Source: http://patents.com/us-9713345.html
Timestamp: 2017-12-15 04:29:01
Document Index: 185473278

Matched Legal Cases: ['Application No. 10', 'Application No. 2015', 'Application No. 2015', 'Application No. 10', 'Application No. 201380047266', 'Application No. 102132555', 'Application No. 2015113364', 'Application No. 201510908619', 'Application No. 12183837']

US Patent # 9,713,345. Device and method for controlling an electrical heater to limit temperature - Patents.com
United States Patent 9,713,345
Farine , et al. July 25, 2017
Device and method for controlling an electrical heater to limit temperature
There is provided a method of controlling an electrical heating element, including maintaining a temperature of the heating element at a target temperature by supplying pulses of electrical current to the heating element; monitoring a duty cycle of the pulses of electrical current; and determining if the duty cycle differs from an expected duty cycle or range of duty cycles, and if so, reducing the target temperature, or stopping the supply of current to the heating element or limiting the duty cycle of the pulses of electrical current supplied to the heating element. As the temperature is maintained at a known target temperature, any variation in the duty cycle or range of duty cycles expected to maintain the target temperature is indicative of abnormal conditions.
Farine; Robin (Auvernier, CH), Talon; Pascal (Thonon-les-Baines, FR)
Family ID: 1000002726973
14/427,093
PCT/EP2013/068722
WO2014/040988
US 20150237916 A1 Aug 27, 2015
Sep 11, 2012 [EP] 12183837
Current CPC Class: A24F 47/008 (20130101); G05D 23/1917 (20130101); G05D 23/1919 (20130101); H05B 1/0225 (20130101); H05B 1/0244 (20130101)
Current International Class: H05B 1/02 (20060101); A24F 47/00 (20060101); G05D 23/19 (20060101)
Field of Search: ;219/492,497,501,505,483 ;131/328,329,330,273,194
6833535 December 2004 Streit
6870142 March 2005 Hada
6968842 November 2005 Truschel
7167776 January 2007 Maharajh
7400942 July 2008 Cheng
2013/0164191 June 2013 Coursey
2013/0233170 September 2013 Spiegelman
2 084 229 Mar 1994 CA
2 391 688 Oct 2003 CA
1481525 Mar 2004 CN
1491525 Apr 2004 CN
101093723 Dec 2007 CN
101522244 Sep 2009 CN
101883596 Nov 2010 CN
102022245 Apr 2011 CN
102081416 Jun 2011 CN
102595943 Jul 2012 CN
438862 Jul 1991 EP
2 253 233 Nov 2010 EP
2 468 118 Jun 2012 EP
2001-502542 Feb 2001 JP
10-0838859 Jun 2008 KR
10-2010-0127817 Dec 2010 KR
10-2010-0135865 Dec 2010 KR
2 411 047 Sep 2010 RU
WO 02/051468 Jul 2002 WO
WO 2008/108889 Sep 2008 WO
WO 2012/085205 Jun 2012 WO
Office Action issued Dec. 10, 2015 in Korean Patent Application No. 10-2015-7008464. cited by applicant .
International Preliminary Report on Patentability and Written Opinion issued Mar. 26, 2015 in PCT/EP2013/068722. cited by applicant .
Communication Relating to the Results of the Partial International Search issued Dec. 15, 2014 in PCT/EP2013/068722 Filed Sep. 10, 2013. cited by applicant .
English translation of Office Action issued on Feb. 15, 2016 in Japanese Patent Application No. 2015-223869. cited by applicant .
English translation of Office Action issued on Feb. 10, 2016 in Japanese Patent Application No. 2015-531539. cited by applicant .
Notice of Allowance issued Jun. 20, 2016 in Korean Patent Application No. 10-2016-7000339 (with partial English translation). cited by applicant .
Combined Chinese Office Action and Search Report issued Jun. 14, 2016 in Patent Application No. 201380047266.5 (submitting English translation only). cited by applicant .
English Translation only of Notification for the Opinion of Examination Intellectual Property Office Ministry of Economic Affairs mailed on Nov. 3, 2016 in corresponding Taiwanese Application No. 102132555, filed on Sep. 10, 2013, (10 pages). cited by applicant .
English Translation only of Russian Office Action with Search Report dated Sep. 15, 2016 in corresponding Russian Application No. 2015113364, filed on Sep. 10, 2013, (5 pages). cited by applicant .
Russian Search Report in English only, search completed on Dec. 2, 2016, (2 pages). cited by applicant .
English translation of "Notification of the First Office Action" dated Mar. 15, 2017 in counterpart Chinese Application No. 201510908619.7, 7 pages, citing documents AO through AS therein. cited by applicant.
