AEROSOL-GENERATING DEVICE WITH FEEDBACK CONTROL OF TRANSDUCER

Abstract

An aerosol-generating device is provided, including: a piezoelectric transducer; drive circuitry connected to the piezoelectric transducer and configured to apply an oscillating current to the transducer; and control circuitry connected to the drive circuitry and configured to monitor a resonant behavior of the piezoelectric transducer, the control circuitry being further configured to control the operation of the drive circuitry based on the resonant behavior of the piezoelectric transducer, in which the piezoelectric transducer forms part of a transducer assembly in a liquid pump, and the transducer assembly includes a membrane or surface configured to contact a liquid aerosol-forming substrate, the transducer assembly being configured to drive the membrane or surface into vibration, the vibration of the membrane or surface forcing the liquid through an adjacent liquid valve in the liquid pump. A method of operating an aerosol generating device is also provided.

Claims

1-14. (canceled)

15. An aerosol-generating device, comprising: a piezoelectric transducer; drive circuitry connected to the piezoelectric transducer and configured to apply an oscillating current to the transducer; and control circuitry connected to the drive circuitry and configured to monitor a resonant behavior of the piezoelectric transducer, the control circuitry being further configured to control the operation of the drive circuitry based on the resonant behavior of the piezoelectric transducer, wherein the piezoelectric transducer forms part of a transducer assembly in 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 drive the membrane or surface into vibration, the vibration of the membrane or surface forcing the liquid through an adjacent liquid valve in the liquid pump.

16. The aerosol-generating device according to claim 15, wherein the control circuitry is further configured to control the operation of the drive circuitry so that the oscillating current has a frequency equal to a resonant frequency of the piezoelectric transducer.

17. The aerosol-generating device according to claim 15, wherein the control circuitry is further configured to control the operation of the drive circuitry so that the oscillating current has a frequency offset from a resonant frequency of the piezoelectric transducer.

18. The aerosol-generating device according to claim 15, wherein the control circuitry is further configured to monitor the resonant behavior of the piezoelectric transducer at a plurality of resonant frequencies of the piezoelectric transducer corresponding to different modes of vibration.

19. The aerosol-generating device according to claim 15, wherein the control circuitry is further configured to monitor the resonant behavior of the piezoelectric transducer by measuring a delivered power to the piezoelectric transducer or an impedance of the piezoelectric transducer.

20. The aerosol-generating device according to claim 15, wherein the drive circuitry and control circuitry comprise a phase locked loop (PLL).

21. The aerosol-generating device according to claim 15, wherein the piezoelectric transducer is an aerosol-generating element configured to generate an aerosol from a liquid aerosol-forming substrate.

22. The aerosol-generating device according to claim 21, wherein the piezoelectric transducer comprises a perforated plate.

23. The aerosol-generating device according to claim 15, further comprising a liquid reservoir containing a liquid aerosol-forming substrate, wherein, in use, the piezoelectric transducer is in contact with liquid from the liquid reservoir.

24. The aerosol-generating device according to claim 23, wherein the liquid comprises a mixture of different compounds.

25. The aerosol-generating device according to claim 23, wherein the control circuitry is further configured to detect reduction in an amount of the liquid in contact with piezoelectric transducer based on changes in the resonant behavior of the piezoelectric transducer.

26. The aerosol-generating device according to claim 15, wherein the aerosol-generating device is an e-cigarette.

27. The aerosol-generating device according to claim 15, wherein the oscillating current comprises a first frequency modulated with at least one other frequency.

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

Description

[0081] Examples will now be further described with reference to the figures in which:

[0082] FIG. 1 illustrates a feedback control system in accordance with the invention;

[0083] FIG. 2 is a schematic illustration of an aerosol generating device in accordance with the invention;

[0084] FIG. 3 illustrates a transducer assembly for use in the system of FIG. 2;

[0085] FIG. 4 is a schematic plot showing a change in response of the transducer over time;

[0086] FIG. 5 illustrates an example of a drive and control circuit implementing feedback control; and

[0087] FIG. 6 is a schematic illustration of a an aerosol-generating device comprising a piezoelectric pump in accordance with the invention.

