted to control the first switching circuit (60) to supply power from the energy storage device (22) to the first heater (38) according to the first duty cycle and to control the second switching circuit (62) to supply power from the energy storage device (22) to the second heater (46) according to the second duty cycle.

14. A method of heating an aerosol generating article (100) comprising aerosol generating material (102), the method comprising: controlling a first heater (38) using a first duty cycle to heat an area of the aerosol generating article (100) according to an associated first heat distribution pattern with at least one region that is cooler than at least one other region; and controlling a second heater (46) using a second duty cycle to heat at least part of the same area of the aerosol generating article (100) according to an associated second heat distribution pattern with at least one region that is hotter that at least one other region; wherein the at least one hotter region of the second heat distribution pattern is substantially aligned with the at least one cooler region of the first heat distribution pattern so that the heat generated by the second heater (46) at least partially compensates for reduced heating generated by the first heater (38) at the cooler region(s) of the first heat distribution pattern to provide more even heating of the aerosol generating article (100).

15. A method according to claim 14, wherein the first and second duty cycles are complementary.P51844WO-6722

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