Aerosol-generating device with feedback control of transducer

Abstract

To provide an aerosol-generating device using a liquid aerosol-forming substrate.SOLUTION: An aerosol-generating device may comprise a piezoelectric transducer (10). The aerosol generating device may comprise drive circuitry (12) connected to the piezoelectric transducer and configured to apply an oscillating current to the transducer. The aerosol-generating device may comprise control circuitry (14) connected to the drive circuitry and configured to monitor the resonant behaviour of the piezoelectric transducer, the control circuitry configured to control operation of the drive circuitry based on the resonant behaviour of the piezoelectric transducer.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present disclosure relates to aerosol-generating devices that use a liquid aerosol-forming substrate, and in particular to aerosol-generating devices that use a vibration transducer to move or atomize the liquid aerosol-forming substrate. [Background technology]

[0002] One example of an aerosol generating device is an e-cigarette. Typically in an e-cigarette, a liquid aerosol-forming substrate is heated to generate vapor to generate the aerosol. However, alternative designs have been proposed that use a vibration transducer to generate droplets from the liquid aerosol generating device, which then form the aerosol.

[0003] The vibration transducer can be used as the basis for a miniature liquid pump, which can be used in an aerosol generating device such as an e-cigarette to deliver a liquid aerosol-forming substrate from a reservoir to an atomizing element such as a heater or vibration transducer. Summary of the Invention [Problem to be solved by the invention]

[0004] It would be desirable to optimize as much as possible the efficiency of any vibration transducer used in an aerosol generating device to generate the aerosol or to move liquid within the device. This is particularly important in handheld aerosol generating devices such as e-cigarettes, which are typically battery-powered and desirably as small as possible, yet need to generate a significant amount of aerosol on demand by the user.

[0005] It would also be desirable to be able to quickly and simply detect any changing operating conditions that affect the output and efficiency of the aerosol generating device. [Means for solving the problem]

[0006] According to one aspect of the present invention, there is provided an aerosol generating device. The aerosol generating device may include a transducer. The transducer may be a piezoelectric transducer. The aerosol generating device may include a drive circuit connected to the transducer and configured to apply an oscillating current to the transducer. The aerosol generating device may include a control circuit connected to the drive circuit and configured to monitor the resonance behavior of the transducer, the control circuit being configured to control operation of the drive circuit based on the resonance behavior of the transducer.

[0007] As used herein, "resonance behavior" means any measurable aspect of the response of a piezoelectric transducer to a vibration input signal. For example, the resonant behavior may be the resonant frequency(ies) or change in the resonant frequency(ies), the maximum or minimum amplitude of the response, the maximum or minimum input impedance, or the phase response or change in the phase response.

[0008] The resonant behavior of a transducer may be represented by one or more measurable parameters, such as input impedance or one or more frequencies of maximum amplitude response.

[0009] The piezoelectric transducer may be part of a transducer assembly. The transducer assembly may be configured to interact with a liquid aerosol-forming substrate in the device. The transducer assembly may be configured to generate an aerosol from the liquid aerosol-forming substrate. The transducer assembly may be configured to move the liquid aerosol-forming substrate.

[0010] In some embodiments, the transducer assembly includes a perforated membrane or mesh. The transducer may be configured to vibrate the perforated membrane or mesh at one or more frequencies. The vibration of the perforated membrane or mesh may force the liquid aerosol-forming substrate through the perforated membrane or mesh, which may result in the formation of an aerosol containing droplets of the liquid aerosol-forming substrate.

[0011] In some embodiments, the transducer assembly includes a membrane or surface configured to contact the liquid aerosol-forming substrate. The transducer may be configured to vibrate the membrane or surface at one or more frequencies. The vibration of the membrane or surface may force the liquid through an adjacent mesh or perforated membrane, which may result in the formation of an aerosol containing droplets of the liquid aerosol-forming substrate.

[0012] In some embodiments, the transducer assembly includes an atomizing surface configured to contact the liquid aerosol-forming substrate and electrodes on the transducer configured to generate surface acoustic waves (SAW) on the atomizing surface, which generate droplets of the liquid aerosol-forming substrate, which form the aerosol.

[0013] In some embodiments, the transducer assembly forms part of a liquid pump. The transducer may include a membrane or surface configured to contact the liquid aerosol-forming substrate. The transducer may be configured to vibrate the membrane or surface at one or more frequencies. The vibration of the membrane or surface may force liquid through an adjacent liquid valve.

[0014] In all of these embodiments, it is beneficial to be able to control the operating frequency of the transducer or the operating power of the transducer (or both the operating frequency and the operating power of the transducer) in response to changes in the transducer's resonant behavior. Controlling the operating frequency, in particular, may be beneficial for improving the efficiency of the system. Controlling the operating frequency may allow for maximizing aerosol generation.

[0015] The control circuitry may be configured to control operation of the drive circuitry when the device is first powered up, and may be configured to control operation of the drive circuitry periodically or intermittently during operation of the device.

[0016] There are several reasons why the resonant behavior of a piezoelectric transducer may change during operation of the device. One parameter that may affect the resonant behavior of a transducer is temperature. The resonant frequency of the transducer assembly may change with temperature due to expansion or contraction of the materials of the transducer assembly, which may result in dimensional changes and changes in residual stresses within the transducer assembly. Temperature changes in the transducer assembly may occur due to changes in the ambient temperature. Temperature changes in the transducer assembly may occur due to warming of the transducer assembly as a result of energy dissipation within the device during operation. Typically, the transducer assembly warms up during operation of the device. Warming of the transducer assembly may result in a drop in the resonant frequency of the transducer.

[0017] Other changes in ambient conditions can affect the resonant behavior of the transducer, for example, changes in atmospheric pressure or humidity can affect the resonant behavior of the transducer.

