AEROSOL-GENERATING DEVICE USING VIBRATING TRANSDUCER AND CONTROLLED LIQUID SUPPLY

Abstract

An aerosol-generating device is provided, including: a reservoir containing a liquid aerosol-forming substrate; an aerosol-generating element configured to generate an aerosol from the liquid aerosol-forming substrate, the aerosol-generating element including an electrically operated, vibrating transducer; an electrically operated pump configured to deliver the liquid aerosol-forming substrate from the reservoir to the aerosol-generating element; and control circuitry connected to the pump and the transducer, the control circuitry being configured to control operation of the pump in dependence on one or more operating parameters of the transducer. A method of operating the aerosol-generating device is also provided.

Claims

1.-15. (canceled)

16. An aerosol-generating device, comprising: a reservoir containing a liquid aerosol-forming substrate; an aerosol-generating element configured to generate an aerosol from the liquid aerosol-forming substrate, the aerosol-generating element comprising an electrically operated, vibrating transducer; an electrically operated pump configured to deliver the liquid aerosol-forming substrate from the reservoir to the aerosol-generating element; and control circuitry connected to the pump and the transducer, the control circuitry being configured to control operation of the pump in dependence on one or more operating parameters of the transducer.

17. The aerosol-generating device according to claim 16, wherein the control circuitry is further configured to control a rate of delivery of liquid from the reservoir to the aerosol-generating element in dependence on one or more operating parameters of the transducer.

18. The aerosol-generating device according to claim 16, wherein the control circuitry is further configured to drive the transducer.

19. The aerosol-generating device according to claim 16, wherein the one or more operating parameters comprises one or more of: a drive voltage, a drive current, a resonant frequency, an impedance, a phase difference, a drive frequency, a rate of change of impedance, a rate of change of current, and a rate of change of voltage.

20. The aerosol-generating device according to claim 16, wherein the control circuitry is further configured to receive a feedback signal from the transducer and to control the operation of the pump in dependence on the feedback signal.

21. The aerosol-generating device according to claim 20, wherein the feedback signal comprises one or more of: a resonant frequency, an impedance, and a phase.

22. The aerosol-generating device according to claim 20, wherein the control circuitry is further configured to periodically control the operation of the pump in dependence on the feedback signal.

23. The aerosol-generating device according to claim 20, wherein the control circuitry is further configured to compare the feedback signal with one or more thresholds to provide a comparison result and to alter operation of the pump in dependence on the comparison result.

24. The aerosol-generating device according to claim 23, wherein the control circuitry is further configured to alter the operation of the pump if the feedback signal is not a desired value or within a desired range of values.

25. The aerosol-generating device according to claim 20, wherein the control circuitry is further configured to control the transducer based on the feedback signal.

26. The aerosol-generating device according to claim 16, wherein the aerosol-generating element is further configured to be controlled by the control circuitry to operate in different modes of vibration.

27. The aerosol-generating device according to claim 16, further comprising a sensor connected to the control circuitry, wherein the control circuitry is further configured to control the one or more operating parameters of the transducer dependent on an output from one or more sensors.

28. The aerosol-generating device according to claim 16, further comprising a mouthpiece through which a user can draw generated aerosol.

29. A method of operating an aerosol-generating device, the aerosol-generating device comprising a liquid reservoir, an aerosol generating element configured to generate an aerosol from a liquid aerosol-forming substrate, the aerosol generating element comprising an electrically operated, vibrating transducer, and an electrically operated pump configured to deliver liquid from the liquid reservoir to the aerosol generating element, the method comprising: controlling operation of the pump in dependence on one or more operating parameters of the transducer.

30. The method according to claim 29, wherein the step of controlling comprises controlling a rate of liquid delivery from the reservoir to the aerosol-generating element in dependence on the one or more operating parameters of the transducer.

Description

[0115] Examples will now be further described with reference to the figures, in which:

[0116] FIG. 1 is a schematic of an aerosol-generating device in accordance with the disclosure;

[0117] FIG. 2 illustrates delivery of liquid to a vibrating plate transducer;

[0118] FIG. 3 is a schematic illustration of feedback control used in an embodiment of the disclosure;

[0119] FIG. 4 is a schematic illustration of feedback control used in an embodiment of the disclosure;

[0120] FIGS. 5a and 5b illustrate the behaviour of a transducer under different liquid loads;

[0121] FIG. 6 illustrates a measurement circuit for providing a measure of impedance and phase of a transducer for feedback;

[0122] FIG. 7 illustrates feedback signals based on impedance and current; and

[0123] FIG. 8 illustrates the behaviour of a transducer over time under variable liquid load.