1. A method of controlling an electrical heating element, comprising: maintaining a temperature of the heating element at a target temperature by supplying pulses of electrical current to the heating element; monitoring a duty cycle of the pulses of electrical current by determining a proportion of time that electrical current is supplied to the heating element, to provide a detected duty cycle; and comparing the detected duty cycle with an expected duty cycle to determine if the detected duty cycle differs from the expected duty cycle or range of duty cycles, and if so, reducing the target temperature, or stopping the supply of current to the heating element, or limiting the duty cycle of the pulses of electrical current supplied to the heating element.
2. The method according to claim 1, wherein the heating element is an electrically resistive heating element and the step of maintaining the temperature of the heating element at the target temperature comprises determining the electrical resistance of the heating element and adjusting the electrical current supplied to the heating element dependent on the determined electrical resistance.
3. The method according to claim 1, wherein the comparing the detected duty cycle with the expected duty cycle comprises periodically comparing the duty cycle with a first threshold duty cycle and using a hysteresis control loop to determine a trigger point at which to reduce the target temperature or limit the duty cycle of the pulses of electrical current.
4. The method according to claim 3, further comprising, if the duty cycle is less than a second threshold duty cycle while the temperature is above the target temperature, cutting the supply of electrical current to the heating element.
5. The method according to claim 4, further comprising limiting the duty cycle of the pulses of electrical current to a maximum duty cycle limit, wherein the first or second threshold, or both the first and second threshold, is proportional to the maximum duty cycle limit.
6. The method according to claim 5, wherein a variable A, where A is equal to the maximum duty cycle divided by the target temperature, is progressively reduced with increasing time following activation of the heating element.
7. A device for controlling an electrical heating element, comprising: a control circuit connected to the heating element, configured to maintain a temperature of the heating element at a target temperature by supplying pulses of electrical current to the heating element; and a detection circuit configured to monitor a duty cycle of the pulses of electrical current by determining a proportion of time that electrical current is supplied to the heating element, to provide a detected duty cycle and, to compare the detected duty cycle with an expected duty cycle, and if the detected duty cycle of the pulses of electrical current differs from the expected duty cycle or range of duty cycles, to instruct the control circuit to reduce the target temperature or stop the supply of current to the heating element, or limit the duty cycle or the pluses of electrical current.
8. The device according to claim 7, wherein the heating element is an electrically resistive heating element and the control circuit is configured to maintain the temperature of the heating element at the target temperature by determining the electrical resistance of the heating element and adjusting the electrical current supplied to the heating element dependent on the determined electrical resistance.
9. The device according to claim 7, wherein the detection circuit is configured to periodically compare the duty cycle with a first threshold duty cycle and comprises a hysteresis control loop configured to determine a trigger point at which to reduce the target temperature or limit the duty cycle of the pulses of electrical current.
10. The device according to claim 7, wherein the detection circuit is configured such that if the duty cycle is less than a second threshold duty cycle while the temperature is at or above the target temperature, the detection circuit instructs the control circuit to cut the supply of electrical current to the heating element.
11. The device according to claim 7, wherein the control circuit is configured to limit the duty cycle of the pulses of electrical current to a maximum duty cycle limit, such that a variable A, where A is equal to the maximum duty cycle divided by the target temperature, is progressively reduced with increasing time following activation of the heating element.
12. The device according to claim 7, wherein the control circuit is configured to cut the supply of electrical current to the heating element if the temperature of the heating element exceeds a temperature threshold.
13. The device according to claim 7, wherein the device is an aerosol generating device comprising a heating element, the aerosol generating device comprising an electrically heating smoking device.
14. The device according to claim 13, wherein the aerosol generating device is configured to receive an aerosol-forming substrate, and wherein the expected duty cycle or range of duty cycles is configurable dependent on a characteristic of the aerosol-forming substrate.
15. An aerosol generating system, comprising: an aerosol generating device comprising a heating element, and an aerosol generating article comprising an aerosol forming substrate, wherein the heating element is configured to heat the aerosol forming substrate to generate an aerosol, and wherein the aerosol generating device comprises: a control circuit connected to the heating element, configured to maintain a temperature of the heating element at a target temperature by supplying pulses of electrical current to the heating element; and a detection circuit configured to monitor a duty cycle of the pulses of electrical current by determining a proportion of time that electrical current is supplied to the heating element, to provide a detected duty cycle and, to compare the detected duty cycle with an expected duty cycle, and if the detected duty cycle of the pulses of electrical current differs from the expected duty cycle or range of duty cycles, to instruct the control circuit to reduce the target temperature or stop the supply of current to the heating element, or limit the duty cycle or the pulses of electrical current.
16. The system according to claim 15, wherein the aerosol generating device is configured so that the expected duty cycle or range of duty cycles is dependent on a characteristic of the aerosol-forming substrate.