[0018] A change in the material in contact with the transducer assembly can change the resonance behavior of the transducer. In particular, a change in the load on the transducer can change the resonance behavior of the transducer. For example, a change in the volume of the liquid aerosol-forming substrate in contact with the transducer assembly can change the load on the transducer. A change in the composition of the liquid aerosol-forming substrate in contact with the transducer assembly can change the load on the transducer.

[0019] The resonant behavior of a transducer may change as a result of aging of one or more components of the transducer assembly.

[0020] It can thus be seen that changes in the resonant behavior of the transducer assembly can be rapid or can involve longer term drift, and it would be beneficial for the device to be able to accommodate both rapid changes and longer term drift.

[0021] The control circuit may be configured to control operation of the drive circuit so that the oscillating current has a frequency equal to the resonant frequency of the piezoelectric transducer. Operating at the resonant frequency may allow a maximum amount of power to be transferred to the transducer. Operating at the resonant frequency may result in a maximum oscillation amplitude and a maximum oscillation velocity. This may be beneficial for generating an aerosol with desirable properties.

[0022] The control circuit may be configured to control operation of the drive circuit so that the oscillating current has a frequency offset from the resonant frequency of the transducer. This may be advantageous in some situations. For example, when the transducer's impedance at its resonant frequency does not match the drive circuit's output impedance, a small frequency offset is useful to operate the system at the impedance match point where the highest power is delivered to the transducer. This frequency may be between the resonant frequency and the anti-resonant frequency. In this region, the impedance changes significantly with frequency, allowing for precise tuning.

[0023] The control circuit may be configured to monitor the resonant behavior of the transducer at multiple resonant frequencies of the transducer corresponding to different modes of vibration, and the transducer may be driven at multiple different frequencies to generate aerosol droplets with different properties.

[0024] The control circuit may be configured to monitor the resonant behavior of the piezoelectric transducer by measuring the power delivered to the transducer or the input impedance of the transducer, at which frequency the delivered power is maximized and the input impedance is minimized.

[0025] The control circuit may be configured to monitor the resonant behavior of the piezoelectric transducer by determining zero crossing points or inflection points of the output signal from the transducer, and the zero crossing points or inflection points may be used to determine the operating frequency.

[0026] The control circuit may include a phase-locked loop (PLL). The phase-locked loop may include a phase comparator and may determine a phase shift in the response from the transducer. The use of a phase-locked loop may be advantageous because it does not require a microprocessor and may be a low-cost, reliable solution.

[0027] In some embodiments, the drive control circuitry comprises: a) applying a current having a drive frequency to the transducer; and b) applying a current having a second frequency during regularly spaced time slots, the second frequency being either higher or lower than the driving frequency; and c) determining whether the power delivered to the transducer is increased at the second frequency compared to the first frequency; and d) if the delivered power is increasing at the second frequency, use the second frequency as the drive frequency, otherwise maintain the existing drive frequency; and e) Steps a) to d) are repeated.

[0028] The drive circuit may use a second frequency higher than the drive frequency in the alternate time slots, and may use a second frequency lower than the drive frequency in the alternate time slots.

[0029] This process results in a device that automatically tracks the resonant frequency of the transducer.

[0030] The second frequency may be higher or lower than the drive frequency by a predetermined amount.

[0031] Another option for detecting changes in resonant frequency is the use of dedicated MEMS sensors. For example, a low-inertia MEMS cantilever can be placed in contact with the vibrating element of the transducer assembly so that the cantilever provides a corresponding electrical signal in synchronization with the transducer assembly's vibration. Another option is the use of real-time impedance measurement by monitoring the voltage and current across the transducer. In this case, the series and parallel modes of the transducer can be addressed separately. The transducer's behavior can be described in terms of an electrical equivalent circuit consisting of a capacitance C1, an inductance L1, and a resistance R1 in series with the mechanical components, and another capacitance C0 and resistance R0 in parallel with the transducer's electrical components. Depending on the frequency, this circuit can operate with the series branch (C1, L1, R1) resonating with itself (series resonant mode) or with this LCR series resonating with the parallel C0 (parallel resonant mode). The series resonant frequency is close to the transducer's resonant frequency, and the parallel resonant frequency is close to the transducer's antiresonant frequency. Series mode resonance provides low impedance and results in higher current and lower voltage for the same power. Mechanically, this provides a large displacement amplitude. Parallel mode resonance provides high impedance and results in lower current and higher voltage for the same power. Mechanically, the losses are lower. In this case, tuning series inductance can be added and the electroacoustic energy transfer efficiency can be higher at anti-resonance.

[0032] The device may include means for adjusting the resonant frequency of the transducer. For example, a membrane coupled to a piezoelectric transducer may be pre-stressed by application of a DC bias voltage, which will change its resonant behavior. As a component of device age, it may be beneficial to adjust the resonant response of the device to match a particular desired frequency or frequencies associated with the aerosol-forming substrate.

[0033] The control circuitry may comprise a microprocessor. The control circuitry may comprise a field programmable gate array (FPGA). The drive circuitry and the control circuitry may be integrated into a single circuit.

[0034] The control circuit may be configured to control the carrier frequency, duty cycle, power, modulation frequency or amplitude of the oscillating current from the drive circuit.

[0035] As described, the resonant behavior of the transducer may be affected by the amount of liquid in contact with portions of the transducer assembly. The control circuit may be configured to detect a reduction in the amount of liquid in contact with the transducer assembly based on a change in the resonant behavior of the transducer. This may be based on a sudden change in the resonant frequency greater than a threshold amount. The control circuit may be configured to disable operation of the drive circuit in response to detecting a significant reduction in the amount of liquid delivered to the transducer assembly. The control circuit may be configured to disable or modify operation of the drive circuit based on any malfunction of the device, as determined based on the resonant behavior of the transducer.

