Dryer heater detection for aerosol generating systems

Abstract

The present invention includes adjusting the power supply to a heating element during a plurality of individual heating cycles, determining an electrical resistance ratio ΔR / Δt of the heating element at predetermined time intervals during the heating cycles, and calculating a moving average value s of the electrical resistance ratio ΔR / Δt of the heating element during n preceding heating cycles. n wherein n is an integer greater than 1; comparing an electrical resistance ratio ΔR / Δt of the heating element to the calculated moving average value; determining a fault when the electrical resistance ratio ΔR / Δt is greater than the moving average value by more than a threshold value; and controlling the supply of power to the heating element based on whether a fault is determined in the heating element.

Description

[Technical field]

[0001] FIELD OF THE DISCLOSURE The present disclosure relates to a method for operating a heating element in an electrically operated aerosol generating system, and in particular to the detection of undesirable heater conditions in an electrically heated aerosol generating system.

[0002] In an aerosol generating system, a liquid aerosol-forming substrate may be delivered from a liquid reservoir to an electric heating element. As it is heated to a target temperature, the aerosol-generating substrate vaporizes to form an aerosol. The liquid substrate may be delivered to the heating element via a capillary component. When the amount of aerosol-generating substrate in the capillary component is depleted, the heating element may enter a so-called dry state. In such a dry state, the heating element may easily overheat. Overheating of the heating element may affect the quality of the aerosol. Furthermore, overheating of the heating element may lead to the destruction of the heating element.

[0003] Efforts have been made to detect the dry state of heating elements used in electrically operated aerosol generating systems. However, many of these techniques for detecting the depletion of the aerosol generating substrate still require a substantial increase in heater temperature to detect the resulting change in electrical resistance. In addition, some of these methods require detection of the initial heater resistance. However, the absolute resistance of a heating element is typically less than 1 ohm, and the resistance change of a heating element entering a dry state may be only a few milliohms. Such small changes in absolute resistance may be difficult to identify in an aerosol generating system.

[0004] It would therefore be desirable to provide a method that allows for reliable detection of a fault condition of a heating element. It would further be desirable to provide a method that allows for reliable detection of a fault condition of a heating element and that can be used with a variety of types of heating elements. It would further be desirable to provide a method of operation of a heating element that prevents operation of the heating element before a fault condition is reached.

[0005] According to the present invention, a method for controlling the power supply to a heating element in an electrically operated aerosol generating system is provided. The method includes the steps of adjusting the power supply to the heating element during a number of separate heating cycles, determining an electrical resistance ratio ΔR / Δt of the heating element at predetermined time intervals, and calculating a moving average value sn of the electrical resistance ratio ΔR / Δt of the heating element during n preceding heating cycles, where n is an integer greater than 1. The method further includes the steps of comparing the electrical resistance ratio ΔR / Δt of the heating element to the calculated moving average value, and determining a fault when the electrical resistance ratio ΔR / Δt is greater than the moving average value sn by more than a threshold value. The power supplied to the heating element is controlled based on whether a fault in the heating element is determined.

[0006] For a given power supply to the heating element, the maximum temperature at the heating element is limited by the amount of aerosol-forming substrate available. This is due to the latent heat of vaporization of the aerosol-forming substrate. Thus, the maximum electrical resistance at the heating element can be related to the amount of aerosol-forming substrate available at the heating element. For example, a lack of aerosol-forming substrate can result in a significant increase in the maximum electrical resistance detected over multiple consecutive heating cycles. Thus, an empty cartridge can be detected when the increase in maximum electrical resistance from one puff to the next exceeds a threshold value.

[0007] However, the supply of aerosol-forming substrate in the heating element may decrease stepwise over the life of the cartridge. As the aerosol-forming substrate begins to run out, the maximum resistance of the heating element may also increase gradually over successive puffs. Thus, during a malfunction, there may be no substantial difference in the maximum resistance detected between two successive puffs. This means that an empty cartridge may not be detected quickly.

[0008] In dry conditions, heating elements can reach temperatures in excess of 1000 degrees Celsius. This typically leads to permanent destruction of the heating element, such as filament breakage for mesh heaters or immediate breakage of ceramic heaters. Apart from destruction of the heating element, undesirable aerosol components can be formed.

[0009] A dry wick condition can be caused by a depleted cartridge, resulting in insufficient liquid being available to be delivered to the heating element. A dry wick condition can also be caused by other circumstances. A dry wick condition can result from mispositioning of the aerosol generating device, causing the supply of liquid substrate to be stopped or slowed down. A dry wick can also be caused by a user overdrawing. Regardless of the cause of the dry wick condition, operation of the heating element in a dry wick condition should be prevented. Therefore, the present invention is configured to alert the user to the occurrence of a potential dry wick condition. If the dry wick condition is caused by a depleted cartridge, operation should typically only be resumed after replacement or refilling of the cartridge. For other causes, such as mispositioning of the aerosol generating device, operation may be resumed after a temporary locking of the aerosol generating device.

[0010] The correlation between the temperature and resistance of a heating element can be expressed by the following equation:

[0011]

number

[0012] The nominal resistance and alpha value α depend on the type of heating element used. Typically used heating elements have a nominal resistance that can be very low, even below 1 ohm.

[0013] The alpha value for the mesh heater may be about 0.00119 and its nominal resistance may be about 0.58 ohms. The alpha value for the ceramic heater may be about 0.00016 and its nominal resistance may be about 0.98 ohms. The alpha value for the wick-coil heater may be about 0.00013 and its nominal resistance may be about 1.6 ohms.

[0014] While all heating elements exhibit an increase in electrical resistance when entering a dry wick state, the absolute increase in electrical resistance may be very small, only about 0.006 ohms. Therefore, detection of a dry wick state based on a change in absolute resistance may be hindered by a poor electrical connection. Such a poor electrical connection may lead to a similar or even higher change in overall resistance, causing a false trigger to lock up the system unnecessarily.

[0015] Surprisingly, it has been found that reliable detection of the dry core condition can be performed by monitoring the electrical resistance ratio ΔR / Δt of the heating element at predetermined time intervals.

[0016] More specifically, it has been found that the electrical resistance ratio ΔR / Δt of a given heating element exhibits a characteristic increase immediately before or upon entering a dry wick state. Since the changes in the electrical resistance ratio ΔR / Δt of a given heating element can be very small, statistical methods are necessary to identify statistically significant changes in the electrical resistance ratio ΔR / Δt. One advantage of the proposed method is that the current parameter of a given heating element is repeatedly determined and compared with previous values ​​of this parameter. Hence, the performance of the heating element is continuously compared with its previous performance. Hence, the system is continuously compared with itself. This makes it possible to reliably determine if the heating element starts to move away from the desired operating range. Hence, manufacturing differences between structurally identical heating elements are effectively compensated for.

[0017] The following formula has been found to be useful in determining whether a given heating element is about to enter or has entered a dry wick state.

[0018]

number

[0019] In this formula, ΔR / Δt is the electrical resistance ratio, sn is the running average of the previous n values ​​of the electrical resistance ratio, σ is the standard deviation calculated based on the number of previous values ​​of the electrical resistance ratio, and A is a number empirically determined for each type of heating element.