17. A non-transitory computer readable storage medium having a computer program stored thereon, which, when run on programmable electric circuitry for an electrically operated aerosol generating device, causes the programmable electric circuitry to perform the method according to claim 1.
This application is a U.S. national phase application under 35 U.S.C. .sctn.371 of PCT/EP2013/068722, filed on Sep. 10, 2013, and claims the benefit of priority under 35 U.S.C. .sctn.119 from prior EP Application No. 12183837.9, filed on Sep. 11, 2012, the entire contents of each of which are incorporated herein by reference.
The present specification relates to an electrical heater and a method and device for controlling the heater to avoid spikes in temperature. The specification relates more particularly to an electrical heater configured to heat an aerosol-forming substrate and a method and device for avoiding undesirable combustion of the aerosol-forming substrate. The described device and method is particularly applicable to electrically heated smoking devices.
Electrically heated smoking devices are known, which operate at lower temperatures. By heating at lower temperature, the aerosol-forming substrate (which in case of a smoking device is tobacco based) is not combusted and far fewer undesirable compounds are generated.
It is desirable in such electrically heated smoking devices, and in other electrically heated aerosol generating devices, to ensure as far as possible that combustion of the substrate does not occur, even in extreme environmental conditions and under extreme usage patterns. It is therefore desirable to control the temperature of the heating element or elements in the device to reduce the risk of combustion while still heating to a sufficient temperature to ensure a desirable aerosol. It is also desirable to be able to detect or predict combustion of the substrate and control the heating element accordingly.
In one aspect of the present disclosure, there is provided a method of controlling an electrical heating element, comprising:
maintaining the temperature of the heating element at a target temperature by supplying pulses of electrical current to the heating element;
monitoring the duty cycle of the pulses of electrical current; and
determining if the duty cycle differs from an expected duty cycle or range of duty cycles, and if so, reducing the target temperature, or stopping the supply of current to the heating element or limiting the duty cycle of the pulses of electrical current supplied to the heating element.
The heating element may be part of an aerosol generating device, such as an electrically heating smoking device. The heating element may be configured to heat an aerosol-forming substrate continuously during operation of the device. An aerosol-forming substrate in this context is a substrate capable of releasing upon heating volatile compounds, which can form an aerosol. "Continuously" in this context means that heating is not dependent on air flow through the device. As the aerosol forming constituents of the aerosol-forming substrate become exhausted during heating, the power required to maintain a given target temperature falls. Depending on the evolution of the target temperature during operation of the heating element, the duty cycle may be limited to reduce the risk of combustion of the substrate occurring.
As the temperature is maintained at a known target temperature, any variation in the duty cycle or range of duty cycles expected to maintain the target temperature is indicative of abnormal conditions. For example, if the duty cycle remains much lower than expected while the temperature is maintained, it may be due to an external heat source, such as a combusting substrate. If the duty cycle remains higher than expected it may be due to abnormal cooling of the heating element as a result of excessive airflow past the heater, which in a smoking device means intense puffing by the user. Intense puffing can lead to a higher oxygen concentration that increases the chance of undesirable combustion of the aerosol-forming substrate.
The heating element may be an electrically resistive heating element and the step of maintaining the temperature of the heating element at the target temperature may comprise determining the electrical resistance of the heating element and adjusting the electrical current supplied to the heating element dependent on the determined electrical resistance. The step of maintaining the temperature of the heating element at the target temperature may comprise using a PID control loop. Alternatively, other mechanisms for maintaining the temperature may be used, such as a simple thermostat type on/off control mechanism that is less expensive than a PID control loop. Furthermore, mechanisms for temperature sensing other than detecting the electrical resistance of the heating element may be used, such as bimetallic strips, thermocouples or a dedicated thermistor or electrically resistive element that is electrically separate to the heating element. These alternative temperature sensing mechanisms may be used in addition to or instead of determining temperature by monitoring the electrical resistance of the heating element. For example, a separate temperature sensing mechanism may be used in a control mechanism for cutting power to the heating element when the temperature of the heating element exceeds a target temperature.
The step of determining if the duty cycle differs from an expected duty cycle may comprise periodically comparing the duty cycle with a first threshold duty cycle and using a hysteresis control loop to determine a trigger point at which to reduce the target temperature or limit the duty cycle of the pulses of electrical current. Using a hysteresis control loop ensures that very short term fluctuations in duty cycle do not trigger a reduction in temperature or applied power. Only after a sustained period of abnormal duty cycle behaviour is the trigger point reached.
The method may comprise, if the duty cycle is less than a second threshold duty cycle while the temperature is at or above the target temperature, cutting the supply of electrical current to the heating element. As described, a very low duty cycle with a sustained temperature is indicative of an external heat source and may be the result of combustion of a substrate adjacent to or surrounding the heating element. In this circumstance the power to the heating element may be cut to ensure that the user of the device does not receive any more undesirable compounds.
