Aerosol generating device

Abstract

The generating device (10) comprises: a heating chamber (18) configured to receive a consumable (100) comprising an aerosol-generating substrate (102); a heating assembly operable to supply heat to the aerosol-generating substrate during a use session; and a controller (24). The controller is operable to monitor a considerable measure indicative of a moisture content of the aerosol-generating substrate during the use session; and progressively providing to a user an indication of the moisture content of the aerosol-generating substrate during the use session. The observable measurement may be a delay associated with an RC monitoring circuit having a predetermined time constant. A method of operating an aerosol-generating device is also described.

Description

Technical Field

[0001] The present disclosure generally relates to an aerosol-generating device for heating an aerosol-generating substrate to generate an aerosol for inhalation by a user of the aerosol-generating device. The present disclosure is particularly suitable for portable (handheld) aerosol-generating devices. Such devices heat an aerosol-generating substrate (e.g., tobacco or other suitable material) by conduction, convection, and / or radiation, rather than by burning, to generate an aerosol for inhalation by the user. Background Art

[0002] In recent years, the use and popularity of risk-reducing or risk-modifying devices (also known as aerosol-generating devices or vapor-generating devices) has rapidly increased as an alternative to the use of traditional tobacco products. A variety of devices and systems are available that heat or increase the temperature of an aerosol-generating substance to produce an aerosol for inhalation by the user.

[0003] A commonly used risk reduction or risk modification device is a heated substrate aerosol-generating device, or so-called heat-not-burn device. This type of device generates an aerosol or vapor by heating an aerosol-generating substrate to a temperature typically in the range of 150°C to 300°C. Heating the aerosol-generating substrate to a temperature within this range without burning or combusting the aerosol-generating substrate produces a vapor that typically cools and condenses to form an aerosol that is inhaled by the user of the device.

[0004] Currently available aerosol-generating devices can use one of several different methods to provide heat to the aerosol-generating substrate. One such method employs an induction heating system. In such devices, an induction coil is provided within the device, along with an inductively heatable susceptor to heat the aerosol-generating substrate. When a user activates the device, electrical energy is supplied to the induction coil, which in turn generates an alternating electromagnetic field. The susceptor couples with the electromagnetic field and generates heat, which is transferred to the aerosol-generating substrate, for example, by conduction. When the aerosol-generating substrate is heated, an aerosol is generated.

[0005] Another heating method uses a resistive heating system. In such devices, a resistive heating element is provided to heat the aerosol-generating substrate. When the user activates the device, electrical energy is supplied to the resistive heating element, which in turn generates heat. This heat is transferred to the aerosol-generating substrate, for example, by conduction, and an aerosol is generated when the aerosol-generating substrate is heated.

[0006] In most such aerosol-generating devices, the heater operates in a predetermined manner when commanded to start, for example, in response to a user pressing a start button or in response to the device determining, using an airflow sensor, that the user has drawn a puff through the device. The heater typically operates for a predetermined session duration, which can be measured by a preset time (e.g., 4.5 minutes) or by a preselected number of puffs. The session time or the preselected number of puffs is selected with the goal of depleting all or substantially all of the aerosol-generating substrate within the consumable.

[0007] Typically, there may be some variation between different types of consumables, and even between different batches of the same type of consumables, for example due to manufacturing tolerances. This can result in a session terminating even though some usable aerosol-generating substrate remains in the consumable, which can be frustrating for the user. Alternatively, this can result in the aerosol-generating device continuing to heat the consumable even though all of the aerosol-generating substrate in the consumable has been consumed. This can result in an unpleasant end to the user's session (e.g., a poor taste) and can increase the likelihood of the consumable burning within the heating chamber. The present invention aims to alleviate one or more of the above-mentioned issues. Summary of the Invention

[0008] According to a first aspect of the present invention, there is provided an aerosol generating device comprising:

[0009] a heating chamber configured to receive a consumable including an aerosol-generating substrate;

[0010] a heating assembly operable to supply heat to the aerosol-generating substrate during a usage session; and

[0011] Controller;

[0012] The controller is operable to:

[0013] monitoring an observable quantity indicative of the moisture content of the aerosol-generating substrate during the usage session; and

[0014] An indication of the moisture content of the aerosol-generating substrate is progressively provided to the user during the usage session.

[0015] Consumables suitable for use with an aerosol-generating device typically have a certain moisture content when new. This moisture content is depleted by heating, so that used consumables typically have a much lower moisture content and may have little or no remaining moisture content. Therefore, the amount of moisture within the unheated consumable is indicative of the expected session length of the consumable. Therefore, progressively displaying an indication of the moisture content of the aerosol-generating substrate within the consumable to the user throughout a session can provide the user with an indication of the likely remaining session length and a visual representation of the depletion status of the aerosol-generating substrate.