[0036] The piezoelectric transducer may comprise a single crystal material. The piezoelectric transducer may comprise quartz. The piezoelectric transducer may comprise a ceramic. The ceramic may comprise barium titanate (BaTiO3). The ceramic may comprise lead zirconate titanate (PZT). The ceramic may comprise a doping material such as Ni, Bi, La, Nd, or Nb ions. The piezoelectric transducer may be poled. The piezoelectric transducer may be unpoled. The piezoelectric transducer may include both poled and unpoled piezoelectric materials.

[0037] The drive circuit may be configured to apply an oscillating current having a frequency of about 20 kHz to about 1500 kHz, or about 50 kHz to about 1000 kHz, or about 100 kHz to about 500 kHz, which may provide a desired aerosol output rate and desired droplet size.

[0038] The aerosol generating device may be configured to generate an aerosol for inhalation by a user. The aerosol generating device may be an electrically operated smoking device.

[0039] The aerosol generating device may comprise a liquid reservoir containing a liquid aerosol-forming substrate. In use, the piezoelectric transducer may come into contact with liquid from the liquid reservoir.

[0040] The aerosol generating device may comprise a liquid storage portion containing a reservoir of liquid aerosol-forming substrate. The liquid storage portion may form part of a cartridge that is separable from the remainder of the device. The liquid storage portion of the aerosol generating system may comprise a substantially cylindrical housing, with the opening at one end of the cylinder. The housing of the liquid storage portion may have a substantially circular cross section. The housing may be a rigid housing. As used herein, the term "rigid housing" is used to mean a self-supporting housing. The rigid housing of the liquid storage portion may provide mechanical support for the heating means.

[0041] The liquid reservoir may further comprise a carrier material within the housing for holding the aerosol-forming substrate.

[0042] The liquid aerosol-forming substrate may be adsorbed or otherwise loaded onto a carrier or support. The carrier material may be made of any suitable absorbent plug or body, such as foam metal or plastic material, polypropylene, terylene, nylon fiber, or ceramic. The liquid aerosol-forming substrate may be retained in the carrier material before using the aerosol generating system. The liquid aerosol-forming substrate may be released into the carrier material during use. The liquid aerosol-forming substrate may be released into the carrier material immediately before use.

[0043] In one embodiment, the liquid aerosol-forming substrate is held within a capillary material. A capillary material is a material that actively transports liquid from one end of the material to another. The capillary material may be advantageously oriented within the housing to transport the liquid aerosol-forming substrate to the transducer assembly. The capillary material may have a fibrous structure. The capillary material may have a spongy structure. The capillary material may comprise a bundle of capillaries. The capillary material may comprise a plurality of fibers. The capillary material may comprise a plurality of threads. The capillary material may comprise fine tubes. The capillary material may comprise a combination of fibers, threads, and fine tubes. The fibers, threads, and fine tubes may generally be aligned to transport the liquid to the vibratable element. The capillary material may comprise a spongy material. The capillary material may comprise a foam-like material. The structure of the capillary material may form a plurality of small holes or tubes through which liquid can be transported by capillary action.

[0044] The capillary material may comprise any suitable material or combination of materials. Examples of suitable materials include sponge or foam materials, ceramic or graphite-based materials in the form of fibers or sintered powders, expanded metal or plastic materials, and fibrous materials, such as spun or extruded fibers (such as cellulose acetate, polyester, or bonded polyolefin, polyethylene, terylene, or polypropylene fibers, nylon fibers, or ceramics). The capillary material may have any suitable capillary action and porosity for use with different liquid physical properties. The liquid aerosol-forming substrate has physical properties, including but not limited to viscosity, surface tension, density, thermal conductivity, boiling point, and atomic pressure, that allow the liquid to be transported through the capillary material by capillary action. The capillary material may be configured to transport the aerosol-forming substrate to the transducer assembly.

[0045] The carrier material may abut the transducer assembly. The liquid aerosol-forming substrate may be transported from the liquid reservoir to the transducer assembly by capillary action.

[0046] Alternatively, or additionally, the apparatus may comprise a pump, and the liquid aerosol-forming substrate may be delivered from the reservoir to the transducer assembly by means of the pump.

[0047] The aerosol generating device may include a liquid aerosol-forming substrate within the liquid storage housing. The liquid aerosol-forming substrate is a substrate capable of emitting a volatile compound capable of forming an aerosol. The volatile compound may be emitted by moving the liquid aerosol-forming substrate through a passageway of a vibratable element.

[0048] The liquid aerosol-forming substrate may comprise nicotine. The nicotine-containing liquid aerosol-forming substrate may be a nicotine salt matrix. The liquid aerosol-forming substrate may comprise a plant-derived material. The liquid aerosol-forming substrate may comprise tobacco. The liquid aerosol-forming substrate may comprise a tobacco-containing material containing volatile tobacco flavour compounds that are released from the aerosol-forming substrate upon heating. The liquid aerosol-forming substrate may comprise a homogenised tobacco material. The liquid aerosol-forming substrate may comprise a non-tobacco-containing material. The liquid aerosol-forming substrate may comprise a homogenised plant-derived material.

[0049] The liquid aerosol-forming substrate may include at least one aerosol former. The aerosol former may be any suitable, well-known compound or mixture of compounds that facilitates the formation of a dense, stable aerosol during 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 (e.g., triethylene glycol, 1,3-butanediol, glycerin), esters of polyhydric alcohols (e.g., glycerol monoacetate, diacetate, or triacetate), and aliphatic esters of monocarboxylic, dicarboxylic, or polycarboxylic acids (e.g., dimethyl dodecanedioate, dimethyl tetradecanedioate). The aerosol former may be a polyhydric alcohol or a mixture thereof (e.g., triethylene glycol, 1,3-butanediol, glycerin). The liquid aerosol-forming substrate may also include other additives and ingredients (e.g., flavoring agents).