The method may comprise limiting the duty cycle of the pulses of electrical current to a maximum duty cycle limit. The maximum duty cycle limit may be varied on the basis of a pre-programmed control strategy. For example the maximum duty cycle may be reduced with increasing time, either stepwise or continuously, as the substrate dries out. The first or second threshold, or both the first and second threshold, may be proportional to the maximum duty cycle limit. For example, the first threshold may be maximum duty cycle limit. The second threshold may be a fixed proportion of the maximum duty cycle limit or may be a fixed duty cycle. Alternatively, both the first and second thresholds may be absolute limits.
In another aspect of the disclosure, there is provided a device for controlling an electrical heating element, comprising:
a control circuit connected to the heating element, configured to maintain the temperature of the heating element at a target temperature by supplying pulses of electrical current to the heating element; and
a detection circuit configured to monitor the duty cycle of the pulses of electrical current and if the duty cycle of the pulses of electrical current differs from an expected duty cycle or range of duty cycles, to instruct the control circuit to reduce the target temperature or stop the supply of current to the heating element or limit the duty cycle or the pulses of electrical current.
The heating element may be an electrically resistive heating element and the control circuit is configured to maintain the temperature of the heating element at the target temperature by determining the electrical resistance of the heating element and adjusting the electrical current supplied to the heating element dependent on the determined electrical resistance. The control circuit may comprise a PID control loop.
The detection circuit may be configured to periodically compare the duty cycle with a first threshold duty cycle and may comprise a hysteresis control loop configured to determine a trigger point at which to reduce the target temperature or limit the duty cycle of the pulses of electrical current.
The detection circuit may be configured such that if the duty cycle is less than a second threshold duty cycle while the temperature is at or above the target temperature, the detection circuit instructs the control circuit to cut the supply of electrical current to the heating element.
The target temperature may be constant or may alter with time.
The control circuit may be configured to limit the duty cycle of the pulses of electrical current to a maximum duty cycle limit, wherein for a given target temperature the maximum duty cycle limit is progressively reduced with increasing time following activation of the heating element. If the target temperature is configured to increase with time at any point following activation of the heating element, then the maximum duty cycle may also increase. In one embodiment the variable A, where A is equal to the maximum duty cycle divided by the target temperature, is progressively reduced with increasing time following activation of the heating element.
The control circuit may be configured to cut the supply of electrical current to the heating element if the temperature of the heating element exceeds a temperature threshold. For example, if the temperature of the heating element is detected to be 7.degree. C. or more above the target temperature the supply of power may be cut as the risk of combustion would otherwise be too high.
The device may be an aerosol generating device comprising a heating element, such as an electrically heating smoking device. The heating element may be configured to heat an aerosol-forming substrate continuously during operation of the device.
The aerosol generating device may be configured to receive an aerosol-forming substrate, and wherein the expected duty cycle or range of duty cycles is configurable dependent on a characteristic of the aerosol-forming substrate.
In a further aspect of the disclosure, there is provided an aerosol generating system, comprising:
an aerosol generating device comprising a heating element, and an aerosol generating article comprising an aerosol forming substrate, wherein the heater is configured to heat the aerosol forming substrate to generate an aerosol, and wherein the aerosol generating device comprises: a control circuit connected to the heating element, configured to maintain the temperature of the heating element at a target temperature by supplying pulses of electrical current to the heating element;
The aerosol generating device may be configured so that the expected duty cycle or range of duty cycles is dependent on a characteristic of the aerosol-forming substrate. The aerosol generating article may include means to allow the characteristic to be determined by the aerosol generating device, such as an electrically resistive component, optically detectable indicia or a characteristic shape or dimension. Different substrates may combust under different conditions and may contain different amounts of aerosol former or liquid, and so may be at risk of combustion at different temperatures and times.
In another aspect of the disclosure, there is provided a method of controlling an electrical heating element, comprising:
maintaining the temperature of the heating element at a target temperature during a plurality of heating phases by supplying electrical power to the heating element;
limiting the power supplied to the heating element during each heating phase to a threshold power level, such that a variable B, where B is equal to the threshold power level divided by the target temperature, is progressively reduced with increasing time following activation of the heating element.
The heating element may be part of an aerosol generating device, such as an electrically heating smoking device. The heating element may be configured to heat an aerosol-forming substrate continuously during operation of the device. "Continuously" in this context means that heating is not dependent on air flow through the device. As the aerosol forming constituents of the aerosol-forming substrate become exhausted during heating, the power required to maintain a given target temperature falls. The target temperature of the heating element may change during operation of the heating element and the duty cycle may be correspondingly limited to reduce the risk of combustion of the substrate occurring. If the target temperature is configured to increase with time at any point following activation of the heating element, then the maximum duty cycle may also increase.