[0016] The controller may be operable to select a duration for each usage session by using the monitored observable to determine when to terminate the session. Since moisture content indicates the expected session length, using the monitored observable to select a duration for each usage session may result in a more accurate session length tailored for each session.

[0017] The controller may be operable to terminate the session when the monitored observable indicates that the moisture content of the aerosol-generating substrate is at or below a first predetermined threshold. The first predetermined threshold may be a moisture content in the range of 1% to 6%, for example 5%.

[0018] The controller may be operable to measure an initial value of an observable upon insertion of the consumable into the heating chamber before heating begins. The initial value of the observable may therefore indicate the initial moisture content of the aerosol-generating substrate. The controller may be further operable to compare the measured initial observable with a further predetermined threshold. The controller may be operable to prevent operation of the heating assembly if the measured initial value of the observable is less than or equal to the further predetermined threshold (which may be the same as the first predetermined threshold). Alternatively, the controller may be operable to cause operation of the heating assembly only if the measured initial value of the observable equals or exceeds the further predetermined threshold (which may be a value of the observable representing an expected minimum initial moisture content). An unexpectedly low initial moisture content (i.e., a measured initial value of the observable indicating a moisture content below the expected minimum initial moisture content) may indicate that the consumable has already been heated. Therefore, comparing the measured initial observable with the further predetermined threshold may allow the aerosol-generating device to prevent further heating of the consumable after it has already been heated.

[0019] The controller may be operable to generate an indication that the end of the session is imminent. This indication may be provided to the user in addition to the step-by-step indication of moisture content provided throughout the session. The indication that the end of the session is imminent may be provided when the monitored observable indicates that the moisture content of the aerosol-generating substrate is at or below a second predetermined threshold, wherein the second predetermined threshold is reached before the first predetermined threshold. The second predetermined threshold may be in the range of 8% to 3%, 7% to 5%, or 6% to 5%. The second predetermined threshold may be equal to an estimated remaining session duration, such as 10%, 15%, or 20% (e.g., 30 seconds, 45 seconds, or 1 minute) of the remaining session duration.

[0020] The observable quantity may be monitored periodically throughout the usage session. For example, the observable quantity may be measured every 5 ms to 100 ms or every 10 ms to 50 ms.

[0021] The aerosol-generating device may further comprise a monitoring circuit having a predetermined time constant, wherein the observable quantity is a time delay associated with the monitoring circuit.

[0022] The time constant τ (tau) of a circuit is a parameter that characterizes the circuit's response to a step input. For example, in an RC circuit consisting of a single resistor and capacitor, the time constant τ (in seconds) = RC, where R is the resistance (in ohms) and C is the capacitance (in farads).

[0023] The consumable has a non-zero capacitance such that introducing the consumable into a monitoring circuit having a known time constant will cause the capacitance of the circuit to change, and therefore the time constant of the circuit to change. The consumable does not need to be in physical contact with the monitoring circuit to affect the capacitance of the circuit.

[0024] The capacitance of the consumable depends (at least in part) on the moisture content of the consumable. Because the time constant of the monitoring circuit varies with the capacitance, the time constant of the monitoring circuit represents an observable quantity indicative of the moisture content of the consumable present in the heating chamber of the aerosol-forming device. Thus, by monitoring the changes in the time constant of a monitoring circuit having a known time constant, changes in the moisture content of the consumable over the course of a session can be observed.

[0025] The monitoring circuit may include an RC circuit having a predetermined resistance and capacitance. An RC circuit has a simple and low-cost construction, and the time constant of such a circuit is computationally easy to measure. It should be understood that the wiring of the circuit necessarily has a certain capacitance, and therefore, the use of an RC circuit does not necessarily imply the presence of a capacitor.

[0026] The controller may be operable to supply a signal to an input of the monitoring circuit and receive a modified signal from an output of the monitoring circuit.The controller may be operable to determine the time delay based on the modified signal.

[0027] Observables may include rise and / or fall times associated with a signal. As used herein, the term "rise time" refers to the time (in seconds) for a signal (e.g., voltage) to change from a specified low value to a specified high value. Similarly, the term "fall time" refers to the time it takes for a signal to change from a specified high value to a specified low value. Thus, the controller may be operable to monitor changes in the rise and / or fall times, rather than monitoring the time constants themselves. The relative change in rise time between a state in which the consumable is present in the heating chamber and a state in which the consumable is not present in the heating chamber may be greater than the relative change between a known time constant of the monitoring circuit and the time constant that is changed due to the presence of the consumable. Thus, utilizing the rise and / or fall times may improve the accuracy of the determination.