[0050] The aerosol-forming substrate may comprise nicotine and at least one aerosol former. The aerosol former may be glycerin. The aerosol former may be propylene glycol. The aerosol former may comprise both glycerin and propylene glycol. The aerosol-forming substrate may have a nicotine concentration of about 2% to about 10%.

[0051] The aerosol-forming substrate may have a kinematic viscosity (μ) at a temperature of 20° C. of from about 0.4 mPa.S (0.4 mPl, 0.4 cP) to about 1000 mPa.S (1000 mPl, 1000 cP), or from about 1 mPa.S to about 100 mPa.S, or from about 1.5 mPa.S to about 10 mPa.S.

[0052] The aerosol generating device may include a power source. The power source may be a battery. The battery may be a lithium-based battery, such as a lithium-cobalt battery, a lithium-iron-phosphate battery, a lithium-titanate battery, or a lithium polymer battery. The battery may be a nickel-metal hydride battery or a nickel-cadmium battery. The power source may be another form of charge storage device, such as a capacitor. The power source may require recharging and may be configured for numerous charge-discharge cycles. The power source may have a capacity that allows for storage of energy sufficient for one or more smoking experiences; for example, the power source 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 a multiple of six minutes. In another embodiment, the power source may have a capacity sufficient to allow for a predetermined number of puffs or discontinuous activation of the heating means and actuator.

[0053] The aerosol generating device may be portable. The aerosol generating device may have a size comparable to that of a conventional cigar or cigarette. The aerosol generating system may have a total length of about 30 mm to about 150 mm. The aerosol generating device may have an outer diameter of about 5 mm to about 30 mm.

[0054] The aerosol generating device may include a housing. The housing may be elongated. 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), or polyethylene. The material may be lightweight and not brittle.

[0055] The housing may include a cavity for receiving a power source. The housing may include a mouthpiece. The mouthpiece may include at least one air inlet and at least one air outlet. The mouthpiece may include two or more air inlets.

[0056] The action of the transducer assembly on the liquid aerosol-forming substrate may heat the aerosol-forming substrate. This may be desirable when it is desired to deliver a warm aerosol to the user. Alternatively, or additionally, the device may include a heater. The heater may heat the liquid aerosol-forming substrate before it reaches the transducer assembly, at the transducer assembly, or after the liquid aerosol-forming substrate has formed an aerosol.

[0057] In another aspect of the present invention, a method of operating an aerosol generating device is provided. The device may include a piezoelectric transducer. The device may include a drive circuit connected to the piezoelectric transducer. The device may include a control circuit configured to monitor a parameter of the piezoelectric transducer and connected to the drive circuit. The method may include applying an oscillating current to the transducer using the drive circuit. The method may further include monitoring a resonant behavior of the piezoelectric transducer using the control circuit. The method may further include controlling operation of the drive circuit based on the monitored resonant behavior of the piezoelectric transducer.

[0058] The piezoelectric transducer may be part of a transducer assembly. The transducer assembly may be within a liquid pump. The transducer assembly may include a membrane or surface configured to contact the liquid aerosol-forming substrate. The piezoelectric transducer may be configured to vibrate the membrane or surface. The vibration of the membrane or surface may force liquid through an adjacent liquid valve within the liquid pump.

[0059] The method may include deactivating the drive circuit based on the monitored resonant behavior of the piezoelectric transducer. The method may include controlling a carrier frequency, a duty cycle, a power, a modulation frequency, or an amplitude of an oscillating current from the drive circuit.

[0060] The step of monitoring the resonant behavior may include periodically applying an oscillating current at different frequencies and determining the resonant behavior of the transducer at the different frequencies. The method may include applying an oscillating current comprising a plurality of sinusoidal frequencies.

[0061] The present invention may provide the advantage of efficient operation throughout operation despite changes in load on the transducer and changes in ambient or device conditions. The present invention may also provide a means for detecting malfunctions and abnormal operating conditions, such as a reduced supply of liquid aerosol-forming substrate.

[0062] The present invention is defined in the claims. However, the following provides a non-exhaustive list of non-limiting examples. Any one or more of the features of these examples may be combined with any one or more features of any other example, embodiment, or aspect described herein.

[0063] Example 1: An aerosol generating device comprising a piezoelectric transducer, a drive circuit connected to the piezoelectric transducer and configured to apply an oscillating current to the transducer, and a control circuit connected to the drive circuit and configured to monitor the resonance behavior of the piezoelectric transducer, the control circuit configured to control the operation of the drive circuit based on the resonance behavior of the piezoelectric transducer. Example 2: An aerosol generating device as described in Example 1, wherein the control circuit is configured to control the operation of the drive circuit so that the oscillating current has a frequency equal to the resonant frequency of the piezoelectric transducer. Example 3: An aerosol generating device as described in Example 1, wherein the control circuit is configured to control the operation of the drive circuit so that the oscillating current has a frequency that is shifted from the resonant frequency of the piezoelectric transducer. Example 4: An aerosol generating device described in any one of Examples 1 to 3, wherein the control circuit is configured to monitor the resonant behavior of the piezoelectric transducer at multiple resonant frequencies of the piezoelectric transducer corresponding to different modes of vibration. Example 5: An aerosol generating device described in any one of Examples 1 to 4, wherein the control circuit is configured to monitor the resonant behavior of the piezoelectric transducer by measuring the current delivered to the piezoelectric transducer or the impedance of the piezoelectric transducer. Example 6: An aerosol generating device according to any one of Examples 1 to 5, wherein the drive circuit and control circuit comprise a phase-locked loop (PLL). Example 7: An aerosol-generating device according to any one of Examples 1 to 6, wherein the piezoelectric transducer is an aerosol-generating element configured to generate an aerosol from the liquid aerosol-forming substrate. Example 8: An aerosol generating device as described in Example 7, wherein the piezoelectric transducer comprises a perforated plate. Example 9: An aerosol generating device according to any one of Examples 1 to 6, wherein the piezoelectric transducer is part of a liquid pump. Example 10: An aerosol-generating device according to any one of Examples 1 to 9, comprising a liquid reservoir containing a liquid aerosol-forming substrate, and in use the piezoelectric transducer comes into contact with liquid from the liquid reservoir. Example 11: The aerosol generating device of Example 10, wherein the liquid comprises a mixture of different compounds. Example 12: An aerosol generating device as described in Example 10 or Example 11, wherein the control circuit is configured to detect a reduction in the amount of liquid in contact with the piezoelectric transducer based on a change in the resonance behavior of the piezoelectric transducer. Example 13: An aerosol-generating device according to any one of Examples 1 to 12, wherein the aerosol-generating device is an e-cigarette. Example 14: An aerosol generating device according to any one of Examples 1 to 13, wherein the oscillating current comprises a first frequency modulated with at least one other frequency. Example 15: A method of operating an aerosol generating device, the device comprising: a piezoelectric transducer; a drive circuit connected to the piezoelectric transducer; and a control circuit configured to monitor a parameter of the piezoelectric transducer and connected to the drive circuit, the method comprising: applying an oscillating current to the transducer using a drive circuit; monitoring the resonant behavior of the piezoelectric transducer using a control circuit; and controlling operation of the drive circuit based on the monitored resonant behavior of the piezoelectric transducer.