[0020] The standard deviation σ is calculated based on a limited number of previous values ​​of the electrical resistance ratio. Therefore, this value is not actually a true statistical measure of the standard deviation (the true standard deviation can only be determined at the end of the heating cycle taking into account all measurements). The standard deviation σ may also be described as an average value for calculating the weighting of each sample. This average value is rather a moving average of a certain length and is not a true sample average. In the context of the present invention, the deviation σ may be considered as a standard deviation based on exponential smoothing (EWMSD). At the beginning of the sampling period, the weight of each sample decays exponentially. This is particularly useful in the heating of an aerosol-forming substrate, since it has been found that at the beginning of the heating process the heating process is not yet uniform and the individual deviations are quite high.

[0021] One of the goals of using this average is to minimize data usage and computation time. This method reduces accuracy and statistical validity, but improves overall performance. Because a reduced number of values ​​needs to be calculated, the monitoring program can run for longer periods at a fast sampling rate.

[0022] As can be seen from equation (2), the method of the present invention involves determining a statistical measure of the standard deviation σ of the electrical resistance ratios, which is referred to as σ in equation (2).

[0023] Additionally, a moving average sn of the previous n values ​​is determined. A statistically significant increase in the electrical resistance ratio ΔR / Δt is detected by comparing the new value of the electrical resistance ratio with the moving average sn of the previous n values ​​of the electrical resistance ratio using equation (2).

[0024] If this difference is higher than the product of the calculated standard deviation σ and a predefined constant value A determined empirically, a statistically significant increase is determined. In such a case, the system is configured to take certain measures to further ensure safe operation. The system may be triggered to enter a lockout mode and prevent the system from continuing the user experience. Alternatively, the system may be triggered to recheck to ensure that the system has entered the drying stage.

[0025] The recheck process is useful to prevent a single spike value from unduly preventing operation of the system. However, if a statistical increase in the electrical resistance ratio is rechecked, the system may then enter a lockout mode in which further operation is prevented. Operation can then be resumed only if the cause of the lockout is resolved. Typically, the user will need to refill or replace the spent cartridge.

[0026] The present invention may generally be used with any type of heating element by which a liquid aerosol-forming substrate is heated. The heating element may include a mesh heater, a wick-coil type heater, or a ceramic heater.

[0027] Wick-coil heaters are readily known in the prior art and essentially comprise a porous element in contact with a liquid reservoir. The liquid aerosol-forming substrate is moved via capillary action towards a portion of the porous element around which the heating coil is wrapped. In operation, heat generated by the heating coil is used to vaporize the liquid and ultimately form the aerosol.

[0028] For wick-coil heaters, the resistance increases steadily throughout the heating cycle, but then rises rapidly as the element enters a dry state.

[0029] A mesh heater may be, for example, an array of filaments arranged parallel to one another. The mesh may be woven or non-woven. The mesh may be formed using different types of weave or lattice structures. Alternatively, a conductive heating element may consist of an array of filaments or a weave of filaments. A mesh, array, or weave of conductive filaments may also be characterized by its ability to retain liquid.

[0030] The filaments of the heating element may be formed of any material having suitable electrical properties. Suitable materials include, but are not limited to, semiconductors such as doped ceramics, "conductive" ceramics (e.g., molybdenum disilicide, etc.), carbon, graphite, metals, alloys, and composites made of ceramic and metallic materials. Such composites may include doped or undoped ceramics. An example of a suitable doped ceramic includes doped silicon carbide. Examples of suitable metals include titanium, zirconium, tantalum, and platinum group metals.

[0031] The electrical resistance of the mesh, array or fabric of conductive filaments of the heating element may be between 0.3 ohms and 4 ohms. Preferably, the electrical resistance is 0.5 ohms or greater. More preferably, the electrical resistance of the mesh, array or fabric of conductive filaments is between 0.6 ohms and 0.8 ohms, and most preferably about 0.68 ohms.

[0032] For mesh heaters, it has been found that the maximum resistance is very consistent between puffs when the heating element is wet, and rises rapidly when the element is dry.

[0033] The ceramic heater may comprise any suitable ceramic material. The ceramic material may be a porous ceramic material. The capillary material may have any suitable capillarity and porosity for use with different liquid physical properties. The capillary material may be configured to transport the aerosol-forming substrate from the liquid reservoir.

[0034] Ceramic heaters may include resistive materials that form the heating portion of the heating element. Resistive materials may include semiconductors, such as doped ceramics, "conductive" ceramics (e.g., molybdenum disilicide, etc.), carbon, graphite, metals, alloys, and composites made of ceramic and metallic materials. Such composites may include doped or undoped ceramics. Examples of suitable doped ceramics include doped silicon carbide. Examples of suitable metals include titanium, zirconium, tantalum platinum, gold, and silver.

[0035] In the case of ceramic heaters, the resistance increases over a few puffs as the ceramic heating element begins to dry out. The resistance then decreases, but increases again significantly as the resistive heater portion begins to deform.

[0036] The method of the present invention has been successfully used to detect a dry wick condition at the beginning or end of the first dry puff for conventional mesh heaters, wick-coil heaters, and ceramic heaters. Hence, the method can be used for early detection of a system entering the dry stage.

[0037] Power may be supplied to the heating element continuously after activation of the system, or may be supplied intermittently, such as after every puff. Power may also be supplied to the heating element in a pulsed mode.

[0038] In pulse mode, power may be supplied to the heating element in the form of current pulses. The electrical circuit may be configured to monitor the electrical resistance of the heating element and to control the supply of power to the heating element, preferably in response to the electrical resistance of the heating element.

[0039] The number of pulses in a heating cycle may be selected as suitable for a given device. The number of pulses may be between 1 and 50 pulses per heating cycle. The number of pulses may be between 5 and 30 pulses per heating cycle. The number of pulses may be between 10 and 20 pulses per heating cycle.

[0040] In pulse mode, the heating elements may be operated in fixed power (FP) mode or fixed duty cycle (FDC). Fixed power mode has been identified as being most suitable for use in the present invention.

[0041] The term "duty cycle" as used herein refers to the amount of time a signal is on and the amount of time the signal is off. Duty cycles are given as a percentage. For example, a 60% duty cycle means that the signal is on 60% of the time and the signal is off 40% of the time.

[0042] For determining the moving average sn of the electrical resistance ratio, it is preferable to take into account fewer values ​​than when determining the standard deviation σ. The moving average sn may be determined taking into account the previous n values ​​of the electrical resistance ratio ΔR / Δt, n being in the range of 1 to 30. The moving average sn may be determined taking into account the previous n values ​​of the electrical resistance ratio ΔR / Δt, n being in the range of 5 to 20. The moving average sn may be determined taking into account the previous 10 values ​​of the electrical resistance ratio ΔR / Δt. This value may be called s10. By taking into account only a limited number of values ​​of the electrical resistance ratio, calculation power can be saved while a sufficient accuracy of the identification of dry cores is maintained.

[0043] The threshold for determining the fault may be determined from the standard deviation σ of the electrical resistance ratio ΔR / Δt. The standard deviation σ of the electrical resistance ratio ΔR / Δt may be determined as a moving average of the resistance ratio ΔR / Δt, taking into account m previous values ​​of the electrical resistance ratio ΔR / Δt, where m may be any predefined number. M may be 50, 30, or 10. The number of values ​​considered to determine the standard deviation σ may depend on the available computing power. The number of values ​​m used to determine the standard deviation σ may be greater than the number of values ​​n used to determine the moving average sn.

[0044] The threshold for determining a fault may be determined from the product of the standard deviation σ of the electrical resistance ratio ΔR / Δt and a constant value A. The constant value A may be empirically identified for each type of heating element used. The constant value A may be used to adjust the sensitivity of the detection method.