[0124] FIG. 1 is a schematic of an aerosol-generating device comprising a pump and an aerosol-generating element. The aerosol-generating device 10 is a handheld vaporiser with a mouthpiece 12 through which generated aerosol can be inhaled by a user. The device comprises a housing 20 containing a power source 22 and control unit 24, a micropump 26, an transducer assembly 28 including an aerosol-generating element and a vibrating transducer, and user interface components 30 including an airflow sensor and at least one input button. A cartridge 32 containing a liquid aerosol-forming substrate, is received in the device, from which the micropump can deliver liquid aerosol-forming substrate to the transducer assembly 28.

[0125] The power source 22 is a rechargeable lithium ion battery. The battery is connected to the control unit 24 and provides power to both the micropump 26 and the transducer assembly 28 through the control unit. The control unit 24 comprises control circuitry 25, a pump drive circuit 27 and a transducer drive circuit 29. The control circuitry 25 may include a memory and a controller, for example, a field-programmable gate array (FPGA) or a programmable microcontroller (MCU). The characteristics of the vibrating transducer and micropump are stored in the memory and read out during operation.

[0126] The micropump may be may be a mechanical pump, a diaphragm pump, a piezoelectric pump, a peristaltic pump, an electro-hydrodynamic or magneto-hydrodynamic pump, an electro-osmotic pump, an adhesion pump, or rotary pump. An example of a suitable micropump is the mp6 micropump from Bartels Mikrotechnik GmbH, Konrad-Adenauer-Allee 11, 44263 Dortmund, Germany, which uses a piezoelectric diaphragm in combination with passive check valves.

[0127] The aerosol-generating element comprises a piezoelectric transducer that drives a perforated plate. FIG. 2 illustrates the arrangement of the transducer and plate. As shown in FIG. 2, the transducer assembly 28 comprises a vibratable plate 100 and transducer 102 housed inside an aerosol generator housing 104. The housing 104 comprises a hollow cylindrical box, having an inlet opening 105 and an outlet opening 106 arranged in co-axial alignment at opposite sides of the housing 104.

[0128] The vibratable plate 100 comprises a substantially circular aluminium disc, having a thickness of about 2 mm and a diameter of about 15 mm. A plurality of perforations 103 extends from an inlet side 108 to an opposing outlet side 109 of the vibratable plate. The plurality of perforations 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 plate 100.

[0129] The perforations have a substantially circular cross-section and are tapered from the inlet side 108 to the outlet side 109 of the vibratable plate 100. The passages have a diameter at the inlet side of about 8 ?m and a diameter at the outlet side of about 6 ?m. The perforations are typically formed by high-speed laser drilling. The plurality of perforations is comprised of about 4000 perforations arranged with equal spacing across the array.

[0130] Transducer 102 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.

[0131] As shown in FIG. 2, the transducer 102 is in direct contact with the vibratable plate 100, at the outlet side 109 of the vibratable plate. The inner diameter of the piezoelectric transducer 102 circumscribes the array of perforations 103, such that the open ends of the perforations at the outlet side are not covered by the piezoelectric transducer 102. In other embodiments (not shown) it is envisaged that the piezoelectric transducer 102 may be in direct contact with the vibratable plate 100 at the inlet side 108.

[0132] The vibratable plate 100 and piezoelectric transducer 102 are supported within the housing 104 by a pair of elastomeric O-rings 111, which allow the vibratable plate 100 and the piezoelectric transducer 102 to vibrate within the housing 104. The vibratable plate 100 and piezoelectric transducer 102 are held together by pressure from the opposing O-rings 111. However, in other embodiments (not shown) the vibratable plate 100 and the piezoelectric transducer 102 may be bonded by any suitable means, such as an adhesive layer.

[0133] The vibratable plate 100 and the piezoelectric transducer 102 are arranged within the housing 104 such that the array of perforations 103 is in coaxial alignment with the inlet and outlet openings 105, 106 of the housing 104.

[0134] One or more spring pins 110 extend through an opening 112 in the housing 104 to provide electrical connection of the piezoelectric transducer 102 to the control circuitry and the battery of the device. The one or more spring pins 110 are held in contact with the piezoelectric transducer 102 by pressure, rather than by a mechanical connection so that good electrical contact is maintained during vibration of the piezoelectric transducer 102.

[0135] In use, the micropump 26 delivers liquid from the liquid reservoir to the perforated plate 100. As shown in FIG. 3, a liquid delivery tube 114 extends into the housing 104 and ends adjacent to the inlet side 108 of the plate 100 at the array of perforations 103. In use, liquid aerosol-forming substrate (not shown) is delivered by the pump through the liquid delivery tube 114.