The step of maintaining may comprise supplying power as pulses of electrical current, and the step of limiting the power supplied may comprise limiting the duty cycle of the pulses of electrical current to below a threshold duty cycle, the threshold duty cycle divided by the target temperature being progressively reduced for each successive heating phase following activation of the heating element.
Alternatively, or in addition, the step of limiting the power supplied may comprise limiting the voltage applied to the heating element to below a threshold voltage.
In a further aspect of the disclosure, there is provided a device for controlling an electrical heating element, comprising:
a control circuit coupled to a heating element, the control circuit configure to maintain the temperature of the heating element at a target temperature during a plurality of heating phases by supplying electrical power to the heating element, and to limit the power supplied to the heating element during each heating phase to a threshold power level, such that a variable B, where B is equal to the threshold power level divided by the target temperature, is progressively reduced with increasing time following activation of the heating element.
The control circuit may be configured to supply power as pulses of electrical current, and to limit the power supplied to the heating element by limiting the duty cycle of the pulses of electrical current to below a threshold duty cycle, the threshold duty cycle divided by the target temperature being progressively reduced for each successive heating phase following activation of the heating element.
The device may be an aerosol generating device comprising a heating element, such as an electrically heating smoking device.
The aerosol generating device may be configured to receive an aerosol-forming substrate, and the duration of the heating phases and the threshold duty cycle for each heating phase may be configurable dependent on a user input to the control circuit or dependent on a sensed characteristic of the aerosol-forming substrate or dependent on a sensed environmental parameter. So a particular substrate may require a different heating profile in order to give desirable results and different users may prefer different heating profiles.
an aerosol generating device comprising a heating element, and an aerosol generating article comprising an aerosol forming substrate, wherein the heater is configured to heat the aerosol forming substrate to generate an aerosol, and wherein the aerosol generating device comprises: a control circuit coupled to the heating element, the control circuit configure to maintain the temperature of the heating element at a target temperature during a plurality of heating phases by supplying electrical power to the heating element, and to limit the power supplied to the heating element during each heating phase to a threshold power level, such that a variable B, where B is equal to the threshold power level divided by the target temperature, is progressively reduced with increasing time following activation of the heating element.
The aerosol generating device may be configured so that the threshold power level is dependent on a characteristic of the aerosol-forming substrate. The aerosol generating article may include means to allow the characteristic to be determined by the aerosol generating device, such as an electrically resistive component, optically detectable indicia or a characteristic shape or dimension. Different substrates may combust under different conditions and may contain different amounts of aerosol former or liquid, and so may be at risk of combustion at different temperatures and times.
The control of the heating element as described in any of the preceding aspects of the disclosure may be implemented in a computer program which, when run on programmable electric circuitry for an electrically operated aerosol generating device, causes the programmable electric circuitry to perform the control method. The computer program may be provided on a computer readable storage medium.
In a still further aspect of the disclosure, there is provided an aerosol generating device comprising:
a detection circuit configured to detect a temperature of the heating element; and
a control circuit coupled to the heating element and the detection circuit, wherein the control circuit is configured to control the supply of power to the heating element from a power source, and wherein the control circuit is configured to prevent the supply of power to the heating element from the power source if the detection circuit detects that the temperature of the heating element is above a threshold temperature.
The threshold temperature may vary with time following activation of the heating element. The aerosol generating device may be an electrically heated smoking device.
In yet a further aspect of the disclosure, there is provided an aerosol generating system, comprising:
an aerosol generating device comprising a heating element, and an aerosol generating article comprising an aerosol forming substrate, wherein the heater is configured to heat the aerosol forming substrate to generate an aerosol, and wherein the aerosol generating device comprises: a detection circuit configured to detect a temperature of the heating element; and a control circuit coupled to the heating element and the detection circuit, wherein the control circuit is configured to control the supply of power to the heating element from a power source, and wherein the control circuit is configured to prevent the supply of power to the heating element from the power source if the detection circuit detects that the temperature of the heating element is above a threshold temperature.
In all of the aspects of the disclosure, the heating element may comprise an electrically resistive material. Suitable electrically resistive materials include but are not limited to: semiconductors such as doped ceramics, electrically "conductive" ceramics (such as, for example, molybdenum disilicide), carbon, graphite, metals, metal alloys and composite materials made of a ceramic material and a metallic material. Such composite materials may comprise doped or undoped ceramics. Examples of suitable doped ceramics include doped silicon carbides. Examples of suitable metals include titanium, zirconium, tantalum platinum, gold and silver. Examples of suitable metal alloys include stainless steel, nickel-, cobalt-, chromium-, aluminium-titanium-zirconium-, hafnium-, niobium-, molybdenum-, tantalum-, tungsten-, tin-, gallium-, manganese-, gold- and iron-containing alloys, and super-alloys based on nickel, iron, cobalt, stainless steel, Timetal.RTM. and iron-manganese-aluminium based alloys. In composite materials, the electrically resistive material may optionally be embedded in, encapsulated or coated with an insulating material or vice-versa, depending on the kinetics of energy transfer and the external physicochemical properties required.