[0045] The smaller the constant value A, the lower the threshold and the more sensitive the dry wick detection. However, using too low a constant value A may compromise reliability, as increased sensitivity may cause false triggers or premature lockout. On the other hand, a constant value A that is too high may result in delayed detection of a dry wick condition or may prevent detection altogether.

[0046] An optimum constant value A is preferably determined for each type of heating element used.

[0047] In the case of a mesh heater, the constant value A may be in the range of 1.5 to 3. In the case of a mesh heater, the constant value A may be approximately 2.5.

[0048] For ceramic heaters, the constant value A may be in the range of 0.5 to 2.5. For ceramic heaters, the constant value A may be approximately 1.25.

[0049] For wick-coil heaters, the constant value A may be in the range of 0.5 to 3. For wick-coil heaters, the constant value A may be about 1.0 or about 1.5.

[0050] The controller of the aerosol generation system may be configured to transition the aerosol generation system to a locked state if a malfunction is determined. The malfunction may be detection of the heating element entering or about to enter a dry wick state. In the dry wick state, aerosol formation may result in undesirable aerosol constituents. Excessive heating in the dry wick state may also lead to destruction of the heating element. In the locked state, operation of the heating element may be prevented.

[0051] The controller of the aerosol generating system may be configured to transition the aerosol generating system to a locked state in a one-stage triggering process. In this case, the aerosol generating system is transitioned to the locked state when the condition defined in equation (2) is met. Hence, the aerosol generating system is transitioned to the locked state when a statistically significant increase in the electrical resistance ratio ΔR / Δt occurs and the deviation of the electrical resistance ratio ΔR / Δt from the running average sn exceeds a threshold Aσ. In the locked state, operation of the heating element is prevented until the user replaces or refills the cartridge.

[0052] The controller of the aerosol generating system may be configured to transition the aerosol generating system to a locked state in a two-stage triggering process. In this case, the aerosol generating system is transitioned to a temporary locked state when a first trigger condition defined in equation (2) (also referred to herein as a "dry state") is met. When a dry state is detected, operation of the aerosol generating system may be locked only temporarily to allow the heating element to cool down. After this temporary lockout, the aerosol generating system is configured to resume operation. If a statistically significant increase is again detected within the next heating pulse and equation (2) is again satisfied, the aerosol generating system is transitioned to a permanent locked state. However, if a statistically significant increase is not detected within the next heating pulse and equation (2) is not satisfied, the aerosol generating system is considered to have returned to a wet state. In the wet state, normal operation of the aerosol generating system is possible.

[0053] The two-stage triggering process may be more reliable because the probability of a false positive detection of a dry condition is low. A single false positive detection does not lead to locking of the aerosol generation system. A permanent locking of the system occurs only when a detection of a dry condition is confirmed on a subsequent heating cycle.

[0054] As mentioned above, the sensitivity of the method can be adjusted by the selection of the constant value A in equation (2). In a two-stage trigger process, this parameter may be different for the first and second trigger steps. In particular, in a two-stage trigger process, the constant value may be increased in the second trigger step. By increasing the constant value A in the second trigger step, the threshold for detecting a dry state is increased, reducing the possibility of a second false positive result.

[0055] Additionally or alternatively, in a two-stage triggering process, the constant value A in the first triggering step may also be intentionally decreased, resulting in increased sensitivity in the first triggering step. This higher sensitivity may be advantageous, since it increases the probability of detecting a dry wick in time. However, by increasing the sensitivity, a higher number of false positives may be obtained in the first triggering step. In such a case, the higher constant value A may only be useful to effectively identify these false positives and enter into a permanent lockout when the dry wick condition of the second step is also met.

[0056] The duration of the temporary lockout in the two-stage process may be adjusted as deemed appropriate. Even with a fairly short duration of only a few seconds, significant cooling of the heating element may be achieved. The duration of the temporary lockout may be selected as deemed appropriate. The duration of the temporary lockout may be selected depending on the internal design of the device or depending on the user's preference. The duration of the temporary lockout may range from 0.01 to 10 seconds. The duration of the temporary lockout may range from 0.1 to 5 seconds. The duration of the temporary lockout may range from 1 to 3 seconds.

[0057] The electrical resistance ratio ΔR / Δt may be determined from the maximum resistance values ​​determined during the first two heating pulses of a heating cycle, where ΔR may be the difference in maximum resistance between the first and second heating pulses of a heating cycle, and the value of Δt is the pulse width between the two first heating pulses of the heating cycle.

[0058] It has been found that in some heating elements, the dry puff state can already be identified at the beginning of the puff by the electrical resistance ratio ΔR / Δt. Determining the dry puff state at the beginning of the puff is particularly reliable when heating elements in the form of mesh heaters are used. Detecting the dry puff at the beginning of the heating cycle may make it possible to identify the dry puff before the dry puff is actually performed. Therefore, the system may be shut down before the dry puff state occurs. This may help to prevent inhalation of undesired aerosol constituents and may help to prevent potential damage to the heating element.

[0059] The electrical resistance ratio ΔR / Δt may be determined from the difference between the maximum resistance values ​​of two successive heating cycles. In this case, ΔR may also be referred to as ΔRmax. The value of Δt is the length of the heating cycle. This method has been found to be reliable when used with ceramic heating elements. During a typical heating cycle, the maximum temperature and maximum resistance occurs at the end of the heating cycle. This detection is therefore performed at the end of the puff and at the end of the corresponding heating cycle. The system may be shut down immediately after a dry puff condition occurs. This may also help to prevent inhalation of undesirable aerosol constituents and may help to prevent potential damage to the heating element.

[0060] The electrical resistance ratio ΔR / Δt may be determined from the difference in the increase in resistance during a heating cycle determined for two successive heating cycles. The increase in resistance during a heating cycle is the difference between the minimum and maximum resistance values ​​determined for a given heating cycle. Typically, this increase is the difference between the resistance values ​​determined at the first and the last heating pulse. Hence, for each heating cycle, an increase in the range of resistance values ​​is determined. A significant increase in the range of resistance values ​​indicates the occurrence of a dry wick condition. In this case, ΔR may also be referred to as ΔRRANGE. The value of Δt is the length of the heating cycle. This method has been found to be reliable when used with wick-coil type heating elements. Again, during a typical heating cycle, the highest temperature and maximum resistance occur at the end of the heating cycle, so that the resistance range is determined at the end of each heating cycle. Thus, this detection is performed at the end of the puff and at the end of the corresponding heating cycle. The system may be shut down immediately after the dry puff condition occurs. This may also help to prevent inhalation of unwanted aerosol constituents and may help to prevent potential damage to the heating element.

[0061] The appropriate moment to collect resistance data to determine whether a dry wick condition has occurred or is about to occur may depend on the relative dimensions of the heating element and the wicking element.

[0062] In mesh heating elements, the wicking elements may be somewhat small compared to the size of the heating element. Therefore, a strong increase may be observed at the beginning of the heating cycle. Therefore, evaluation of the resistance reading at the beginning of the heating cycle is characteristic for the heating process of interest. Such evaluation allows very early detection of dry puffs.

[0063] In ceramic heating elements, the wicking element may be large compared to the size of the heating element. Therefore, a somewhat slower response is observed at the beginning of the heating cycle. Therefore, evaluation of the resistance reading at the end of the heating cycle is more reliable to characterize the heating process. Therefore, in this case, it may be advantageous to use ΔRmax to identify the dry wick condition.