[0028] The signal input to the monitoring circuit may include a voltage pulse, such as a square wave. The controller may be operable to periodically input the signal to the monitoring circuit. Using a sharp-edged signal (such as a pulse) may make it easier to observe the rise and / or fall times.

[0029] A monitoring circuit (e.g., an RC circuit) may be electrically connected to the heating circuit of the heating assembly. The change in the time constant of the monitoring circuit is typically small, particularly when the consumable is not in physical contact with the monitoring circuit. The present inventors have discovered that electrically connecting the monitoring circuit to the heating circuit of the aerosol-forming device increases the magnitude of the change in the time constant and, therefore, increases the sensitivity of the detection. Because the heating circuit is necessarily provided in the aerosol-forming device, this increased sensitivity does not come at the expense of increased complexity or additional manufacturing expense.

[0030] Measurements can be taken during a heating session; however, preferably, they are not taken at exactly the same time as the heater power pulses. Thus, the measurement of the observable can be timed to fall between heating pulses, and / or the heating assembly can be turned off while the observable is being monitored. This can reduce the likelihood that the voltage supplied to the heating assembly will damage the monitoring circuitry and / or can improve monitoring accuracy by reducing interference in the monitoring signal. For example, the observable can be measured every 5 ms to 100 ms or every 10 ms to 50 ms.

[0031] The aerosol generating device may be capable of switching between a heating mode, in which a voltage is supplied to the heating circuit, and a time delay monitoring mode, in which a signal is supplied to the monitoring circuit. When the aerosol generating device is in the time delay monitoring mode, the controller may be operable to determine the moisture content of the consumable product using only the time delay associated with the monitoring circuit. This may prevent damage to the monitoring circuit when a voltage is supplied to the heating circuit in the heating mode. The aerosol generating device may include a first switch that can be closed in the time delay monitoring mode and opened in the heating mode, and a second switch that can be closed in the heating mode and opened in the time delay monitoring mode.

[0032] The heating circuit may include a resistive heater, such as a resistive wire or a thin film heater.

[0033] The heating chamber can be substantially cup-shaped and can have a first open end operable to receive the consumable product. For example, the heating chamber can include a substantially cylindrical sidewall that is open at a first end, thereby defining the first open end, and closed at a second end, thereby defining a base of the heating chamber. The resistive heater can be external to the heating chamber and can be wrapped around the heating chamber.

[0034] The aerosol-generating device may further include a user interface having an output display, wherein the aerosol-generating device is operable to provide step-by-step instructions to the user using the display. The step-by-step instructions may be provided to the user in any suitable manner. For example, the display may include one or more lighting elements, such as LEDs, and the lighting elements may be initially illuminated at the beginning of a session and may be gradually turned off as the session progresses to provide a visual indication of the monitored moisture content. In an alternative example, the output display may include a display screen, and a graphical representation may be provided to the user via the display screen. Thus, the step-by-step instructions may allow the user to visually observe the depth of consumption of the consumable product.

[0035] According to a second aspect of the present invention, there is provided a method of operating an aerosol-generating device, the aerosol-generating device comprising:

[0036] a heating chamber configured to receive a consumable including an aerosol-generating article;

[0037] a heating assembly operable to supply heat to the aerosol-generating substrate during a usage session; and,

[0038] Controller;

[0039] The method includes:

[0040] monitoring an observable quantity indicative of the moisture content of the aerosol-generating substrate during the usage session; and

[0041] An indication of the moisture content of the aerosol-generating substrate is progressively provided to the user during the usage session.

[0042] The method may further include using the monitored observable to determine when to terminate the session.

[0043] The method may further include providing an indication to the user that the end of the session is imminent.

[0044] The method may further comprise measuring an initial value of the monitored observable quantity before commencing heating, and the controller comparing the measured initial value with a further predetermined threshold value.The controller may use the comparison to determine whether to commence heating.

[0045] The method may be implemented in the aerosol-generating device of the first aspect of the invention, and may further comprise any optional features of the first aspect of the invention.