As described, in any of the aspects of the disclosure, the heating element may be part of an aerosol generating device. The aerosol generating device may comprise an internal heating element or an external heating element, or both internal and external heating elements, where "internal" and "external" refer to the aerosol-forming substrate. An internal heating element may take any suitable form. For example, an internal heating element may take the form of a heating blade. Alternatively, the internal heater may take the form of a casing or substrate having different electro-conductive portions, or an electrically resistive metallic tube. Alternatively, the internal heating element may be one or more heating needles or rods that run through the centre of the aerosol-forming substrate. Other alternatives include a heating wire or filament, for example a Ni--Cr (Nickel-Chromium), platinum, tungsten or alloy wire or a heating plate. Optionally, the internal heating element may be deposited in or on a rigid carrier material. In one such embodiment, the electrically resistive heating element may be formed using a metal having a defined relationship between temperature and resistivity. In such an exemplary device, the metal may be formed as a track on a suitable insulating material, such as ceramic material, and then sandwiched in another insulating material, such as a glass. Heaters formed in this manner may be used to both heat and monitor the temperature of the heating elements during operation.
During operation, the aerosol-forming substrate may be completely contained within the aerosol-generating device. In that case, a user may puff on a mouthpiece of the aerosol-generating device. Alternatively, during operation a smoking article containing the aerosol-forming substrate may be partially contained within the aerosol-generating device. In that case, the user may puff directly on the smoking article.
The aerosol-generating device may further comprise a power supply for supplying power to the heating element. The power supply may be any suitable power supply, for example a DC voltage source. In one embodiment, the power supply is a Lithium-ion battery. Alternatively, the power supply may be a Nickel-metal hydride battery, a Nickel cadmium battery, or a Lithium based battery, for example a Lithium-Cobalt, a Lithium-Iron-Phosphate, Lithium Titanate or a Lithium-Polymer battery.
FIG. 1 is a schematic diagram of an aerosol generating device;
FIG. 2 is a schematic diagram of a temperature control circuit for a device of the type shown in FIG. 1;
FIG. 3 illustrates an evolution of a maximum duty cycle limit during a smoking session using a device of the type shown in FIG. 1;
FIG. 4 is a flow diagram illustrating one process for detecting abnormal duty cycle patterns;
FIG. 5 illustrates an example of a temperature reduction of the heating element following detection of excessive puffing by a user;
FIG. 6 is a flow diagram illustrating one process for detecting combustion of the substrate;
FIG. 7 illustrates an example of combustion detection using a process as illustrated in FIG. 6; and
FIG. 8 is a flow diagram illustrating a process for cutting power to the heating element following detection of undesirably high temperature.
In FIG. 1, the components of an embodiment of an electrically heated aerosol generating device 100 are shown in a simplified manner. Particularly, the elements of the electrically heated aerosol generating device 100 are not drawn to scale in FIG. 1. Elements that are not relevant for the understanding of this embodiment have been omitted to simplify FIG. 1.
The electrically heated aerosol generating device 100 comprises a housing 10 and an aerosol-forming substrate 12, for example a cigarette. The aerosol-forming substrate 12 is pushed inside the housing 10 to come into thermal proximity with the heating element 14. The aerosol-forming substrate 12 will release a range of volatile compounds at different temperatures. By controlling the maximum operation temperature of the electrically heated aerosol generating device 100 to be below the release temperature of some of the volatile compounds, the release or formation of these smoke constituents can be avoided.
FIG. 2 illustrates control circuitry used to provide the described temperature regulation in accordance with one embodiment of the invention.
The heater 14 is connected to the battery through connection 22. The battery 16 provides a voltage V2. In series with the heating element 14, an additional resistor 24, with known resistance r, is inserted and connected to voltage V1, intermediate between ground and voltage V2. The frequency modulation of the current is controlled by the microcontroller 18 and delivered via its analog output 30 to the transistor 26 which acts as a simple switch.
The regulation is based on a PID regulator that is part of the software integrated in the microcontroller 18. The temperature (or an indication of the temperature) of the heating element is determined by measuring the electrical resistance of the heating element. The temperature is used to adjust the duty cycle, in this case the frequency modulation, of the pulses of current supplied to the heating element in order to maintain the heating element at a target temperature. The temperature is determined at a frequency chosen to match the control of the duty cycle, and may be determined as often as once every 100 ms.