[0064] In a wick-coil type heating element, the wicking element may have approximately the same size as the heating element. In this case, it is preferable to evaluate the resistance readings at the beginning and end of the heating cycle. Therefore, the change in range of heater temperature throughout the heating cycle is a suitable parameter for the electrical resistance ratio. Therefore, in this case, it may be advantageous to use ΔRRANGE to identify the dry wick condition.

[0065] When the detected resistance of the heater is plotted on a 2D plot versus time, the normal resistance curve may generally have a steep slope, i.e., it rises more quickly at the beginning as the temperature increases until the liquid boiling point, but as the boiling point is approached, more energy is required to heat the liquid and both the temperature and resistance ratio decrease. The shape of such a normal resistance curve may appear as a curved "Γ" defined by two legs that define an angle θ between them. The angle θ between the two legs and the distance between the first and last resistance readings are very consistent in the wet state of the wick. As the wick dries out, the electrical resistance ratio ΔR / Δt increases, resulting in a higher resistance. The angle θ and the distance between the first and last resistance readings increase in the dry wick region.

[0066] The electrical resistance ratio ΔR / Δt may be determined from the angle θ defined by two legs of a normal electrical resistance curve. The first leg may be approximated by a vertical line passing through a first point on the electrical resistance curve. The second leg may be defined as a linear average of the electrical resistance readings that define the second leg.

[0067] The value of the angle θ may be taken as a measure of the electrical resistance ratio ΔR / Δt and may be used in equation (2) to determine if a dry wick condition has occurred. This method has been found to be reliable when used with mesh heating elements. Again, during a typical heating cycle, the highest temperature and resistance occurs at the end of the heating cycle, so the resistance range is determined at the end of each heating cycle. This detection is therefore performed at the end of the puff and at the end of the corresponding heating cycle. The system may be shut down immediately after a dry puff condition has occurred. This may also help prevent inhalation of undesirable aerosol constituents and may help prevent potential damage to the heating element.

[0068] The angle θ may be calculated from the slope of the two legs of the electrical resistance curve. For this purpose, the two legs may be approximated by straight lines. The angle θ is then the angle defined between these straight lines. The slope may be determined by any suitable method known to those skilled in the art. The slope may be determined by considering the first and the last data points of a given heating cycle. The slope may be determined taking into account the curvature k(t) of the electrical resistance curve. Exemplary methods for determining the angle θ are further described in more detail below. Which of these methods is the most appropriate may depend on the required accuracy and how noisy the electrical resistance data is.

[0069] The aerosol generating system may comprise an electrical circuit. The electrical circuit may comprise a microprocessor, which may be a programmable microprocessor. The microprocessor may be part of a controller. The electrical circuit may comprise further electronic components. The electrical circuit may be configured to regulate the power supply to the heating element.

[0070] As used herein, "electrically actuated aerosol generating system" refers to a system that generates an aerosol from one or more aerosol-forming substrates. The aerosol generating system may comprise an aerosol generating device and an aerosol-generating article or cartridge. The aerosol-generating article may include an aerosol-forming substrate. The aerosol-forming substrate may be contained within a cartridge.

[0071] The term "aerosol-forming substrate" as used herein means a substrate capable of releasing volatile compounds capable of forming an aerosol. Such volatile compounds may be released by heating the aerosol-forming substrate.

[0072] The advantage of providing a cartridge is that the aerosol-forming substrate is protected from the surrounding environment. In some embodiments, ambient light cannot enter the cartridge as well, so that light-induced degradation of the aerosol-forming substrate can be avoided. Furthermore, a high level of hygiene can be maintained.

[0073] The aerosol-forming substrate may be contained within a refillable liquid reservoir within the aerosol generating device. The aerosol-forming substrate may be contained within a refillable cartridge within the aerosol generating system. The aerosol-forming substrate is preferably contained within a disposable cartridge within the aerosol generating system. The cartridge may be replaced after a single session of use or may be replaced after multiple sessions of use. This may allow a user to replace a depleted cartridge in a safe and efficient manner.

[0074] The aerosol-forming substrate may be in a liquid phase at room temperature. The terms "liquid" and "solid" as used herein refer to the state of the aerosol-forming substrate at room temperature. The aerosol-forming substrate may be a flowable liquid at room temperature. For liquid aerosol-forming substrates, certain physical properties of the substrate, such as vapor pressure or viscosity, are selected to be suitable for use in the aerosol generating system.

[0075] The aerosol-forming substrate may comprise a plant-derived material. The aerosol-forming substrate may comprise tobacco. The aerosol-forming substrate may comprise a tobacco-containing material containing volatile tobacco flavour compounds that are released from the aerosol-forming substrate upon heating. Alternatively, the aerosol-forming substrate may comprise a non-tobacco-containing material. The aerosol-forming substrate may comprise a homogenised plant-derived material. The aerosol-forming substrate may comprise a homogenised tobacco material. The aerosol-forming substrate may comprise at least one aerosol former. The aerosol former may be any suitable known compound or mixture of compounds that facilitates the formation of a dense and stable aerosol in use and is substantially resistant to thermal decomposition at the operating temperature of the system. Suitable aerosol formers are well known in the art and include, but are not limited to, polyhydric alcohols (such as triethylene glycol, 1,3-butanediol, glycerin, etc.), esters of polyhydric alcohols (such as glycerol monoacetate, diacetate, or triacetate), and aliphatic esters of mono-, di-, or polycarboxylic acids (such as dimethyl dodecanedioate, dimethyl tetradecanedioate, etc.). Preferred aerosol formers are polyhydric alcohols or mixtures thereof, such as triethylene glycol, 1,3-butanediol, and glycerin (most preferred). The aerosol-forming substrate may contain other additives and ingredients, such as flavorings.

[0076] In the case of liquid aerosol-forming substrates, certain physical properties of the substrate, such as vapor pressure or viscosity, are selected to make it suitable for use in the aerosol generating system. The liquid preferably comprises a tobacco-containing material, which contains volatile tobacco flavor compounds that are released from the liquid upon heating. Alternatively, or in addition, the liquid may comprise non-tobacco materials. The liquid may comprise water, ethanol or other solvents, plant extracts, nicotine solutions, and natural or artificial flavors. The liquid preferably further comprises an aerosol former. Examples of suitable aerosol formers are glycerin and propylene glycol.

[0077] The electric aerosol generating system may include additional components, such as a charging unit for recharging an on-board power supply in the electrically operated aerosol generating device.

[0078] The aerosol generating system may include a housing. The housing may comprise any suitable material or combination of materials. Examples of suitable materials include metals, alloys, plastics, or composites containing one or more of these materials, or thermoplastics suitable for food or pharmaceutical applications, such as polypropylene, polyetheretherketone (PEEK), polyethylene. The material is preferably light and not brittle.

[0079] The power source may be any suitable power source, for example a direct current voltage source such as a battery. The power source may be a lithium ion battery, a nickel metal hydride battery, a nickel cadmium battery, or a lithium-based battery (e.g., a lithium cobalt battery, a lithium iron phosphate battery, a lithium titanate battery, or a lithium polymer battery).

[0080] The power source may include a rechargeable lithium ion battery. The power supply may include another form of charge storage device, such as a capacitor. The power supply may require recharging. The power supply may have a capacity that allows for the storage of sufficient energy for one or more uses of the aerosol generating device. For example, the power supply may have a capacity sufficient to allow continuous generation of aerosol for approximately six minutes, corresponding to the typical time it takes to smoke one conventional cigarette, or multiples of six minutes. In another embodiment, the power supply may have a capacity sufficient to allow a predetermined number of puffs, or discontinuous activation.