[0088] FIG. 1 is a schematic illustration of a feedback control loop in accordance with the invention. The feedback loop comprises a transducer 12, driver circuitry 14 and control circuitry 14. The transducer in this example is a piezoelectric transducer. The transducer is coupled to and vibrates a membrane for generating an aerosol from a liquid supply. The transducer 12 is driven at a particular drive frequency by the drive circuitry 12. The drive circuitry 12 supplies an oscillating current to the transducer, which causes it to expand and contract. This in turn causes the membrane to vibrate.

[0089] The transducer has one or more resonant frequencies. The resonant frequencies depend on several factors including the load on the transducer. The load on the transducer depends on the properties of the membrane and any load on the membrane. The resonant frequencies also depend on temperature, for example.

[0090] In order to ensure that the transducer is being driven at a resonant frequency by the drive circuitry, the control circuitry 14 completes a feedback loop. The control circuitry receives a feedback parameter from the transducer, for example a phase shift or a vibration amplitude. The value of the feedback parameter varies depending on how close the drive frequency is to the resonant frequency of the transducer. The drive circuitry 12 adjusts the drive frequency of the oscillating current applied to the transducer 10 and the effect of that change in drive frequency on the feedback parameter is monitored by the control circuitry. The control circuitry then sends a control signal to the drive circuitry and the drive circuitry adjusts the frequency of the applied oscillating current based on the control signal, in order to achieve particular effect. In many cases it is desirable to drive the transducer as close to a resonant frequency as possible. But in some circumstances it may be desirable to drive the transducer at a particular offset from a resonant frequency or at a frequency between resonant and anti-resonant frequencies. The control circuitry may comprise filters, a microcontroller or any analog or digital means to process the feedback parameter in order generate the control signal.

[0091] FIG. 2 is a schematic view of a first embodiment of an aerosol-generating device according to the invention, that incorporates the feedback control illustrated in FIG. 1. FIG. 2 is schematic in nature. In particular, the components shown are not necessarily to scale either individually or relative to one another. The aerosol-generating device comprises a reusable device portion 100 in cooperation with a cartridge 200, which is preferably disposable. In FIG. 2, the device is an electrically operated smoking system.

[0092] The device portion 100 comprises a main body having a housing 101. The housing 101 is substantially circularly cylindrical and has a longitudinal length of about 100 mm and an external diameter of about 20 mm, comparable to a conventional cigar. In the device, there is provided an electric power supply in the form of battery 102 and electric control circuitry 104. The electric control circuitry 104 includes the drive circuitry and control circuitry for the transducer, as described with reference to FIG. 1. The main body housing 101 also defines a cavity 112 into which the cartridge 200 is received.

[0093] The cartridge 200 (shown in schematic form in FIG. 2) comprises a rigid housing defining a liquid storage portion 201. The liquid storage portion 201 holds a liquid aerosol-forming substrate (not shown). The housing of the cartridge 200 is fluid impermeable but has an open end (not shown) that is coverable by a removable lid (not shown) when the cartridge is removed from the device 100. The lid may be removed from the cartridge 200 before insertion of the cartridge into the device. The cartridge 200 includes keying features (not shown) to ensure the cartridge 200 cannot be inserted into the device upside—down.

[0094] The device portion 100 also includes a mouthpiece portion 120. The mouthpiece portion 120 is connected to the main body housing 101 by a hinged connection in this example, but any kind of connection may be used, such as a snap fitting or a screw fitting. The mouthpiece portion 120 comprises a plurality of air inlets 122, an air outlet 124 and an aerosol forming chamber 125, and an atomiser 300 mounted therein (shown schematically in FIG. 2). Air inlets 122 are defined between the mouthpiece portion 120 and the main body housing 101 of the device 100 when the mouthpiece portion is in a closed position, as shown in FIG. 2. An air-flow route 127 is formed from the air inlets 122 to the air outlet 124 via the aerosol forming chamber 125 and the atomiser 300, as shown in FIG. 2 by the arrows.