[0064] The embodiments will now be further described with reference to the following figures: [Brief explanation of the drawings]

[0065] [Figure 1] FIG. 1 illustrates a feedback control system according to the present invention. [Figure 2] FIG. 2 is a schematic diagram of an aerosol generating device according to the present invention. [Figure 3] FIG. 3 illustrates a transducer assembly for use in the system of FIG. [Figure 4] FIG. 4 is a schematic plot showing the change in transducer response over time. [Figure 5] FIG. 5 illustrates one embodiment of a drive control circuit that implements feedback control. [Figure 6] FIG. 6 is a schematic diagram of an aerosol generating device according to the present invention, comprising a piezoelectric pump. DETAILED DESCRIPTION OF THE INVENTION

[0066] FIG. 1 is a schematic diagram of a feedback control loop according to the present invention. The feedback loop includes a transducer 12, a driver circuit 14, and a control circuit 14. In this embodiment, the transducer is a piezoelectric transducer. The transducer is coupled to a membrane and vibrates the membrane to generate an aerosol from a liquid supply. The transducer 12 is driven at a particular drive frequency by a driver circuit 12. The driver circuit 12 supplies an oscillating current to the transducer, which causes the transducer to expand and contract. This, in turn, causes the membrane to vibrate.

[0067] A transducer has one or more resonant frequencies. The resonant frequencies depend on several factors, including the load on the transducer, which depends on the properties of the membrane and any load on the membrane. The resonant frequencies also depend, for example, on temperature.

[0068] To ensure that the transducer is driven at its resonant frequency by the drive circuit, the control circuit 14 completes a feedback loop. The control circuit receives a feedback parameter, such as a phase shift or vibration amplitude, from the transducer. The value of the feedback parameter varies depending on how close the drive frequency is to the transducer's resonant frequency. The drive circuit 12 adjusts the drive frequency of the oscillating current applied to the transducer 10, and the effect of this change in drive frequency on the feedback parameter is monitored by the control circuit. The control circuit then sends a control signal to the drive circuit, which adjusts the frequency of the applied oscillating current based on the control signal to achieve a particular effect. In many cases, it is desirable to drive the transducer as close to its resonant frequency as possible. However, in some situations, it may be desirable to drive the transducer at a specific offset from its resonant frequency or at a frequency between its resonant frequency and its anti-resonant frequency. The control circuit may include a filter, a microcontroller, or any analog or digital means to process the feedback parameter to generate a control signal.

[0069] Figure 2 is a schematic diagram of a first embodiment of an aerosol generating device according to the present invention incorporating the feedback control illustrated in Figure 1. Figure 2 is schematic in nature. In particular, the components shown are not necessarily to scale, either individually or relative to each other. The aerosol generating device comprises a reusable device portion 100 cooperating with a cartridge 200, which is preferably disposable. In Figure 2, the device is an electrically operated smoking system.

[0070] The device portion 100 comprises a main body having a housing 101. The housing 101 is substantially circular, cylindrical, and has a longitudinal length of about 100 mm and an outer diameter of about 20 mm, comparable to a conventional cigar. A power source in the form of a battery 102 and electrical control circuitry 104 is provided in the device. The electrical control circuitry 104 includes drive and control circuitry for the transducer, as described with reference to FIG. 1. The main body housing 101 also defines a cavity 112 for receiving a cartridge 200 therein.

[0071] Cartridge 200 (shown in schematic form in FIG. 2) comprises a rigid housing defining a liquid reservoir 201. Liquid reservoir 201 holds a liquid aerosol-forming substrate (not shown). The housing of cartridge 200 is fluid-tight but has an open end (not shown) that can be covered by a removable lid (not shown) when the cartridge is removed from device 100. The lid may be removed from cartridge 200 prior to insertion of the cartridge into the device. Cartridge 200 includes a keyed feature (not shown) to ensure that cartridge 200 cannot be inserted into the device upside down.