[0046] Unless expressly stated otherwise, features of the above aspects of the invention may be combined in any order, and with features selected from the specification. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings, in which:

[0048] Figure 1 is a diagrammatic cross-sectional view of an aerosol-generating system comprising an aerosol-generating device and a consumable positioned in a heating chamber of the aerosol-generating device;

[0049] Figure 2 is suitable for Figure 1 Schematic representation of a thin film heater used in an aerosol generating device;

[0050] Figure 3 Shown wrapped around the heating chamber Figure 2 Thin film heater;

[0051] Figure 4 The change of measured observables indicative of moisture content over time is schematically shown;

[0052] Figure 5 Demonstrates suitability for use in first time delay monitoring mode and second heating mode Figure 1 An exemplary monitoring circuit in an aerosol-generating device;

[0053] Figure 6schematically illustrates a time delay monitoring method; and

[0054] Figure 7 showing the changes in rise and / or fall times measured before, during, and after the consumable is inserted into the heating chamber;

[0055] Figure 8 showing the changes in rise and / or fall times measured before, during, and after insertion of a heated consumable into the heating chamber; and

[0056] Figure 9 yes Figure 7 A close-up of the area of ​​the graph shown. DETAILED DESCRIPTION

[0057] First reference Figure 1 , diagrammatically illustrates an example of an aerosol-generating system 1. The aerosol-generating system 1 includes an aerosol-generating device 10 and a consumable product 100 (also referred to herein as an aerosol-generating article) for use with the device 10. The aerosol-generating device 10 can have any shape that is sized and configured to fit the components described in the various embodiments set forth herein and to be comfortably held in a single hand by a user.

[0058] For convenience, Figure 1 The first end 14 of the aerosol generating device 10 shown at the bottom is described as the distal end, bottom end, base end or lower end of the aerosol generating device 10. Figure 1 The second end 16 of the aerosol-generating device 10 shown at the top of the aerosol-generating device 10 is described as the proximal end, top end, 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 facing downward and / or in a distal position relative to the user's mouth, and the second end 16 facing upward and / or in a proximal position relative to the user's mouth.

[0059] The aerosol-generating device 10 comprises a heating chamber 18. The heating chamber 18 defines an interior volume having a generally cylindrical cross-section in the form of a cavity 20. The cavity 20 of the heating chamber 18 is open towards the second end 16 of the aerosol-generating device 10. The heating chamber 18 has a longitudinal axis defining a longitudinal direction and is formed from a metallic material, such as stainless steel.

[0060] A heating assembly 15 including a heating element 22 is positioned proximate the heating chamber 18 and is operable to provide heat to the heating chamber. The heating element 22 is included within a heating circuit 40 that is electrically connected to the controller 24.

[0061] The aerosol-generating device 10 further includes a power source 26 (e.g., which may be one or more rechargeable batteries). A controller 24 couples the power source 26 to the heating element 22. The controller 24 may also be connected to a user interface 23, which may include inputs (e.g., a power button for receiving commands from a user) and / or outputs (e.g., an indicator light, a display, or an audible or vibrating alarm for providing information to the user). The controller 24 may also interface with an antenna 25 for wireless communication with a remote device (e.g., a user's smartphone), which may be used for input and output, as well as for relaying data between the aerosol-generating device 10 and its manufacturer.

[0062] The heating chamber 18, and in particular 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 substrate 102. The aerosol-generating article 100 is a disposable and replaceable article (also referred to as a "consumable") that may, for example, contain tobacco as the aerosol-generating substrate 102. The aerosol-generating article 100 has a proximal end 104 (or mouth end) and a distal end 106. The distal end 106 is inserted into the heating chamber 18 of the aerosol-generating device 10 so that at least the aerosol-generating substrate 102 is contained within the heating chamber 18. The aerosol-generating article 100 further comprises a mouthpiece segment 108 positioned downstream of the aerosol-generating substrate 102. At least a portion of the mouthpiece segment 108 protrudes from the heating chamber 18, making the proximal end 104 of the aerosol-generating article 100 accessible for bringing to the user's mouth. When the aerosol-generating device 10 applies heat to the aerosol-generating article 100, heated vapor is expelled from the aerosol-generating substrate 102. When the user's inhalation draws air toward the proximal end 104 of the aerosol-generating article 100, the vapor cools and condenses as it passes through the mouthpiece segment 108 to form an aerosol having properties suitable for inhalation. The mouthpiece segment 108 may further include a filter (not shown) to remove particles or droplets exceeding a certain size from the airflow.

[0063] The aerosol-generating substrate 102 and the mouthpiece segment 108 are coaxially aligned and arranged inside a wrapper 110 (e.g., a paper wrapper) to hold the components in place to form the rod-shaped aerosol-generating article 100. The wrapper 110 typically does not cover the ends 104, 106 of the aerosol-generating article 100 so that air can flow through the aerosol-generating article 100 from the distal end 106 to the proximal end 104.