[0095] As shown in FIG. 3, the atomiser 300 comprises a vibratable element 301 and transducer 302 housed inside an atomiser housing 304. Atomiser housing 304 comprises a hollow cylindrical box, having an inlet opening 305 and an outlet opening 306 arranged in co-axial alignment at opposite sides of the housing 304. The housing 304 is removably connected to the mouthpiece 120 of the device portion 100 by a screw thread connection (not shown). A male screw thread (not shown) is provided at an outer surface of the atomiser housing 304, that is complimentary to a female screw thread (not shown) on an inner surface of the mouthpiece 120. Atomiser 300 is removable from the mouthpiece portion 120 of the device portion for disposal or for cleaning.

[0096] Vibratable element 301 comprises a substantially circular aluminium disc, having a thickness of about 2 mm and a diameter of about 15 mm.

[0097] A plurality of passages 303 extends from an inlet side 308 to an opposing outlet side 309 of the vibratable element. 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 arranged substantially centrally in the element 301.

[0098] The passages (not shown) have a substantially circular cross-section and are tapered from the inlet side 308 to the outlet side 309 of the vibratable element 301. The passages have a diameter at the inlet side of about 8 μm and a diameter at the outlet side of about 6 μm. The passages are typically formed by high-speed laser drilling. The plurality of passages is comprised of about 4000 passages arranged with equal spacing across the array.

[0099] Transducer 302 comprises a piezoelectric transducer. The piezoelectric transducer is a substantially circular annular disc of piezoelectric material, typically 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.

[0100] As shown in FIG. 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 circumscribes 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. In other embodiments (not shown) it is envisaged that the piezoelectric transducer 302 may be in direct contact with the vibratable element 301 at the inlet side 308.

[0101] The vibratable element 301 and piezoelectric transducer 302 are supported within the atomiser housing 304 by a pair of elastomeric O-rings 311, which allow the vibratable element 301 and the 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 the piezoelectric transducer 302 may be bonded by any suitable means, such as an adhesive layer.

[0102] The vibratable element 301 and the piezoelectric transducer 302 are arranged within the atomiser housing 304 such that the array of passages 303 is in coaxial alignment with the inlet and outlet openings 305, 306 of the housing 304.

[0103] One or more spring pins 310 extend through an opening 312 in the atomiser housing 304 to provide electrical connection of the piezoelectric transducer 302 to the control circuitry 104 and the 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 by a mechanical connection so that good electrical contact is maintained during vibration of the piezoelectric transducer 302.

[0104] In use, when the atomiser 300 is removably connected to the mouthpiece portion 120 of the device portion 100 and the cartridge 200 is received in the cavity 112 of the device, an elongate capillary body (not shown in FIG. 2) extends from the liquid storage portion 201 of the cartridge 200 to the atomiser 300 to fluidly connect the cartridge 200 to the atomiser 300. As shown in FIG. 3, the elongate capillary body 204 extends into the atomiser housing 304 and abuts the inlet side 308 of the vibratable element 301 at the array of passages 303. Heating means is provided in the liquid storage portion in the form of a coil heater 205 surrounding the capillary body 204. Note that the coil heater is only shown schematically in FIG. 3. The coil heater 205 is connected to the electric circuitry 104 and battery 102 of the device 100 via connections (not shown), which may pass along the outside of the liquid storage portion 200, although this is not shown in FIG. 2 or FIG. 3.

[0105] In use, liquid aerosol-forming substrate (not shown) is conveyed by capillary action from the liquid storage portion 201 from the end of the capillary body 204 which extends into the liquid storage portion 201, past the heater coil 205, and to the other end of the capillary body 204, which extends into the atomiser housing 304 and abuts the vibratable element 301 at the inlet side 308 at the array of passages 303.