[0072] Device portion 100 also includes a mouthpiece portion 120. Mouthpiece portion 120 is connected to main body housing 101 by a hinged connection in this example, although any type of connection, such as a snap fit or threaded connection, may be used. Mouthpiece portion 120 includes a plurality of air inlets 122, air outlets 124, and aerosol-forming chambers 125, with atomizer 300 (shown schematically in FIG. 2) mounted therein. Air inlet 122 is defined between mouthpiece portion 120 and main body housing 101 of device 100 when the mouthpiece portion is in the closed position, as shown in FIG. 2. An airflow route 127 is formed from air inlet 122, through aerosol-forming chamber 125 and atomizer 300, to air outlet 124, as indicated by the arrows in FIG. 2.

[0073] As shown in Figure 3, atomizer 300 comprises a vibratable element 301 and a transducer 302 housed within atomizer housing 304. The atomizer housing 304 comprises a hollow cylindrical box having an inlet opening 305 and an outlet opening 306 disposed in coaxial alignment on opposite sides of the housing 304. The housing 304 is removably connected to the mouthpiece 120 of the device portion 100 by a threaded connection (not shown). Male threads (not shown) are provided on the outer surface of the atomizer housing 304, which are complementary to female threads (not shown) on the inner surface of the mouthpiece 120. The atomizer 300 is removable from the mouthpiece portion 120 of the device portion for disposal or cleaning.

[0074] The vibratable element 301 comprises a substantially circular aluminum disc having a thickness of about 2 mm and a diameter of about 15 mm.

[0075] A plurality of passages 303 extend from an inlet side 308 of the vibratable element to an opposite outlet side 309. The plurality of passages form an array having a substantially circular shape. The substantially circular array has a diameter of about 7 mm and is substantially centrally disposed within the element 301.

[0076] The passages (not shown) have a substantially circular cross-section and taper from the inlet side 308 to the outlet side 309 of the vibratable element 301. The passages have a diameter of about 8 μm on the inlet side and about 6 μm on the outlet side. The passages are typically formed by high-speed laser drilling. The plurality of passages consists of about 4000 passages evenly spaced across the array.

[0077] The transducer 302 comprises a piezoelectric transducer, which is a substantially circular annular disk of piezoelectric material, typically lead zirconate titanate (PZT). The piezoelectric transducer has a thickness of about 2 mm, an outer diameter of about 17 mm, and an inner diameter of about 8 mm.

[0078] 3, the transducer 302 is in direct contact with the vibratable element 301 at the outlet side 309 of the vibratable element. The inner diameter of the piezoelectric transducer 302 surrounds the array of passages 303 of the vibratable element 301, such that the open ends of the passages at the outlet side are not covered by the piezoelectric transducer 302. It is contemplated that in other embodiments (not shown), the piezoelectric transducer 302 may be in direct contact with the vibratable element 301 at the inlet side 308.

[0079] The vibratable element 301 and piezoelectric transducer 302 are supported within the atomizer housing 304 by a pair of elastomeric O-rings 311, which allow the vibratable element 301 and piezoelectric transducer 302 to vibrate within the housing 304. The vibratable element 301 and piezoelectric transducer 302 are held together by pressure from the opposing O-rings 311. However, in other embodiments (not shown), the vibratable element 301 and piezoelectric transducer 302 may be joined by any suitable means, such as an adhesive layer.

[0080] The vibratable element 301 and piezoelectric transducer 302 are disposed within the atomizer housing 304 such that the array of passages 303 is coaxially aligned with the inlet opening 305 and the outlet opening 306 of the housing 304 .

[0081] One or more spring pins 310 extend through openings 312 in the atomizer housing 304 to provide electrical connection of the piezoelectric transducer 302 to the control electronics 104 and battery 102 of the device 100. The one or more spring pins 310 are held in contact with the piezoelectric transducer 302 by pressure rather than mechanical connection so that good electrical contact is maintained during vibration of the piezoelectric transducer 302.

[0082] In use, when the atomizer 300 is removably connected to the mouthpiece portion 120 of the device portion 100 and the cartridge 200 is received within the device cavity 112, an elongated capillary body (not shown in FIG. 2) extends from the liquid storage portion 201 of the cartridge 200 to the atomizer 300, fluidly connecting the cartridge 200 to the atomizer 300. As shown in FIG. 3, the elongated capillary body 204 extends into the atomizer housing 304 and abuts the inlet sides 308 of the vibratable elements 301 in the array of passages 303. Heating means is provided within the liquid storage portion in the form of a coil heater 205 surrounding the capillary body 204. It should be noted that the coil heater is only shown schematically in FIG. 3. The coil heater 205 is connected to the electrical circuitry 104 and battery 102 of the device 100 via connections (not shown) that may run along the outside of the liquid storage portion 200, but this is not shown in Figures 2 or 3.

[0083] In use, a liquid aerosol-forming substrate (not shown) is carried by capillary action from the liquid storage portion 201, from the end of the capillary body 204 that extends into the liquid storage portion 201, past the heater coil 205, to the other end of the capillary body 204, which extends into the atomizer housing 304 and abuts the vibrable elements 301 in the array of passages 303 on the inlet side 308.

[0084] When a user draws on air outlet 124 of mouthpiece portion 120, ambient air is drawn through air inlet 122. In the embodiment of Figure 2, a puff detection device 106 in the form of a microphone is also provided as part of control electronics 104. A small airflow is drawn through sensor inlet 121 in main body housing 101, past microphone 106, and into mouthpiece portion 120. When a puff is detected by electrical circuitry 104, electrical circuitry 104 activates heater coil 205 and piezoelectric transducer 302. Battery 102 supplies electrical energy to coil heater 205, which heats capillary body 204 surrounded by the coil heater.

[0085] The battery 102, under the control of the drive control circuit, further supplies electrical energy to the piezoelectric transducer 302, which causes the piezoelectric transducer 302 to vibrate and deform in its thickness direction. The piezoelectric transducer 302 typically vibrates at approximately 150 kHz. The drive current supplied to the transducer has an initial frequency and waveform based on parameters stored in memory. During device manufacturing, the frequency response of the transducer assembly including the vibratable element 301 can be characterized, and the initial frequency and waveform are set. The piezoelectric transducer 302 transmits the vibrations to the vibratable element 301, which vibrates and deforms in its thickness direction. The LED 108 is also activated to indicate that the device is activated. As will be described, during operation, a feedback control loop is used to adjust the drive current supplied to the transducer in response to detected changes in resonant behavior.