[0081] The electrical circuit may be configured to initiate the supply of power from the power supply to the heating element at the start of a heating cycle.The electrical circuit may be configured to terminate the supply of power from the power supply to the heating element at the end of a heating cycle.

[0082] The electrical circuit may be configured to provide a continuous supply of power from the power source to the heating element.

[0083] The electrical circuit may be configured to provide an intermittent supply of power from the power supply to the heating element.The electrical circuit may be configured to provide a pulsed supply of power from the power supply to the heating element.

[0084] Pulsing the power to the heating element may facilitate control of the total output from the heating element over a period of time. Advantageously, controlling the total output from the heating element over a period of time may facilitate control of the temperature.

[0085] The electrical circuit may be configured to vary the power supply from the power source to the heating element. The electrical circuit may be configured to vary the duty cycle of the pulsed supply of power. The electrical circuit may be configured to vary at least one of the pulse width and the duration of the duty cycle.

[0086] The present invention also relates to an electrically operated aerosol generating system comprising a heating element for heating an aerosol-forming substrate in the vicinity of the heating element, a power source for supplying power to the heating element, and an electrical circuit configured to regulate the supply of power to the heating element during a number of separate heating cycles. The electrical circuit is configured to determine an electrical resistance ratio ΔR / Δt of the heating element at a predetermined time interval and to calculate a moving average value of the electrical resistance ratio ΔR / Δt of the heating element during n preceding heating cycles, where n is an integer greater than 1, and to compare the electrical resistance ratio ΔR / Δt of the heating element to the calculated moving average value. The electrical circuit is further configured to determine a fault when the electrical resistance ratio ΔR / Δt is greater than the moving average value by more than a threshold value, and to control the power supplied to the heating element based on whether a fault is determined in the heating element.

[0087] The aerosol generating system may be portable. The aerosol generating system may have a size comparable to a conventional cigar or cigarette. The smoking system may have a total length of about 30 mm to about 150 mm. The smoking system may have an outer diameter of about 5 mm to about 30 mm.

[0088] The aerosol generating system may include a user input device. The user input device may include at least one of a push button, a scroll wheel, a touch button, a touch screen, and a microphone. The user input device may allow a user to control one or more aspects of the operation of the aerosol generating system. The user input device may allow a user to activate the supply of power to the heating element, or to deactivate the supply of power to the heating element, or both.

[0089] Features described with respect to one embodiment may be equally applied to other embodiments of the invention.

[0090] The invention will now be further described, by way of example only, with reference to the accompanying drawings in which: [Brief description of the drawings]

[0091] [Figure 1] FIG. 1 shows a prior art aerosol generating system that can be used in the present invention. [Diagram 2] FIG. 2 shows details of the cartridge of the aerosol generation system of FIG. [Diagram 3] FIG. 3 shows the mesh heating element in detail. [Figure 4] FIG. 4 is a plot showing the change in electrical resistance of various heating elements during a heating cycle. [Diagram 5] FIG. 5 is a plot showing the change in electrical resistance over the life of a mesh heating element. [Figure 6] FIG. 6 is a plot showing the change in electrical resistance upon transition to a dry state. [Figure 7]FIG. 7 is a plot showing the change in electrical resistance ratio of a mesh heater. [Figure 8] FIG. 8 is a plot showing the change in electrical resistance ratio of a ceramic heater. [Figure 9] FIG. 9 is a plot showing the change in electrical resistance ratio of a wick-coil heater. [Figure 10] FIG. 10 is a plot showing the change in mesh heater angle θ. [Figure 11] FIG. 11 illustrates a method for determining the angle θ. [Figure 12] FIG. 12 illustrates how to determine the angle θ by using the curvature k(x) of the electrical resistance curve. [Figure 13] FIG. 13 illustrates a modification of the method of FIG. [Figure 14] FIG. 14 is a schematic diagram showing the steps of the two-trigger method.

[0092] 1a and 1B are schematic diagrams of a known electrically heated aerosol generating system that may be used in accordance with the method of the present invention. The aerosol generating system comprises an aerosol generating device 10 and a cartridge 20.

[0093] The cartridge 20 contains an aerosol-forming substrate in a cartridge housing 24 and is configured to be received in a cavity 18 in the device. The cartridge 20 is a disposable cartridge. A user may replace the cartridge 20 when the aerosol-forming substrate in the cartridge is depleted. Figure 1a shows the cartridge 20 immediately prior to insertion into the device 10, with arrow 1 in Figure 1a indicating the direction of insertion of the cartridge 10.

[0094] The aerosol generating device 10 is portable and has a size comparable to a conventional cigar or cigarette. The device 10 comprises a body 11 and a mouthpiece portion 12. The body 11 contains a battery 14 (such as a lithium iron phosphate battery), an electrical circuit 16, and a cavity 18. The cavity 18 has a circular cross-section and is sized to receive the housing 24 of the cartridge 20.

[0095] The electrical circuitry 16 comprises a programmable microprocessor. The mouthpiece portion 12 is connected to the main body 11 by a hinged connection 21 and is movable between an open position as shown in FIG. 1a and a closed position as shown in FIG. 1b. The mouthpiece portion 12 is in an open position to allow insertion and removal of a cartridge 20 and is in a closed position when the system is used to generate an aerosol. The mouthpiece portion comprises a plurality of air inlets 13 and air outlets 15. In use, a user inhales or puffs at the outlets to draw air from the air inlets 13 through the mouthpiece portion to the outlets 15 and then into the user's mouth or lungs. An internal baffle 17 is provided to force air flow through the mouthpiece portion 12 and past the cartridge.

[0096] Figure 1b shows the system of Figure 1a with the mouthpiece portion 12 in a closed position. The mouthpiece portion 12 is held in the closed position by a clasp mechanism. The mouthpiece portion 12 in the closed position keeps the cartridge in electrical contact with the electrical connector 19 so that a good electrical connection is maintained during use regardless of the orientation of the system.

[0097] FIG. 2 is an exploded view of cartridge 20. Cartridge housing 24 has a size and shape selected to be received within cavity 18. The housing contains capillary material 27, 28 that is immersed in a liquid aerosol-forming substrate. In this example, the aerosol-forming substrate includes 39 weight percent glycerin, 39 weight percent propylene glycol, 20 weight percent water and flavorings, and 2 weight percent nicotine. Capillary material is a material that actively transports liquid from one end to the other based on the relative difference in liquid concentration. The capillary material may be made of any suitable material. In this example, the capillary material is formed from polyester.

[0098] Cartridge housing 24 has an open end in which a heating element 30 is secured. Heating element 30 comprises a base 34 having an opening 35 formed therein, a pair of electrical contacts 32 secured to the base and separated from one another by gaps 33, and a plurality of conductive heater filaments 36 spanning the opening and secured to the electrical contacts on opposite sides of opening 35.

[0099] The heating element 30 is covered by a peelable seal 26. The peelable seal 26 comprises a liquid impermeable plastic sheet that is adhered to the heating element 30 but is easily peelable. Tabs are provided on the sides of the peelable seal 26 to allow a user to grasp the peelable seal 26 when peeling. It will be apparent to one of ordinary skill in the art that although adhesion is described as a method of securing the impermeable plastic sheet to the heating element, other methods familiar to those skilled in the art may also be used, including heat sealing or ultrasonic welding, so long as the cover can be easily removed by the consumer.