[0106] When a user draws on the air outlet 124 of the mouthpiece portion 120, ambient air is drawn through air inlets 122. In the embodiment of FIG. 2, a puff detection device 106 in the form of a microphone, is also provided as part of the control electronics 104. A small air flow is drawn through a sensor inlet 121 in the main body housing 101, past the microphone 106 and up into the mouthpiece portion 120. When a puff is detected by the electric circuitry 104, the electric circuitry 104 activates the heater coil 205 and the piezoelectric transducer 302. The battery 102 supplies electrical energy to the coil heater 205 to heat the capillary body 204 surrounded by the coil heater.

[0107] The battery 102 further supplies electrical energy to the piezoelectric transducer 302, under the control of the drive and control circuitry, which vibrates, deforming in the thickness direction. The piezoelectric transducer 302 typically vibrates at around approximately 150 kHz. The drive current supplied to the transducer has an initial frequency and wave shape based on parameters stored in memory. During manufacture of the device the frequency response of the transducer assembly, including the vibratable element 301, can be characterised and an initial frequency and waveform set. The piezoelectric transducer 302 transmits the vibrations to the vibratable element 301, which vibrates, also deforming in the thickness direction. An LED 108 is also activated to indicate that the device is activated. As will be described, during operation the feedback control loop is used to adjust the drive current supplied to the transducer in response to detected changes in resonant behaviour.

[0108] The coil heater 205 heats the liquid aerosol-forming substrate being conveyed along the capillary body, past the coil heater 205, to a predetermined temperature of about 45° C.

[0109] The vibrations in 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 at the inlet side 308 of the vibratable element 301, and ejects atomised droplets of liquid aerosol-forming substrate from the passages at the outlet side 309 of the vibratable element 301, forming an aerosol. At the same time, the heated liquid being atomised is replaced by further liquid moving along the capillary body 204 by capillary action. (This is sometimes referred to as ‘pumping action’). The aerosol droplets ejected from the vibratable element 301 mix with and are carried in the air flow 127 from the inlets 122 in the aerosol forming chamber 125, and are carried towards the air outlet 124 of the mouthpiece 120 for inhalation by the user.

[0110] As previously described, during operation the resonant response of the transducer may change. FIG. 4 is a schematic plot of a sensed parameter from the transducer, showing a change in frequency over time. The distance in time between successive crossings of the signal through zero is a measure of frequency and may be used to synchronize the driving signal with the working frequency of the transducer, in this example its resonant frequency. The signal may be, for example, the current measured by a sense resistor in series with the transducer. In that case the amplitude may have a unit of Amperes for the current or the amplitude may be normalized, for example by its maximum value, in which case the unit of the amplitude is 1. Time may have, for example, the unit of milliseconds or microseconds depending on the characteristic frequency working range covered by the transducer.

[0111] One specific example of a possible implementation of such a feedback loop is shown in FIG. 5. The transducer 500, which is connected to the vibratable perforated plate in the embodiment of FIG. 3, is driven by a half-bridge 505, consisting of two power MOSFETs 510, 515. An optional series inductor 520, for example a 10 microhenrys inductor, may be used between the half-bridge and the transducer to tune impedance. The current sense resistor 525, of for example 1 Ohm, may be placed at the low end 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 filter and gain stage 530. The filter and gain stage 530 may comprise, for example, a low pass filter, in order to cut off high frequency harmonics, and an FET amplifier, for example AD823, to amplify the signal. A comparator 540 creates the feedback signal, in this example a square wave signal as an appropriate input waveform for the gate driver 550. The gate driver 550 may, for example, be an IC of type LT1162, and drives the half-bridge 505. As the change in frequency is detected and sent back to the driver, the transducer 500 will be driven always at its working frequency, for example its resonant frequency. The drive and control circuitry shown in FIG. 5 can be incorporated into the control circuitry 104 shown in FIG. 2.

[0112] FIG. 6 is an illustration of an aerosol-generating device according to another embodiment of the present invention. FIG. 6 is schematic in nature. In particular, the components shown are not necessarily to scale either individually or relative to one another. The device of FIG. 6 generates 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.