The analog input 28 on the microcontroller 18 is used to collect the voltage across the resistance 24 and provides the image of the electrical current flowing in the heating element. The battery voltage V+ and the voltage across resistor 24 are used to calculate the heating element resistance variation and or its temperature.
The heater resistance to be measured at a particular temperature is R.sub.heater. In order for microprocessor 18 to measure the resistance R.sub.heater of the heater 14, the current through the heater 14 and the voltage across the heater 14 can both be determined. Then, the following well-known formula can be used to determine the resistance: V=IR (1)
In FIG. 2, the voltage across the heater is V2-V1 and the current through the heater is l. Thus:
The additional resistor 24, whose resistance r is known, is used to determine the current I, again using (1) above. The current through the resistor 24 is I and the voltage across the resistor 24 is V1. Thus:
Thus, the microprocessor 18 can measure V2 and V1, as the aerosol generating system is being used and, knowing the value of r, can determine the heater's resistance at a particular temperature, R.sub.heater.
The heater resistance is correlated to temperature. A linear approximation can be used to relate the temperature T to the measured resistance R.sub.heater at temperature T according to the following formula:
##EQU00004## where A is the thermal resistivity coefficient of the heating element material and R.sub.0 is the resistance of the heating element at room temperature T.sub.0.
An advantage of these embodiments is that no temperature sensor, which can be bulky and expensive, is required. Also the resistance value can be used directly by the PID regulator instead of temperature. If the resistance value is held within a desired range, so too will the temperature of the heating element. Accordingly the actual temperature of the heating element need not be calculated. However, it is possible to use a separate temperature sensor and connect that to the microcontroller to provide the necessary temperature information.
The microcontroller may be programmed to limit the maximum allowed duty cycle. The maximum allowed duty cycle may change with time following activation of the heating element. FIG. 3 illustrates the progress a smoking session using a device of the type shown in FIG. 1. The target temperature of the heating element is indicated by line 30, and as can be seen is maintained at 375.degree. C. through the smoking session, which lasts for six minutes in total. The smoking session is split into phases by the microcontroller, with different maximum duty cycle limits in different phases. Duty cycle in this context means the percentage of time that the power is being supplied, with switch 26 closed. In the example illustrate in FIG. 3, in a first phase the duty cycle is limited to 95% for 30 seconds. During this period the heating element is being raised to the target temperature. In a second phase, again of 30 seconds, the duty cycle is limited to 65%. Less power is required to maintain the temperature of the heating element than is required to heat it up. In a third phase of 30 seconds the duty cycle is limited to 60%. In a fourth phase of 90 seconds the duty cycle is limited to 55%, in a fifth phase of 60 seconds the duty cycle is limited 50%, and in a sixth phase of 120 seconds the duty cycle is limited to 45%.
As the substrate is depleted less heat is removed by vaporisation so less power is required to maintain the temperature of the heating element at the target temperature. Furthermore, the temperature of the surrounding parts of the device increases with time and so absorb less energy with time. Accordingly, to reduce the chance of combustion, the maximum permitted power is reduced with time for a given target temperature. As a general rule, the maximum permitted power or maximum duty cycle, divided by the target temperature, is reduced progressively with time following activationof the heating element during a single smoking session.
Excessive puffing behaviour may also be determined. Each time a user takes a puff on the device, drawing air past the heating element, the amount of oxygen in contact with the substrate is increased, increasing the chance of combustion at a given temperature. With each puff heating element is cooled. The temperature control loop will compensate for this cooling by raising the duty cycle of the current pulses temporarily. Extended periods at or near to the duty cycle limit may be indicative of excessive puffing and trigger a reduction in the duty cycle limit.
By limiting the maximum duty cycle to a level which would be expected within the bounds of "normal" user behaviour and environmental conditions, temperature spikes may be avoided. Clearly, the duty cycle limit and the way in which it changes over time can be experimentally determined to suit particular device designs, substrates and usage scenarios.
The duty cycle of the current pulses can be monitored by the microcontroller, and if the duty cycle differs from an expected duty cycle over a sustained period, the microcontroller can take corrective action or can terminate the supply of power to the heating element.
The maximum duty cycle limit may be set to be an upper limit of an expected duty cycle level for normal user behaviour or set to suit a particular user in accordance with his or her preference. If the actual duty cycle is then at the maximum duty cycle limit for much of the time it is indicative that the system is being cooled more than expected by excessive user puffing. As described above, with excessive puffing there is an increased risk of combustion owing to increased oxygen in contact with the substrate. FIG. 4 illustrates a hysteresis control loop, using a Schmitt trigger debounce approach, for detecting such abnormal puffing behaviour and reducing the target temperature or duty cycle limit when such abnormal puffing is detected. However, it should be clear that there are alternatives to a Schmitt trigger control loop, such as a sliding window control, Infinite Impulse Response (IIR) filters and Finite Impulse Response (FIR) filters.