[0100] The cartridge of Figure 2 has two separate capillary materials 27, 28. A disk of the first capillary material 27 is provided for contacting the heating elements 36, 32 in use. A larger body of the second capillary material 28 is provided on the opposite side of the first capillary material 27 to the heating elements. Both the first and second capillary materials hold a liquid aerosol-forming substrate. The first capillary material 27, which is in contact with the heating element, has a higher pyrolysis temperature (at least 160°C or higher, such as about 250°C) than the second capillary material 28.

[0101] The capillary material 27, 28 is advantageously oriented within the housing 24 to deliver the liquid to the heating element 30. When the cartridge is assembled, the heater filaments 36 may contact the capillary material 27 so that the aerosol-forming substrate can be delivered directly to the mesh heater. Figure 3 is a detailed view of the filaments 36 of the heating element 30, showing the meniscus 40 of the liquid aerosol-forming substrate between the heater filaments 36. It can be seen that the aerosol-forming substrate contacts most of the surface of each filament 36 such that most of the heat generated by the heating element 30 goes directly into the aerosol-forming substrate.

[0102] Thus, in normal operation, the liquid aerosol-forming substrate contacts a large portion of the surface of the heater filament 36. However, when most of the liquid substrate in the cartridge is used, less liquid aerosol-forming substrate will be delivered to the heater filament 36. With less liquid to vaporize, the enthalpy of vaporization requires less energy, and more energy provided to the heater filament 36 is directed toward increasing the temperature of the heater filament. Similarly, the energy required to maintain the target temperature also decreases as the heater filament 36 dries. The heater filament 36 may dry out because the aerosol-forming substrate in the cartridge has been depleted. Alternatively, but less likely, the heater filament 36 may dry out because the user is taking very long or very frequent puffs and is unable to deliver liquid to the heater filament 36 as fast as the liquid is vaporized.

[0103] In use, the heating element 30 operates by resistive heating. An electrical current is passed through the filament 36 under the control of the control electronics 16, heating the filament to within the desired temperature range. The mesh or array of filaments has a significantly higher electrical resistance than the electrical contacts 32 and electrical connectors such that the high temperature is localized to the filament. This minimizes heat loss to other components of the aerosol generating device 10. In this embodiment, the system is configured to generate heat by providing an electrical current to the heating element 30 in response to a user's puff.

[0104] The system includes a puff sensor configured to detect when a user is drawing air through the mouthpiece portion. The puff sensor (not shown) is connected to the control electronics 16, which is configured to supply electrical current to the heating element 30 only when it is determined that the user is puffing on the device. Any suitable airflow sensor may be used as the puff sensor (such as a microphone or pressure sensor).

[0105] To detect an increase in the heater filament temperature, the electrical circuit 16 is configured to measure the heater filament's electrical resistance. The heater filaments in this embodiment are formed from stainless steel and therefore have a positive temperature coefficient of resistance. In addition, in such puff-activated systems, heat is generated in short bursts using high current pulses, making stainless steel filaments ideal because of their relatively high specific heat capacity. As the temperature of the heater filaments 36 increases, so does their electrical resistance.

[0106] The plots in Figures 4a-4c exemplarily illustrate the change in resistance of various heating elements during two successive heating cycles, each of which corresponds to a user's puff. The plot in Figure 4a relates to two successive heating cycles of a mesh heating element. The plot in Figure 4b relates to a ceramic heating element. The plot in Figure 4c relates to a core-coil type heating element.

[0107] In each of Figures 4a-c, the left plot shows the increase in resistance when the heating element is in a wet state where sufficient liquid substrate is available for vaporization, and in each of Figures 4a-c, the right plot shows the increase in resistance when the heating element is in a dry state where sufficient liquid substrate is not available for vaporization.

[0108] Each heating cycle consists of 14 electrical pulses. For each electrical pulse, a dot indicates the maximum resistance measured during the pulse. The x-axis represents the time scale and the y-axis represents the measured electrical resistance at the heating element 30.

[0109] The heating element 30 has an initial resistance R ini The initial resistance R ini is an intrinsic property of the heating element 30. It represents the baseline resistance of the heating element 30 at room temperature.

[0110] As power is applied to the heating element 30 during a user's puff, the temperature of the heater filament 36 increases from the ambient temperature. This causes the electrical resistance R of the heater filament 36 to increase.

[0111] The resistance of the heater filament 36 is related to the heater temperature in the temperature range of interest by equation (1). Thus, by actively measuring the electrical resistance, an electrical circuit can determine the heater temperature at the heating element 30.

[0112] As can be seen in the plot of FIG. 4a, which shows the increase in resistance in the mesh heating element, the resistance increases especially at the beginning of the heating cycle. Hence, the electrical resistance ratio ΔR / Δt between the first two heating pulses in each heating cycle P2-P1 The increase in is used as the monitored parameter in equation (2).

[0113] This electrical resistance ratio ΔR / Δt P2-P1 The moving average of the previous 10 measurements of s 10, and the standard deviation σ in the form of a moving average of the previous 30 measurements of this electrical resistance ratio are determined. These parameters are inserted into equation (2) leading to the following equation:

[0114]

number

[0115] where A is a constant parameter of 2.5. Electrical resistance ratio ΔR / Δt P2-P1 exceeds the product of the standard deviation σ and a certain parameter A, the mean s 10 When the temperature increases relative to 0.5° C., a dry core condition of the mesh heating element is detected.

[0116] The plot in FIG. 4b shows the increase in resistance in a ceramic heating element. In this case, the resistance also increases, but the increase is especially noticeable at the end of the heating cycle. The increase in the electrical resistance ratio over a complete heating cycle, ΔR / Δt, is used as the monitored parameter in equation (2): MAX It is determined from the maximum temperature measured throughout.

[0117] This electrical resistance ratio ΔR / Δt MAX The previous 10 measurements of s 10 and the standard deviation σ in the form of a moving average σ of the previous 30 measurements of this electrical resistance ratio are determined. These parameters are inserted into equation (2) leading to the following equation:

[0118]

number

[0119] where A is a constant parameter of 1.25. Electrical resistance ratio ΔR / Δt MAX exceeds the product of the standard deviation σ and a certain parameter A, the mean s 10 When the temperature rises to 100° C., a dry core condition of the ceramic heating element is detected.

[0120] The plot in Figure 4c shows the increase in resistance for a core-coil type heating element. In this case, the electrical resistance ratio ΔR / Δt RANGE The increase in is determined from the increase in the temperature range of the heating element during a complete heating cycle, where the temperature range is the difference between the maximum and minimum temperatures during the heating cycle. The parameter ΔR / Δt in Eq. (2) RANGE Using as the monitored parameter leads to the following equation:

[0121]

number

[0122] where A is a constant parameter of 1 or 1.5. Electrical resistance ratio ΔR / Δt RANGE exceeds the product of the standard deviation σ and a certain parameter A, the mean s 10 When the temperature increases, a dry wick condition is detected in a wick-coil type heating element.

[0123] FIG. 5 shows experimental data where the resistance R is plotted for the life cycle of a mesh heating element. In the initial phase 50 of the experiment, the heating element fills up, which causes spit (bursting of bubbles due to rapid liquid heating). Thus, the shape of the resistance curve fluctuates slightly at the beginning of the test until a stable and reproducible form is reached. This main phase of optimal operation is called the "wet state" 52. In the wet state 52, the heating element is in good condition and the final resistance of each puff remains constant. In the end phase 54 of the test, a momentary increase in resistance is detected. This increase corresponds to the heating element entering the dry state 56. In the final phase 58, also called the runaway phase, the heater resistance increases exponentially and the heating element begins to glow. The heater temperature will rise to a maximum temperature of over 1200 degrees Celsius before burning out completely.