[0136] The device includes at least one air inlet 16 in the housing, an air outlet 14 through the mouthpiece and an airflow path that extends from the air inlet 14 to the air outlet 16 past the aerosol generating element. When a user draws on the mouthpiece air is drawn through the air inlet, past the vibratable plate 100 to the air outlet.

[0137] The user interface components 30 include an airflow sensor. The airflow sensor may be any suitable airflow sensor, such as a microphone. When a user draws on the air outlet of the mouthpiece, ambient air is drawn through air inlet. The airflow sensor is positioned to detect this airflow. When an airflow indicative of a user puff is detected by the airflow sensor, the control unit 24 activates the piezoelectric transducer 102 and the micropump 26. The battery supplies electrical energy to the piezoelectric transducer 102, under the control of the control unit 24, which vibrates, deforming in the thickness direction. The piezoelectric transducer 102 transmits the vibrations to the vibratable plate 100, which vibrates, also deforming in the thickness direction. The vibrations in the vibratable plate 100 deform the plurality of perforations 103, which draws liquid aerosol-forming substrate from the delivery tube 114, through the plurality of perforations 103 at the inlet side 108 of the vibratable plate 100, and ejects atomised droplets of liquid aerosol-forming substrate from the passages at the outlet side 109 of the vibratable plate 100, forming an aerosol. The aerosol droplets ejected from the vibratable plate 100 mix with and are carried in the air flow from the inlet and are carried towards the air outlet 124 for inhalation by the user.

[0138] The user interface components may comprise an on/off button, so that the device must be switched on before the power can be supplied to the micropump or transducer. The user interface components may also include an interface that allows a user to select different operating modes or settings.

[0139] The control of the micropump and transducer is coordinated by the control unit. A first embodiment of a control scheme is shown in FIG. 3. FIG. 3 illustrates the control circuitry 25 connected to both a pump drive circuit 27 and a transducer drive circuit 29. The pump drive circuit 27 is connected to the pump 26 and the transducer drive circuitry 29 is connected to the transducer 102. In this embodiment the operating parameters of the transducer 102 are determined based on input from the airflow sensor 30 and on information stored in memory. 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 plate 100, can be characterised and an initial frequency and waveform set. The control circuitry 25 controls the transducer drive circuit to control the current supplied to the transducer and the pump drive circuitry to control the current supplied to the micropump. The drive current supplied to the transducer can then be modified based on the strength of the detected airflow. A higher detected airflow rate may give rise to a higher frequency or higher amplitude current being supplied to the transducer from the transducer drive circuit 29 in order to generate a greater volume of aerosol. The control circuitry 25 controls the pump drive circuit based on the parameters being applied to the transducer drive circuit. If a greater current is being supplied to the transducer to generate a particular throughput of aerosol, the corresponding pump parameters may be read from memory and the pump drive circuit controlled accordingly to ensure a matching amount of liquid is delivered to the aerosol generating element.

[0140] In another embodiment the control unit may receive a signal feedback from the transducer indicating the condition of the transducer, for example whether there is enough, not enough or too much liquid on the transducer. This arrangement is illustrated in FIG. 4. FIG. 4 again illustrates the control circuitry 25 connected to both a pump drive circuit 27 and a transducer drive circuit 29. The pump drive circuit 27 is connected to the pump 26 and the transducer drive circuitry 29 is connected to the transducer 102. However, in the arrangement of FIG. 4 a feedback signal from the transducer is provided to the control circuitry. The feedback signal indicates the state of the load on the transducer, and may be, for example, resonance frequency, impedance or phase. The load on the transducer depends on how much liquid is present at the perforated plate 100. So the feedback signal is indicative of whether there is enough, not enough or too much liquid at the perforated plate.

[0141] FIGS. 5a and 5b illustrate the behaviour of a transducer under different liquid loads that can form the feedback signal. FIG. 5a shows the impedance over a frequency range covering the transducer's main resonance peak. The solid line shows the impedance with no load on the transducer, the dashed line shows impedance for liquid load under normal operating conditions to generate aerosol, and the dash-dotted line shows the impedance for too much liquid on the perforated plate, which might occur if the pump is supplying too much liquid. It can be seen that the pump impedance can be used as an indicator of liquid conditions at the perforated plate. FIG. 5b shows the phase of the transducer over the same frequency range. Again the solid line shows the phase with no liquid on the transducer, the dashed line shows phase for liquid load under normal operating conditions to generate aerosol, and the dash-dotted line shows the phase for too much liquid on the perforated plate. For a fixed operating frequency, the phase angle decreases with increasing liquid load and may turn the reactance of the transducer capacitive. Increasing liquid load also lowers the resonance frequency of the transducer.