[0064] The aerosol-generating substrate 102 can be provided as a solid or paste-type material in shredded, pelletized, powdered, granular, strip, or sheet form, optionally in combination thereof. The aerosol-generating substrate can include, for example, tobacco in a dried or cured form, in some cases with additional ingredients for flavoring or to create a smoother or otherwise more pleasurable experience. In some examples, the aerosol-generating substrate 102 (e.g., tobacco) can be treated with a vaporizer. The vaporizer can improve the generation of vapor from the aerosol substrate. For example, the vaporizer can include a polyol (e.g., glycerol) or a glycol (e.g., propylene glycol). In some cases, the aerosol-generating substrate may not contain tobacco or even nicotine, but may contain natural or artificially derived ingredients for flavoring, volatilization, improved smoothness, and / or other pleasurable effects. The aerosol substrate 12 (e.g., tobacco) can include one or more humectants, such as glycol(s), to retain moisture.

[0065] Before use, the aerosol-generating substrate 102 has an initial moisture content, which may depend on its design, shape, packaging, type, flavor, etc. As used herein, "moisture content" refers to the amount of water and any other humectants that may be present in the aerosol-generating substrate 102, and can be defined by the mass (e.g., weight water content), volume (e.g., volume water content), or any other measurable physical quantity of the aerosol-generating substrate. It should be understood that in practice, moisture content may vary slightly between consumables. Typically, the moisture content of the tobacco rod before use (i.e., initial moisture content) is a value of about 15%. After use, the moisture content of the tobacco rod typically drops to a value of about 5%.

[0066] In the illustrated embodiment of the present invention, the heating chamber 18 comprises a first open end 28 and a closed base 30 at a second end. That is, the heating chamber 18 is cup-shaped. This ensures that air drawn from the open end 28 is directed around the consumables toward the base 30, at which point the air is drawn through the aerosol-generating substrate 102.

[0067] As mentioned above about Figure 1 As described, the aerosol-generating device 10 comprises a heating chamber 18 configured to receive a consumable 100 comprising an aerosol-generating substrate 102; a heating assembly 15 configured to supply heat to the heating chamber 18; and a controller 24. The controller 24 is operable, inter alia, to monitor an observable value indicative of the moisture content of the aerosol-generating substrate during a usage session and to progressively provide an indication of the moisture content of the aerosol-generating substrate to a user during the usage session.

[0068] Figure 2 Shown for Figure 1An example of a heating element 22 in a heating circuit 40 of the type shown. The heating element 22 is a resistive heating element, specifically a thin film heater. The heating element comprises a heating track 32 embedded in a thin film and a pair of contacts 34, 36 allowing connection to a controller 24.

[0069] Figure 3 The heating chamber 18 of the aerosol generating device 10 is shown in more detail. The heating chamber 18 has a cylindrical side wall 38 connecting the first open end 28 and the closed base 30. Around the outer surface of the side wall 38 the heating element 22 is wrapped.

[0070] Figure 4 A diagram shows how a measured observable can change during a usage session. Figure 4 An initial state 400 of the aerosol-forming device is shown in which no consumable is present in the heating chamber. During this initial period, measurements of the observable indicate a moisture content of zero or approximately zero because no consumable is present in the heating chamber.

[0071] During a second time period 402, the consumable is inserted into the heating chamber. The measured value of the observable indicates a sharp increase in moisture content. Once the consumable is fully inserted, the first value of the measured observable, m1, can be considered to indicate the initial moisture content of the consumable. As described above, the first value of the measured observable, m1, can be equated to a moisture content within the aerosol-generating substrate of approximately 15%.

[0072] Heating of the consumable begins at a start time 404 after the consumable is inserted and continues for a session 406. During session 406, an observable value indicative of moisture content is measured and generally decreases throughout the session as water and / or humectant within the consumable vaporizes during heating. The session ends when the measured observable value reaches a second value m2, indicating that the water and / or humectant within the consumable has been substantially depleted. This does not necessarily mean that the moisture content is zero; rather, it means that the moisture content has fallen below a first predetermined threshold, below which the quality of the inhalation experience will be reduced. This threshold may be a moisture content of 6% or less, or 5% or less, or 4% or less, or, for example, lower.

[0073] Once the first predetermined threshold is reached, heating is stopped at time 408 , and thus the second value m2 of the measured observable indicative of residual moisture content remains constant during the post-session time period 410 .