The process of FIG. 4 starts and proceeds to step 400, in which an arbitrary state variable "state", which is initially set as 0 is modified by a factor f, which is less than one, say example 0.75. In step 410 the duty cycle is compared with a duty cycle threshold value DC.sub.1. If the duty cycle is greater than or equal to the duty cycle threshold value then the state variable is increased by amount c, say 0.25, in step 420 before passing to step 430. The duty cycle threshold value DC.sub.1 may be the maximum duty cycle limit of some proportion of the maximum duty cycle limit. If the duty cycle is less that the threshold duty cycle the state variable is unchanged and the process moves to step 430. The state variable is then compared with a state threshold ST in step 430. The state threshold may be step as 0.8 for example. If the state variable is less than or equal to the state threshold then the process returns to step 400. If the state variable is greater than the state threshold then a pre-burning condition is detected and the either target temperature of the heating element or the maximum duty cycle limit is reduced in step 440. The state variable is then reset in step 450 before the process returns to step 400.
The process of FIG. 4 ensures that very short term fluctuations do not trigger a pre-burning condition detection. Only if the duty cycle exceeds the threshold duty cycle for several cycles of the control process will the pre-burning condition be detected. The control loop of FIG. 4 is repeated periodically, for example every 100 ms, corresponding to the frequency of the PID regulator control loop.
FIG. 5 illustrates a reduction in the target temperature resulting from a control process as illustrated in FIG. 4. The upper line 50 indicates the temperature of the heating element. The lower line 55 is the duty cycle of the current signal. FIG. 5 shows that at around 275 seconds after the start of the smoking session, the pre-burning detection mechanism triggered because, starting at around 240 seconds, a lower duty cycle limit caused the temperature to drop more during puffs and the system compensated by keeping the duty cycle at its upper limit for a longer time. The target temperature was then reduced to 350.degree. C.
FIG. 6 illustrates a hysteresis control loop, again using a Schmitt trigger debounce approach, for detecting combustion of the substrate. In step 600 an arbitrary state variable "state", which is initially set as 0, is modified by a factor f, which is less than one, say example 0.9. In step 610, the duty cycle is compared to a second duty cycle threshold DC.sub.2. The second duty cycle threshold is set at 75% of the maximum duty cycle threshold. If the duty cycle is less that the second duty cycle threshold the state variable is incremented by b, in this example 0.3, in step 620, before proceeding to step 630. If the duty cycle is greater than or equal to the second duty cycle threshold, then the state variable is unchanged and the process proceeds directly to step 630. In step 630 the state variable is compared with a state variable threshold ST, which is equal to one in this example. If the state variable is greater than ST then the power supply is cut to the heating element. The microprocessor simply holds switch 26 open. The process then ends. If the state variable is less than or equal to ST the process returns to step 600.
FIG. 7 illustrates a burning detection using a process of the type shown in FIG. 6. FIG. 7 shows a significant drop in duty cycle at around 140 seconds, but this was not sufficient to trigger the burning detection mechanism. However, at around 155 seconds, the duty cycle dropped below the burning detection filter minimum limit and stayed low for some time while the temperature remained at or above a predetermined target. The comparison of actual temperature with the predetermined target may incorporated into the control loop of FIG. 6 or may be implemented as a separate process. This triggered the immediate stop of power to the heating element. In effect, the burning detection mechanism detected energy starting to come from the substrate rather than from its electrical source and stopped the smoking experience before the substrate entered auto-combustion.
In addition to the pre-burning and burning detection processes described with reference to FIGS. 4 and 6, power to the heating element may be cut on the basis of detected temperature alone. FIG. 8 illustrates an example of a control loop for cutting power based on detection of excessive temperature. The control loop of FIG. 8 may be incorporated into the control loop of FIG. 4 or FIG. 6. For example, in the process of FIG. 4, step 800 of FIG. 8 may be performed immediately prior to step 400 in each loop. Alternatively, the control loop of FIG. 8 may be implemented as a separate control loop. In step 800 the actual detected temperature T.sub.actual (as determined by the resistance of the heating element or by a separate temperature sensor) is compared with the target temperature T.sub.target. If the actual temperature is less than the target temperature the process is repeated or, if incorporated into another control process, the remaining step of the control process are performed. If the actual temperature is at or exceeds the target temperature the process proceeds to step 810, in which power to the heating element is cut. Power to the heating element may be cut by the microcontroller controlling a switch, such as switch 26 in FIG. 2. The device may then be prevented from operating for a predetermined period of time, during which the heating element cools to an acceptable temperature. The use of a simple temperature threshold for cutting power to the heating element provides a direct way to prevent or reduce the likelihood of combustion of the substrate.
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