[0086] The coil heater 205 heats the liquid aerosol-forming substrate that is conveyed along the capillary body and past the coil heater 205 to a predetermined temperature of about 45°C.

[0087] Vibrations within the vibratable element deform the plurality of passages 303, which draws heated liquid aerosol-forming substrate from the capillary body 204 through the plurality of passages 303 on the inlet side 308 of the vibratable element 301 and expels atomized droplets of the liquid aerosol-forming substrate through the passages on the outlet side 309 of the vibratable element 301, forming an aerosol. Simultaneously, the atomized, heated liquid is displaced by additional liquid moving along the capillary body 204 by capillary action (this is sometimes referred to as a pumping action). The aerosol droplets expelled from the vibratable element 301 mix with the airflow 127 from the inlet 122 within the aerosol-forming chamber 125, are carried in the airflow 127, and are transported toward the air outlet 124 of the mouthpiece 120 for inhalation by the user.

[0088] As mentioned above, the resonant response of a transducer may change during operation. Figure 4 is a schematic plot of a sensed parameter from a transducer showing the change in frequency over time. The time difference between successive crossings of the signal to zero is a measure of frequency and may be used to synchronize the drive signal with the operating frequency of the transducer (in this example, its resonant frequency). The signal may be, for example, a current measured by a sense resistor in series with the transducer. In that case, the amplitude may have units of amperes for current, or the amplitude may be normalized, for example, by its maximum value, in which case the units of amplitude are 1. The time may have units of milliseconds or microseconds, depending, for example, on the operating range of the characteristic frequency handled by the transducer.

[0089] One example of a possible implementation of such a feedback loop is shown in FIG. 5. In the embodiment of FIG. 3, a transducer 500 connected to a vibrable perforated plate is driven by a half-bridge 505 consisting of two power MOSFETs 510 and 515. An optional series inductor 520, such as a 10 microhenry inductor, may be used between the half-bridge and the transducer to adjust the impedance. A current-sense resistor 525, for example, a 1 ohm resistor, may be placed at the bottom of the transducer 500. The voltage measured across the current-sense resistor is proportional to the current through the transducer. This voltage signal may be filtered and amplified by a filter and gain stage 530. The filter and gain stage 530 may include, for example, a low-pass filter to block high-frequency harmonics and a FET amplifier, such as an AD823, to amplify the signal. A comparator 540 generates a feedback signal (in this example, a square wave signal) as an appropriate input waveform for a gate driver 550. A gate driver 550, which may be, for example, a type LT1162 IC, drives the half-bridge 505. Frequency changes are detected and sent back to the driver so that the transducer 500 is always driven at its operating frequency, e.g., its resonant frequency. The drive control circuit shown in Figure 5 can be incorporated into the control circuit 104 shown in Figure 2.

[0090] Figure 6 is a diagram of an aerosol-generating device according to another embodiment of the present invention. Figure 6 is schematic in nature. In particular, the components shown are not necessarily to scale, either individually or relative to each other. The device of Figure 6 generates an aerosol by heating a liquid aerosol-forming substrate using a heater. However, the device includes a pump that uses a piezoelectric transducer to transport the liquid aerosol-forming substrate to the heater.

[0091] The device is a handheld, electrically operated smoking device 600 and includes a housing 610. Within the housing 610 is a power source in the form of a battery 612 and control circuitry 614. Also within the housing is a liquid reservoir 620 containing a liquid aerosol-forming substrate that is vaporized to form an aerosol that is inhaled by the user. An atomizer assembly 630 is provided within the housing and coupled to the liquid reservoir 620. The atomizer assembly includes a vaporizer 634 (in this example, an electric heater) and a pump 632 positioned to pump liquid from the liquid reservoir 620 to the vaporizer 634. Both the pump 632 and the electric heater 634 are powered by the battery 612 under the control of the control circuitry 614, as will be described.

[0092] Housing 610 includes an air inlet 618 and an air outlet 616. Air outlet 616 is provided at the mouthpiece end of the housing. In use, a user inhales into the mouthpiece end of the housing. This draws air into the housing through air inlet 618, past vaporizer 634, and out through outlet 616 into the user's mouth. The air drawn past the vaporizer entrains vaporized aerosol-forming substrate. The vaporized aerosol-forming substrate cools as it travels through the device and into the user's mouth, forming an aerosol.

[0093] Activation of the heater may be controlled directly by the user pressing a button on the housing 610. Alternatively, the system may include an airflow sensor, such as a microphone 615, that detects airflow through the system, and the heater may be activated based on a signal from the airflow sensor. When a user draws air through the system (referred to herein as a puff), the airflow passes over the airflow sensor 615. If the airflow detected by the airflow sensor exceeds a threshold, the control circuit may activate the heater by supplying power to the heater. The control circuit may supply power to the heater for a predetermined period of time, or may supply power to the heater as long as the detected airflow exceeds a threshold. The control circuit may include a temperature sensing means, such as a dedicated temperature sensor or by monitoring the heater's electrical resistance. The control circuit may then supply power to the heater to raise its temperature within a desired temperature range. The temperature should be sufficient to vaporize the aerosol-forming substrate, but not so high that there is a significant risk of combustion.