[0074] To aid in monitoring observables, Figure 1The illustrated aerosol-generating device 10 further includes a monitoring circuit 50. The monitoring circuit may be included within the controller 24, or in signal communication with the controller 24. The monitoring circuit may be operable to monitor any observable quantity indicative of the moisture content of the aerosol-generating substrate. An example of such an observable quantity is a time delay associated with the monitoring circuit having a known time constant.

[0075] Now refer to Figure 5 , shows an exemplary monitoring circuit 50 and heating circuit 40 in greater detail. Monitoring circuit 50 includes a resistor R and an optional capacitor C, thereby forming an RC circuit. Monitoring circuit 50 includes an electrical input 52 and an electrical output 54 connected to microcontroller µC. It should be understood that microcontroller µC may be included within controller 24, or may be separate from controller 24 and under the command of controller 24.

[0076] The monitoring circuit 50 is Figure 5 The monitoring circuit 50 is shown as being connected to the heating circuit 40, and in particular to the contact 34 of the heating circuit 40. However, this is not strictly necessary, and the monitoring circuit 50 may be connected to another part of the heating assembly 15 (if desired) or to another part of the aerosol-forming device (such as the heating chamber 18).

[0077] Resistor R is connected between input 52 and output 54 and in parallel with capacitor C, which is connected to ground. The value of resistor R is in the range of 500 kΩ to 10 MΩ. Capacitor C is optional but, if present, helps clean up the signal.

[0078] The monitoring circuit 50 further includes a first switch 56 that is connected between the monitoring circuit 50 and the heating circuit 40, and specifically between the monitoring circuit 50 and the contact 34 of the heating track 32. When the first switch 56 is in the closed position, the monitoring circuit is electrically connected to the heating circuit 40. In this state, the aerosol-generating device 10 can be considered to be in the time-delay monitoring mode. When the first switch 56 is in the open position, the monitoring circuit 50 is not electrically connected to the heating circuit 40, so that no current can flow between the monitoring circuit 50 and the heating circuit 40.

[0079] The heating circuit 40 includes a second switch 42 positioned between the heating element 22 and an input voltage (e.g., supplied by the power supply 26 ); and a third switch 44 positioned between the heating element 22 and ground. When the second switch 42 and the third switch 44 are closed, the heating element 22 is electrically connected to the input voltage, such that voltage can be supplied to the heating element 22 to generate heat. In this state, the aerosol-generating device can be considered to be in a heating mode. When the second switch 42 and the third switch 44 are open, the heating element 22 is disconnected from the input voltage and cannot generate heat.

[0080] The aerosol generating device may be in both the heating mode and the time delay monitoring mode simultaneously, such that all three switches 56, 42, 44 are closed simultaneously. However, in this example, the aerosol generating device is operable to switch between the time delay monitoring mode and the heating mode such that time delay monitoring does not occur during heating.

[0081] Now refer to Figure 6 The operation of the aerosol-generating device 10 in the time-delay monitoring mode will now be described. In the time-delay monitoring mode, the microcontroller µC is operable to send a signal 60 to the input 52 of the monitoring circuit 50 (e.g., from a pin labeled "send"). The signal 60 is a voltage pulse, such as a square wave defined by a low value 62 and a high value 64, and may repeat periodically.

[0082] The signal passes through monitoring circuit 50 and also through heating circuit 40 because switch 56 is closed in time-delay monitoring mode. Microcontroller µC receives the signal from output 54 (e.g., at the pin labeled "return"); however, the received signal is altered due to capacitance in the system. This alteration is characterized by a rise time d, which is the time it takes for the signal to change from a low value 62 to a high value 64, and a fall time, which is the time it takes for the signal to return from a high value 64 to a low value 62. In the original signal, these changes are virtually instantaneous, but in the received signal, there is a delay as the signal rises from low to high and as it falls from high to low. The rise time is proportional to the circuit's time constant. Similarly, the fall time is also proportional to the circuit's time constant.

[0083] Figure 6 A graph 70 is included that plots rise and fall times 72 against time 74, allowing for perception of changes in rise and fall times over time. It can be seen that the rise time d1 at a first time 76 is less than the rise time d2 at a second time 78. This indicates that the capacitance in the system has changed between the first and second times. Specifically, the capacitance in the system has increased between the first and second times 76 and 78.