[0124] Figure 6 shows experimental data similar to that of Figure 5, but again testing a mesh heating element. The experimental curve shown in Figure 6 is reproduced with much higher resolution. Three main stages can be seen: an initial stage 50 where the bubbles burst, a main stage where the heating element is in a wet state 52, and a sudden increase in resistance indicating the heating element has entered a dry state 56.

[0125] FIG. 7 again shows the experimental data for the mesh heating element. In this diagram, the electrical resistance ratio ΔR / Δt is also determined from equation (5). P2-P1 The result is shown by curve 60. At the initial stage 50, the electrical resistance ratio fluctuates somewhat, leading to a partial increase in value. The increase is small enough that the dry trigger is not met correctly. During the wet state 52, the electrical resistance ratio remains rather constant and increases only when the heating element enters the dry state 56. The red line 62 in FIG. 7 represents the logic output from the dry wick detection method of the present invention. This logic output is "0" at the initial stage 50 and during the wet state 52, and increases to "1" when the dry state is detected. In the present invention, the dry wick state 56 was detected with a correct puff. The enlarged view shows further details of the heating element's transition between the wet state 52 and the dry state 56. The method was triggered by a puff just before the red line 62 during the first two heating pulses of this heating cycle. Thus, in this heating cycle, the heating process was interrupted and the immediate puff would not have been completed.

[0126] Similar data is depicted for a ceramic heating element in FIG. 8. The resistance of the ceramic heating element is very consistent in the wet state 52. The resistance increases in the dry state 56 for 2-3 puffs before rapidly decreasing as the metal elements of the ceramic heating element begin to melt. For this element, the electrical resistance ratio ΔR / Δt MAX is used as shown in equation (4). This electrical resistance ratio is also shown in Figure 8 as curve 60. Using this electrical resistance ratio as the key parameter leads to the detection of dry state 56 as shown by red line 62 in Figure 8. The method was triggered by the puff just to the left of red line 62, which corresponds to the first puff in the dry state 56 of the heating element.

[0127] FIG. 9 shows experimental data for a wick-coil type heating element. In this case, the resistance increases enormously when the wick enters the dry state 56. Nevertheless, it may not be possible to reliably identify the dry state 56, since an increase in resistance also occurs in the wet state 52. Therefore, the electrical resistance ratio ΔR / Δt, which takes into account the total change in resistance during the heating cycle, RANGE is used as the determining parameter according to equation (5). As can be seen in FIG. 9, during the wet state 52, the electrical resistance ratio ΔR / Δt RANGE remains largely constant, as observed for the mesh and ceramic heating elements. Again, the method identifies the dry state 56 at the correct puff, indicated by the red line 62 in Figure 9. The method was triggered by the puff just to the left of the red line 62, which corresponds to the first puff at the dry state 56 of the heating element.

[0128] FIG. 10 again shows the experimental data for the mesh heating element. The curve marked with a blue frame shows the heating element in a wet state 52. The curve marked with a red frame shows the heating element in a dry state 56. In the enlarged view, the angle θ is determined as a measure of the electrical resistance ratio ΔR / Δt. The angle θ is defined by two legs 64, 66. The first leg 64 may be approximated by a vertical line passing through a first point of each of the electrical resistance curves. The second leg 66 may be defined as the linear average of the electrical resistance readings at a later stage of the corresponding heating cycle.

[0129] 10, the angle θ is constant throughout the wet state 52, but increases significantly upon entering the dry state 56. Therefore, the angle θ may also be used as the decision parameter ΔR / Δt and inserted into equation (2) leading to the following equation:

[0130]

number

[0131] where A is a constant parameter of 2.5 and s 10 and σ correspond to the moving average and the standard deviation determined for the angle θ. The angle θ exceeds the product of the standard deviation σ and a constant parameter A to obtain the mean value s 10 When the temperature increases relative to 0.5° C., a dry core condition of the mesh heating element is detected.

[0132] The angle θ may be calculated from the slopes a1 and a2 of the two legs 64, 66 of the electrical resistance curve according to the following formula:

[0133]

number

[0134] a1 is the slope of the first leg 64 and a2 is the slope of the second leg 66 of the electrical resistance curve. A first method for determining the slopes of the two legs of the electrical resistance curve is illustrated in Fig. 11. In a first step, the extreme slopes L1 and L2 of the electrical resistance curve are determined, as illustrated in the left diagram of Fig. 10. For this purpose, the first 10 data points of the first leg and the last 10 data points of the second leg are considered. Depending on the quality of the data, a higher or lower number of data points can be considered. In a next step, the arithmetic mean of these two slopes is determined, resulting in an average slope L = (L1 + L2) / 2.

[0135] In the third step, illustrated in the center diagram of Figure 11, a data point (tL,RL) is identified where the slope of the electrical resistance curve corresponds to the previously determined average slope L. This may be done by running a function ΔR / Δt through the data set, for example by an algorithm using a fixed number of data points for the spans ΔR and Δt.

[0136] The data points (tL, RL) are used to define two straight lines that approximate the two legs of the electrical resistance curve. The first straight line is the line that passes through the data points (t1, R1) and (tL, RL). The second straight line is the line that passes through the data points (tL, RL) and (tN, RN). This is shown in the right diagram of Figure 10.

[0137] The slopes a1 and a2 are then calculated using the following formula:

[0138]

number

[0139]

number

[0140] The values ​​of the tilts a1 and a2 may be inserted into equation (7) to obtain the angle θ.

[0141] A further method for determining the two slopes utilizes the curvature k(t) of the electrical resistance curve, which is illustrated in Figure 12, which shows the curvature of the electrical resistance curve.

[0142] The curvature k(t) can be calculated from the following formula:

[0143]

number

[0144] As can be seen from FIG. 12, the curvature k(t) exhibits an extreme point. This extreme point is the point where the curvature reaches its maximum value and where the corresponding graph is the most "bent". This point can be considered to define the transition point from the first leg of the electrical resistance curve to the second leg of the electrical resistance curve. This extreme point may be used again as data point (tL, RL) for the definition of two straight lines approximating the two legs of the electrical resistance curve, as discussed in connection with FIG. 11. The slopes a1 and a2 may then be calculated again using the above equations (8) and (9).

[0145] Similar to the method of FIG. 11, it may be preferable to use certain predefined spans ΔR and Δt for the determination of the derivative. This may be particularly useful when the data contains increased electrical noise. The data set may also be smoothed by a filter function before the derivative is determined.

[0146] The extreme points of the curvature can be found by available system functions such as "findmax()" or can be calculated by searching for the zero value of the first derivative of k(t), which can be determined numerically using the Δk / Δt method.

[0147] The transition values ​​(tL,RL) determined by these two methods are not necessarily the same data points, however the results show that in both cases consistent results for detecting the electrical resistance ratio were obtained.

[0148] Figure 13 shows a modification of the method of Figure 12. In this method, two distinct points (tL1, RL1) and (tL2, RL2) are determined and then used to define straight lines a1 and a2 that approximate the first leg 64 and second leg 66 of the electrical resistance curve.