[0094] The liquid in this example includes a mixture of water, glycerol, propylene glycol, nicotine, and flavoring. The liquid is held in a liquid reservoir 620. The liquid reservoir is provided as a cartridge that can be replaced when the liquid is depleted. To prevent leakage of the liquid both before and during use, the liquid reservoir has a housing formed from a rigid plastic material and is liquid-tight. As used herein, "rigid" refers to a housing that is self-supporting. In this example, the reservoir is formed by 3D printing using an acrylic-based photopolymer. The cartridge needs to be sturdy and be able to withstand significant loads during shipping and storage. However, because the liquid reservoir housing is sealed and rigid, the liquid reservoir has a fixed internal volume. The reduction in internal pressure within the liquid reservoir as the liquid is drawn by the pump can adversely affect the ability to pump the liquid out of the reservoir. To prevent a significant drop in pressure, the liquid reservoir has a pressure-equalizing air inlet valve 622. The pressure equalization valve 622 allows air to enter the liquid reservoir when the pressure difference between the interior of the reservoir and the exterior of the reservoir exceeds a threshold pressure difference.

[0095] The pump may be activated in the same manner as the heater. For example, the control circuit may provide power to the pump for the same period that power is provided to the heater. Alternatively, the control circuit may provide power to the pump for a period immediately following activation of the heater.

[0096] The control circuit 614 includes a feedback loop, as shown in FIG. 1, for controlling the pump 632. The pump 632 includes a piezoelectric transducer that drives a flexible diaphragm to vibrate. The vibration of the flexible diaphragm pushes the liquid aerosol-forming substrate out of the pump chamber through the outlet valve, decreasing the volume of the chamber, and sucks the liquid aerosol-forming substrate into the pump chamber through the inlet valve, increasing the volume of the chamber. To maximize pump efficiency, it is advantageous to operate the pump 632 at or near the resonant frequency of the transducer. However, as previously mentioned, the resonant frequency of the transducer may change for a number of reasons.

[0097] Changes in the resonant frequency of the transducer due to temperature changes, other environmental changes, or changes over time can be monitored and the drive signal modified accordingly using one of the feedback mechanisms described above.

[0098] A change in the resonant frequency of the transducer due to insufficient liquid being drawn into the pump chamber can be detected as a sudden change in resonant behavior, such as a change above a predetermined threshold between two measurement cycles. If a sudden change in resonant behavior is detected, operation of the pump and heater can be stopped until a new liquid reservoir is placed in the device.

Claims

1. An aerosol generating device, comprising: a piezoelectric transducer; a drive circuit connected to the piezoelectric transducer and configured to apply an oscillating current to the transducer; a control circuit connected to the drive circuit and configured to monitor the resonance behavior of the piezoelectric transducer, the control circuit configured to control operation of the drive circuit based on the resonance behavior of the piezoelectric transducer; An aerosol generating device, wherein the piezoelectric transducer forms part of a transducer assembly within a liquid pump, and the transducer assembly comprises a membrane or surface configured to contact a liquid aerosol-forming substrate, the transducer assembly being configured to vibrate the membrane or surface, the vibration of the membrane or surface forcing the liquid through an adjacent liquid valve within the liquid pump.

2. 2. The aerosol generating device of claim 1, wherein the control circuit is configured to control the operation of the drive circuit so that the oscillating current has a frequency equal to the resonant frequency of the piezoelectric transducer.

3. 2. The aerosol generating device of claim 1, wherein the control circuit is configured to control the operation of the drive circuit so that the oscillating current has a frequency that is shifted from the resonant frequency of the piezoelectric transducer.

4. An aerosol generating device as described in any one of claims 1 to 3, wherein the control circuit is configured to monitor the resonant behavior of the piezoelectric transducer at multiple resonant frequencies of the piezoelectric transducer corresponding to different modes of vibration.

5. An aerosol generating device as described in any one of claims 1 to 4, wherein the control circuit is configured to monitor the resonant behavior of the piezoelectric transducer by measuring the current delivered to the piezoelectric transducer or the impedance of the piezoelectric transducer.

6. 6. An aerosol generating device according to any one of claims 1 to 5, wherein the drive circuit and control circuit comprise a phase-locked loop (PLL).

7. 7. The aerosol generating device according to claim 1, wherein the piezoelectric transducer is an aerosol generating element configured to generate an aerosol from a liquid aerosol-forming substrate.

8. 8. The aerosol generating device of claim 7, wherein the piezoelectric transducer comprises a perforated plate.

9. 9. An aerosol generating device according to any one of claims 1 to 8, comprising a liquid reservoir containing a liquid aerosol-forming substrate, and in use the piezoelectric transducer comes into contact with liquid from the liquid reservoir.

10. 11. The aerosol generating device of claim 10, wherein the liquid comprises a mixture of different compounds.

11. 12. The aerosol generating device of claim 10 or claim 11, wherein the control circuit is configured to detect a reduction in the amount of liquid in contact with the piezoelectric transducer based on a change in the resonance behavior of the piezoelectric transducer.

12. 12. The aerosol generating device according to any one of claims 1 to 11, wherein the aerosol generating device is an e-cigarette.

13. 13. An aerosol generating device according to any one of claims 1 to 12, wherein the oscillating current comprises a first frequency modulated with at least one other frequency.

14. 1. A method of operating an aerosol generating device, the device comprising: a transducer assembly in a liquid pump, the transducer assembly comprising a piezoelectric transducer and a membrane or surface configured to contact a liquid aerosol-forming substrate, the piezoelectric transducer configured to vibrate the membrane or surface, the vibration of the membrane or surface forcing the liquid through an adjacent liquid valve in the liquid pump; a drive circuit connected to the piezoelectric transducer; and a control circuit connected to the drive circuit and configured to monitor a parameter of the piezoelectric transducer, the method comprising: applying an oscillating current to the transducer using the drive circuit; monitoring the resonant behavior of the piezoelectric transducer using the control circuit; and controlling the operation of the drive circuit based on the monitored resonance behavior of the piezoelectric transducer.

Images