[0142] Providing a feedback signal indicative of the load on the perforated plate allows the control circuitry to adjust the control of the pump to avoid overloading or under loading. The feedback signal can be provided to the control circuitry continuously. There are various methods that can be employed for measurement of impedance, phase and frequency. For example, bridge circuits, such as a Wheatstone bridge, integrated circuits such as AD5941 and CD4040, phase comparator or phase frequency detectors based on logic gates, or an SoC, for example Xilinx Zynq 710. FIG. 6 illustrates a measurement circuit for providing a measure of impedance and phase of a transducer for feedback. The transducer is illustrated by dashed box 200 as comprising a resistance and R.sub.T and a reactance X.sub.T. A series resistor 210 is used to measure the current flow into the transducer. A voltage V.sub.S having a fixed frequency and amplitude is applied by the transducer drive circuit and the voltage across the transducer V.sub.T and across the resistor V.sub.R are measured. This allows for the calculation of the impedance Z.sub.T of the transducer and the phase ?=arc tan (X.sub.T/R.sub.T).

[0143] The control circuitry uses the feedback signal to alter the current or voltage applied to the pump by the pump drive circuit. FIG. 7 illustrates feedback signals based on impedance and current. The impedance over time is shown as the solid line. The corresponding current is shown as a dotted line. The current under stable load conditions, on the right side of FIG. 7 is around 40 mA. Current increases as load decreases. So the control circuitry may be configured to detect when a threshold of current is reaches, say 50 mA, indicating too little liquid is being supplied. So, as shown in FIG. 7, initially there is too little liquid being delivered and the current is above the 50 mA threshold. The control circuitry increases the supply of liquid from the pump until the stable conditions are reached. The monitoring of the feedback signal and the comparison to a threshold or thresholds can be carried out on a continuous basis during operation of the transducer.

[0144] A similar control can be based on impedance as illustrated by FIG. 7, with impedance thresholds used in the same way as current thresholds. In the example shown in FIG. 7, the load impedance in stable conditions is in the range of 420 Ohms to 470 Ohms. Whenever the impedance is outside of a window, for example falling below 400 Ohms or above 500 Ohms, the control circuitry sends modified driving parameters to the pump drive circuit to maintain stable aerosol generation, or alternatively to stop aerosol generation.

[0145] If the control circuitry stops aerosol generation based on the feedback signal, the pump drive signal is stopped first. After a predetermined time period, the transducer drive signal is stopped. This ensures that liquid already at the transducer is turned into aerosol and is not replaced with more liquid. This reduces the possibility of liquid leaking from the device after the device has stopped operating.

[0146] As an alternative to using fixed thresholds, the rate of change of impedance, current or phase can be monitored by the control circuitry to determine how to modify the pump drive signal or the transducer drive signal. Changes in impedance greater than a predetermined amount in a predetermined time period can indicate unstable conditions at the aerosol generating element.

[0147] FIG. 8 illustrates how phase provides a feedback signal indicative of the load on the transducer over time. FIG. 8 shows the phase and current over time of a transducer operated at a fixed frequency and voltage. The supply of liquid to the transducer from the pump is set too low for the rate of aerosol generation by the transducer. The mismatch between the transducer throughput and the pump flow rate leads to discontinuous aerosol generation. The liquid applied to the transducer is quickly turned into aerosol and there is then a delay before sufficient liquid is delivered. While the transducer is unloaded the phase angle is large and positive. When liquid is added, the phase angle steeply drops. In this example, the transducer takes only around 0.4 seconds to become unloaded again. Using phase angle, the control circuitry can adjust the operation of the pump to deliver liquid at a higher rate, providing steady state conditions at the transducer. Using phase as a feedback signal has an advantage that it is not significantly affected by changes in the magnitude of the voltage applied to the transducer.

[0148] The feedback signal may also be used to determine the drive signal provided to the transducer. For example, if there is decrease in liquid load detected the drive signal to the transducer can be altered to reduce throughput and balance throughput with the delivery rate of the pump. The system is able to both provide a variable rate of aerosol generation to meet a user's needs and stable load conditions at the aerosol generating element.

[0149] It may also be useful to tune the driving frequency of the transducer based on the feedback signal in order optimise efficiency. If the transducer impedance is matched to the impedance of the transducer drive circuit power efficiency can be maximised. As the impedance of the transducer changes with changing load conditions, the feedback signal can be used to modify the driving frequency of the transducer so as to maintain the same impedance.