[0113] The device is a handheld, electrically operated smoking device 600 and comprises a housing 610. Within the housing 610 there is an electric power supply in the form of battery 612 and control circuitry 614. Also within the housing there is a liquid reservoir 620 containing a liquid aerosol-forming substrate that is vapourised in order to form an aerosol that is inhaled by a user. An atomiser assembly 630 is provided within the housing, coupled to the liquid reservoir 620. The atomiser assembly comprises a vapouriser 634, in this example an electrical heater, and a pump 632 positioned to pump liquid from the liquid reservoir 620 to the vapouriser 634. Both the pump 632 and the electric heater 634 are provided with power from the battery 612 under the control of the control circuitry 614, as will be described.

[0114] The housing 610 includes an air inlet 618 and an air outlet 616. The air outlet 616 is provided at a mouthpiece end of the housing. In use, a user sucks on the mouthpiece end of the housing. This draws air through the air inlet 618 into the housing, past the vapouriser 634 and out through the outlet 616 into the user's mouth. The air drawn past the vapouriser entrains vapourised aerosol-forming substrate. The vapourised aerosol-forming substrate cools to form an aerosol as it moves through the device and into the user's mouth.

[0115] Activation of the heater may be controlled directly by a user pressing a button on the housing 610. Alternatively, the system may comprise an airflow sensor, such as a microphone 615, that detects airflow through the system and the heater may be activated based on signals from the airflow sensor. When a user draws air through the system, herein referred to as puffing, air flows past the air flow sensor 615. If the airflow detected by the airflow sensor exceeds a threshold value, then the control circuitry may activate the heater by supplying power to the heater. The control circuitry may supply power to the heater for a predetermined time period or may supply power to the heater for as long as the detected airflow exceeds a threshold. The control circuitry may include temperature sensing means, such as a dedicated temperature sensor or by monitoring an electrical resistance of the heater. The control circuitry may then supply power to the heater to raise the temperature of the heater to within a desired temperature range. The temperature should be sufficient to vapourise the aerosol-forming substrate but not so high that there is a significant risk of combustion.

[0116] The liquid in this example comprises a mixture of water, glycerol, propylene glycol, nicotine and flavourings. The liquid is held within the liquid reservoir 620. The liquid reservoir is provided as a cartridge that can be replaced when the liquid has been used up. In order to prevent leakage of the liquid, both before and during use, the liquid reservoir has a housing formed from a rigid plastics material, and is liquid tight. As used herein “rigid” means that the 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 robust and 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. A reduction in the internal pressure inside the liquid reservoir as liquid is removed by the pump, could detrimentally affect the ability to pump liquid out of the reservoir. In order to prevent a significant drop in pressure, the liquid reservoir has an equalising air inlet valve 622. The equalising valve 622 allows air into the liquid reservoir when the pressure difference between the inside the reservoir and outside of the reservoir exceeds a threshold pressure difference.

[0117] The pump may be activated in the same way as the heater. For example the control circuitry may supply power to the pump for the same time periods as power is supplied to the heater. Alternatively, the control circuitry may supply power to the pump in periods immediately following activation of the heater.

[0118] The control circuitry 614 includes a feedback loop as illustrated in FIG. 1 for control of the pump 632. The pump 632 includes a piezoelectric transducer that drives a flexible diaphragm to vibrate. Vibration of the flexible diaphragm pushes liquid aerosol-forming substrate out of a pump chamber through an outlet valve as it reduces the chamber volume, and draws liquid aerosol-forming substrate into the pump chamber through an inlet valve as it increase chamber volume. In order maximise pumping efficiency, it is advantageous to operate the pump 632 at or close to a resonant frequency of the transducer. However, as previously described, the resonant frequency of the transducer may change for a number of reasons.

[0119] Changes in the resonant frequency of the transducer due to temperature changes, other environmental changes or aging can be monitored and the drive signal modified accordingly using one of the feedback mechanisms described above.

[0120] Change to 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 behaviour, such as a change greater than a predetermined threshold between two measurement cycles. If a sudden change in resonant behaviour is detected, operation of the pump and the heater can be stopped until a new liquid reservoir is placed in the device.