[0084] Figure 7 Shows how to use Figure 6 The variation in rise and / or fall times shown is used to determine the moisture content of the consumable 100 within the heating chamber 18 of the aerosol-generating device 10 . Figure 7 Included is a graph that plots measured rise and fall times 72 (in this example, rise and fall times are represented by the propagation time of a signal from input to output) relative to time 74 between an initial time t0 and an end time t5.

[0085] During a first time period 82 between time t0 and time t1, a reference transmission time (e.g., average rise and fall times) is a first reference time a1. During this time period, no consumables are present in the heating chamber. Therefore, the rise and fall times experienced by the signal during this time period indicate the time constant τ of the monitoring circuit in the absence of any consumables and can be considered a predetermined time constant.

[0086] At time t1, the measured rise and fall times increase, and the third reference time a3 is averaged over a second time period 84 between time t1 and time t2. The increase in rise and fall times indicates that the capacitance of the system has increased, and therefore that the time constant τ of the monitoring circuit has changed, and in particular, increased. During this time period, the consumable is being inserted into the heating chamber 18 (i.e., is in the process of being inserted and is not yet fully inserted, but rather is partially inserted and / or in close proximity to the heating chamber). The increase in capacitance during this time period is due to the presence of the consumable 100 near and / or partially within the cavity of the heating chamber, and potentially also due to contact between the consumable and a user's finger.

[0087] At time t2, the measured rise and fall times decrease, and the second reference time a2 is averaged during a third time period 86 between time t2 and time t3. The decrease in rise and fall times indicates that the capacitance of the system has decreased, and therefore indicates that the time constant τ of the monitoring circuit has changed, and in particular has decreased. However, it should be noted that the value a2>a1 means that the capacitance in the system, and therefore the time constant of the system, is greater than the predetermined time constant τ of the monitoring circuit in the absence of any consumables. During this time period, the consumable 100 is present in the heating chamber 18 of the aerosol-generating device. The consumable is heated during this time, and therefore the third time period 86 can also be considered a puffing session.

[0088] Figure 9A close-up of the measurements taken during the third time period 86 is shown in FIG. 1. It can be seen that although the rise and fall times measured during the third time period 86 are averaged over the second reference time a2, in fact, the measured rise and fall times decrease overall by 94% during the entire third time period 86. This is because, as discussed above with respect to Figure 4 As discussed, the rise and fall times are indicative of the moisture content of the consumable within the heating chamber, and the moisture content decreases over the course of a session as the water and / or humectant within the aerosol-forming substrate is depleted.

[0089] At time t3, the rise and fall times increase, and additional rise / fall times are averaged during a fourth time period 88 between time t3 and time t4. Fourth time period 88 represents the inverse of second time period 84, as consumables are being removed from the heating chamber during the fourth time period. Therefore, the average rise and fall times during the fourth time period are similar to and approximately the same as the average rise and fall times a3 during the second time period.

[0090] Similarly, the average rise and fall times during the fifth time period 90 between times t4 and t5 are similar to and substantially the same as the first average rise and fall times a1 during the first time period, indicating that the consumable is no longer present in the heating chamber.

[0091] Thus, changes in the time constant of the monitoring circuit (eg, measured using changes in time delays, such as changes in rise and / or fall times as discussed above) can be used to monitor the moisture content of consumables present in the heating chamber.

[0092] In one example, the controller is operable to begin monitoring the observable only after the rod is inserted and heating has begun. A state machine, scheduler, timer interrupt, or watchdog timer disconnects the heater and connects the measurement line every 10 to 50 ms to periodically acquire measurements of the observable. The acquired data can be stored in memory (internal or external to the controller), and signal processing of the stored data can be used to provide an indication of moisture level depletion.

[0093] The aerosol-generating device 10 is configured to use the monitored observable to progressively display an indication of the moisture content of the consumable to the user of the device throughout a session. This indication may be displayed to the user on the user interface 23 of the aerosol-generating device and / or may be displayed on a connected device (such as the user's smartphone), for example, via an application paired with the aerosol-generating device. This indication may progressively provide the user with a visual representation of the depth of consumption of the consumable throughout a session, such that at any given time, the user has an instantaneous representation of how much aerosol-generating substrate has been consumed.

[0094] For comparison, Figure 8 The change in rise and / or fall times when a consumable that has already been heated is inserted into a heating chamber of an aerosol-forming device is illustrated. During a first time period 96 and during a third time period 97, no consumable is present in the heating chamber. However, during a second time period 98, a consumable 100' is inserted into the heating chamber. The consumable 100' has been heated so that the measured observable indicative of its moisture content is substantially at or below the observable m2 indicative of the residual moisture content. Therefore, the controller of the aerosol-generating device may be able to use the measured observable to determine that the consumable inserted into the heating chamber has been used. In this case, the controller may prevent further heating of the already heated stick. For example, the controller may prevent operation of the heating circuit in this case.