[0149] The two points (tL1,RL1) and (tL2,RL2) are defined by selecting a width w of the curvature extreme point, which in this case is defined by a percentage p of the curvature change of about 10% from the curvature extreme point.

[0150] It is believed that in order to correctly detect the dry core condition, one must determine the point in time when the angle θ begins to increase significantly. This increase is believed to be driven primarily by the runaway of the second leg 66 and less dependent on the inclination a1 of the first leg. It is therefore believed to be fully justified to approximate the inclination a1 of the first leg as being infinite and represented by a vertical line, as previously described.

[0151] Furthermore, it may not be necessary to take into account all data points of the second leg when determining the angle θ. In particular, if the runaway is fast and may cause destruction within a single heating cycle, the required data points may be limited to those after but near the curvature extreme points. In this way, it may be possible to determine within a single heating cycle whether a dry wick condition has been entered and to immediately shut off the power. Hence, this method may again make it possible to detect a dry wick condition at a very early stage and does not require the system to wait until the end of a given heating cycle.

[0152] As can be seen from the above, it is necessary to define a transition point to separate the data set into data points that define the first leg 64 and data points that define the second leg 66 of the electrical resistance curve. Which method is most appropriate may depend on the accuracy required and how noisy the electrical resistance data is.

[0153] FIG. 14 shows a flow chart illustrating the individual steps of the method of the invention using a two-trigger system. At start-up (step 70), the aerosol generating device is flagged as "wet", indicating that the device is ready for operation. Aerosol generation is initiated and the electrical resistance ratio ΔR / Δt is determined (step 72). The system status is then checked (step 74). Since the device is now flagged as "wet", the method will determine whether the electrical resistance ratio satisfies the "dry trigger" (step 76). If the dry trigger is not met, the aerosol generating device continues to be flagged as "wet" (step 78). The determined electrical resistance ratio is used to update the standard deviation σ and a new moving average s10 (step 80). The user may then continue the user experience by taking further puffs (step 82).

[0154] If the electrical resistance ratio ΔR / Δt increases significantly, such that the "dry trigger" is satisfied, the aerosol generator is flagged as "dry" (step 84). The system enters a "cooling period" during which the system is temporarily locked (step 86). The cooling period lasts for 5-10 seconds. This temporary locking of the system is barely perceptible by the user, as this period corresponds to the average pause between two consecutive puffs.

[0155] Once the "cooling period" has passed, the system is allowed to resume operation and the user may take a further puff (step 70). For this puff, aerosol generation is started again and the electrical resistance ratio ΔR / Δt is determined (step 72). Since the device was flagged as "dry" at the end of the previous puff, the method will now determine whether the electrical resistance ratio satisfies the "lockout trigger" (step 88). If the lockout trigger is indeed met (meaning that detection of a dry wick condition has been confirmed), the aerosol generating device will be permanently set to a locked out state (step 90). In such a case, the system will stop operation and the user will be prompted to change or refill the cartridge.

[0156] If the lockout trigger is not met, meaning that the wick dryness has not been confirmed, the aerosol generating device is again flagged as "wet" (step 92). The determined electrical resistance ratio is used to update the standard deviation σ and a new running average s10 (step 80). The user may then continue the user experience by taking further puffs.

[0157] The two triggers, the dryness trigger and the lockout trigger, can be adjusted by selecting different values ​​for the constant parameter A. If the same value is used for both triggers, essentially the same conditions are applied twice to recheck the dryness of the heating element. To increase sensitivity, a lower parameter A may be selected for the dryness trigger. However, such an increase in sensitivity may result in an increased number of false positives. To compensate for these false positives, a higher value of parameter A may be used for the lockout trigger. This may prevent the device from going into permanent lockout prematurely, i.e. when the wick is not actually yet dry.

Claims

1. 1. A method for controlling power supply to a heating element in an electrically operated aerosol generating system, comprising: adjusting the power supply to the heating element during a plurality of individual heating cycles; determining an electrical resistance ratio ΔR / Δt of the heating element at predetermined time intervals during a heating cycle; the moving average value s of the electrical resistance ratio ΔR / Δt of the heating element during n preceding heating cycles; n where n is an integer greater than 1; comparing the electrical resistance ratio ΔR / Δt of the heating element with the calculated moving average value; determining a fault when the electrical resistance ratio ΔR / Δt is greater than the moving average value by more than a threshold value; and controlling power supplied to the heating element based on whether a fault in the heating element is determined; The method of claim 1, wherein the threshold for determining a failure is determined from a standard deviation σ of the electrical resistance ratio ΔR / Δt.

2. The method of claim 1 , wherein power is supplied to the heating element during each heating cycle in a pulsed mode.

3. The method of any of claims 1 to 2, wherein power is supplied to the heating element in a fixed power mode or a fixed duty cycle mode.

4. The moving average s of the electrical resistance ratio ΔR / Δt n The method according to any one of claims 1 to 2, wherein n for determining is 5 to 30, preferably 10.

5. 2. The method of claim 1, wherein the threshold value for determining a failure is determined from the standard deviation σ of the electrical resistance ratio ΔR / Δt taking into account the running average of the resistance ratio ΔR / Δt determined over the previous 50, 30, 10 heating cycles, preferably the previous 30 heating cycles.

6. The method according to any one of claims 1 to 2, wherein the threshold value for determining a fault is determined from the product of the standard deviation σ of the electrical resistance ratio ΔR / Δt and a predetermined constant value.

7. The method according to any one of claims 1 to 2, wherein the predetermined constant value depends on the type of heating element used in the aerosol generating system.

8. The method according to any one of claims 1 to 2, wherein the predetermined constant value is about 2.5 for a mesh heater, about 1.25 for a ceramic heater, and about 1.5 for a wick-coil heater.

9. The method of any of claims 1 to 2, wherein the aerosol generation system is transitioned to a locked state if a malfunction is determined.

10. The method of any one of claims 1 to 2, wherein after a predetermined time has elapsed in the locked state, the aerosol generation system is unlocked so that operation of the heating element can resume.

11. 3. The method according to claim 1, wherein the heating element is a mesh heater, and the electrical resistance ratio ΔR / Δt is determined from a maximum resistance value determined in the first two heating pulses of a heating cycle.

12. The heating element is a ceramic heater, and the electrical resistance ratio ΔR / Δt is determined by successive heating cycles. max The method according to any one of claims 1 to 2, wherein the difference is determined from the difference between

13. The heating element is a core-coil type heating element, and the electrical resistance ratio ΔR / Δt is determined by successive heating cycles. range The method according to any one of claims 1 to 2, wherein the difference is determined from the difference between

14. 1. An electrically operated aerosol generating system comprising: a heating element for heating an aerosol-forming substrate in the vicinity of the heating element; a power source for supplying power to the heating element; 1. An electric circuit comprising: adjusting the power supply to the heating element during a plurality of individual heating cycles; determining an electrical resistance ratio ΔR / Δt of the heating element at predetermined time intervals; the moving average value s of the electrical resistance ratio ΔR / Δt of the heating element during n preceding heating cycles; n where n is an integer greater than 1, such that: The electrical resistance ratio ΔR / Δt of the heating element is calculated by the moving average value s n As compared to The electrical resistance ratio ΔR / Δt is n When the value is greater than the threshold, a fault is determined. and an electrical circuit configured to control power supplied to the heating element based on whether a fault in the heating element is determined; An aerosol generating system, wherein the threshold for determining a malfunction is determined from the standard deviation σ of the electrical resistance ratio ΔR / Δt.

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