[0095] While exemplary embodiments have been described in the preceding paragraphs, it should be understood that various modifications may be made to these embodiments without departing from the scope of the appended claims. For example, while the present invention has been primarily described in conjunction with resistive heating assemblies, the present invention may find utility in conjunction with other types of heating assemblies, such as induction heating assemblies. Therefore, the breadth and scope of the claims should not be limited to the exemplary embodiments described above.

Claims

1. An aerosol generating device (10), comprising: a heating chamber (18) configured to receive a consumable (100) comprising an aerosol-generating substrate (102); a heating assembly operable to supply heat to the aerosol-generating substrate during a usage session; as well as Controller (24); The controller is operable to: monitoring an observable quantity indicative of the moisture content of the aerosol-generating substrate during the usage session; and An indication of the moisture content of the aerosol-generating substrate is progressively provided to the user during the usage session.

2. The aerosol generating device according to claim 1, wherein: The controller is operable to select a duration for each usage session by: The monitored observables are used to determine when to terminate the session.

3. The aerosol generating device according to claim 1 or claim 2, wherein: The controller is operable to terminate the session when the monitored observable indicates that the moisture content of the aerosol-generating substrate is at or below a first predetermined threshold.

4. An aerosol-generating device according to any preceding claim, wherein The controller is operable to generate an indication that the end of a session is imminent when the monitored observable indicates that the moisture content of the aerosol-generating substrate is at or below a second predetermined threshold, wherein the second predetermined threshold is reached before the first predetermined threshold.

5. An aerosol-generating device according to any preceding claim, wherein The observable is monitored periodically throughout the usage session.

6. An aerosol-generating device as claimed in any preceding claim, further comprising a monitoring circuit (50) having a predetermined time constant, wherein The observable is a time delay associated with the monitoring circuit.

7. The aerosol generating device according to claim 6, wherein: The controller (24) is operable to supply a signal to an input of the monitoring circuit (50) and receive a modified signal from an output of the monitoring circuit, the controller being operable to determine the time delay based on the modified signal.

8. The aerosol generating device according to claim 7, wherein: The monitoring circuit (50) includes an RC circuit having a predetermined resistance and capacitance, and the observable quantity is a rise and / or fall time associated with the signal.

9. The aerosol generating device according to claim 8, wherein: The RC circuit is electrically connected to the heating circuit (40) of the heating assembly.

10. An aerosol-generating device according to any preceding claim, wherein While the observable is being monitored, the heating assembly is turned off.

11. The aerosol generating device according to any one of claims 6 to 9, wherein: The aerosol generating device (10) is switchable between a heating mode and a time delay monitoring mode, wherein a voltage is supplied to the heating component in the heating mode and a signal is supplied to the monitoring circuit (50) in the time delay monitoring mode.

12. An aerosol generating device as claimed in claim 11, further comprising a first switch (56) and a second switch (42), the first switch being closed in the time delay monitoring mode and being open in the heating mode, the second switch being closed in the heating mode and being open in the time delay monitoring mode.

13. An aerosol-generating device according to any preceding claim, wherein The heating circuit comprises a resistive heater (22), and preferably a thin film heater.

14. An aerosol-generating device as claimed in any preceding claim, further comprising a user interface (23) having an output display, wherein The aerosol-generating device is operable to provide the instructions to the user step by step using the display.

15. An aerosol-generating device according to any preceding claim, wherein The controller is further operable to: measuring an initial value of the observable, the initial value being indicative of an initial moisture content; comparing the measured initial value with a further predetermined threshold, and A determination is made based on the comparison whether activation of the heating component is permitted.

16. The aerosol generating device according to claim 15, wherein: The controller is operable to prevent operation of the heating assembly if the measured initial value of the observable is at or below the further predetermined threshold.

17. The aerosol generating device according to claim 15 or 16, wherein: The additional predetermined threshold is the same as the first predetermined threshold or the second predetermined threshold.

18. A method of operating an aerosol-generating device, the aerosol-generating device comprising: a heating chamber (18) configured to receive a consumable including an aerosol-generating article; a heating assembly operable to supply heat to the aerosol-generating substrate during a usage session; Controller (24); The method includes: monitoring an observable quantity indicative of the moisture content of the aerosol-generating substrate during the usage session; and An indication of the moisture content of the aerosol-generating substrate is progressively provided to the user during the usage session.

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