EP1809424A1

EP1809424A1 - Nebuliser comprising means for pressurizing a liquid for nebulisation

Info

Publication number: EP1809424A1
Application number: EP05812311A
Authority: EP
Inventors: Jean-Pierre Le Pesant; Hugues Brouard
Original assignee: Osmooze SA
Current assignee: Osmooze SA
Priority date: 2004-10-29
Filing date: 2005-10-20
Publication date: 2007-07-25
Also published as: JP2008517756A; CA2585329A1; US7766253B2; CN100522387C; WO2006048523A1; RU2381075C2; BRPI0517267A; RU2007119710A; US20070262163A1; AU2005300471A2; FR2877241B1; CN101065192A; FR2877241A1; AU2005300471A1

Abstract

The invention relates to a device (30) for nebulising a liquid, comprising a nebulisation head (40) with a capillary tube (40-1) and an ejection nozzle (40-2) for the ejection of a liquid (43), a reservoir (42) for the supply of liquid (43) to the nebulisation head, a vibrating means (44) for vibrating the nebulisation head, in order to eject liquid droplets into a nebulisation jet. According to the invention, the device (30) comprises means for application of a pressure greater than a first threshold pressure, above which the liquid flows through the nebulisation head when not in vibration, and below a second threshold pressure above which the liquid flows through the nebulisation head when in vibration, to the liquid at the entrance to the nebulisation head (40), during nebulisation cycles. The above has the advantage of increasing nebulisation flow and low sensibility to changes in attitude and vibrations.

Description

NEBULATOR COMPRISING MEANS FOR PRESSURIZING A NEBULIZING LIQUID

The present invention relates to a device for nebulizing a liquid, comprising a nebulizing head comprising a capillary tube and a nozzle for ejecting a liquid, a reservoir for supplying liquid to the nebulization head, connected to the head method of nebulizing a pipe, vibrating means for driving the vibration nebulizing head to eject liquid droplets in a nebulizing jet, and excitation means for applying to the vibrating means an excitation signal.

A nebulizing device of the aforementioned type is described in the international application WO 99/46126 (US 6,460,980) in connection with the production of an inkjet printing head. Such a device is, however, capable of various other applications, including applications to the nebulization of liquids in the air, for humidification or air cooling purposes, or to distribute sanitizers, deodorants, disinfectants, perfumes, ... as described for example in the application EP 0714709 or the application WO 00/78467. The present invention relates in particular to such applications.

Figure 1 shows schematically the conventional structure of such a device. The device 10 comprises a nebulizing head 20, an intermediate reservoir 21 containing a liquid 22 to be sprayed, a main reservoir 24 also containing liquid 22, a pipe 25 connecting the reservoir 21 to the nebulizing head 20 and a pipe 26 equipped with 'a electric pump 27, connecting the reservoir 21 to the tank 24. The nebulizing head 20, substantially horizontal, comprises a capillary tube 20-1 and a nozzle 20-2 ejection of the liquid. It is generally in the form of a hollow needle with an internal diameter less than a millimeter and a length of a few centimeters, the body of which forms the capillary tube 20-1 and whose distal end, beveled, forms the nozzle. ejection 20-2. The nebulizing head 20 is mechanically coupled to a vibrating means, generally a piezoelectric transducer 28 with a resonator, which is electrically powered by an alternating signal Sv supplied by an excitation circuit EXCT. The EXCT excitation circuit is controlled by a CNTCT control circuit which defines nebulization cycles whose duration is a function of the intended application.

Under normal operating conditions, the liquid level in the intermediate reservoir 21 is at a height H1 of the longitudinal axis of the nebulizing head 20. The reservoir 21 being subjected to the atmospheric pressure Patm, the liquid 22 present in the the duct 25, at the inlet of the nebulizing head 20, is subjected to atmospheric pressure, to which is added an overpressure PhI equal to the hydrostatic pressure imposed by the liquid column of height H1, with PhI = p * g * Hl, p being the density of the liquid and gravity.

When the excitation signal Sv is applied to the transducer 28, the nebulization head comes into resonance and a vibration belly appears at its end 20-2. Droplets 22-2 of liquid 22 are ejected in a direction substantially perpendicular to the plane of the beveled section of the nebulizing head, forming a kind of mist of droplets or "spray jet". During the nebulization, the nebulizing head 20 is supplied with liquid by capillarity and by gravity (effect of the hydrostatic overpressure). Air circulation means such as a fan (not shown) may be provided to increase the range of the nebulizer jet.

At rest, when the nebulizing head is not driven in vibration, the liquid 22 is retained in the misting head by capillarity, and the hydrostatic pressure is compensated by the appearance of a convex meniscus 22-1 of liquid 22 at the end of the nebulizing head, due to the surface tension forces acting on the liquid. Beyond a critical pressure threshold ShI, the meniscus 22-1 breaks and the liquid 22 flows through the nebulizing head. It follows from the foregoing that the level of the liquid in the intermediate tank 21 must be precisely controlled, so that the hydrostatic pressure is kept below the threshold ShI, which is generally very low and of the order of 50 to 150 Pa.

Thus, the optimum height Hl depends on the threshold ShI and the physicochemical characteristics of the liquid, in particular the viscosity, the density, the surface tension forces, as well as the inside diameter of the capillary tube of the nebulization head. This height is generally low, of the order of 5 to 15 mm with aqueous or alcoholic solutions and a fogging head whose capillary tube has an internal diameter of the order of 0.6 mm. The height H1 is kept substantially constant by the CNTCT circuit, which monitors the liquid level by means of a level detector 23 arranged in the tank 21, and activates the pump 27 punctually.

According to a known improvement shown in FIG. 2, making it possible not to use a pump, the device comprises an intermediate reservoir 21 'connected to a main tank 24' by a pipe 26 'according to the principle of communicating vessels. The tank 21 'is subjected to the atmospheric pressure Patm while the tank 24' is hermetically closed and is subjected to a pressure P1 lower than the atmospheric pressure, which prevents the tank 24 'from emptying completely into the tank 21'. At the hydrostatic equilibrium, the level of the liquid 22 in the tank 24 'is above that of the liquid in the tank 21'. When the liquid level in the tank 21 'becomes lower than the high level of the pipe 26', air passes into the tank 24 'and liquid is transferred into the tank 21'. An auxiliary pipe 27 'may also be provided to introduce air into the upper part of the tank 24'. Thus, the height of liquid in the tank 21 'is regulated automatically.

Despite this improvement, the nebulization device that has just been described still has various disadvantages.

The device is particularly sensitive to changes in attitude that move the liquid in the intermediate reservoir, as well as other phenomena producing similar effects, for example vibrations transmitted by the external environment. Such changes of attitude or vibrations can lead to the flow of drops at the end of the nebulizing head. Indeed, the height Hl being low, the movements of the liquid surface in the intermediate tank may cause an exceeding of the critical threshold ShI which breaks the meniscus 22-1 at the end of the nebulizing head.

Now, the present invention aims at applications where such changes of attitude and vibrations are frequent, such as the realization of nebulizers embedded in vehicles (trains, coaches, cars ...) or the realization of portable foggers. Thus, a first object of the invention is to provide a nebulizing device which is insensitive to changes of attitude and other phenomena acting on the liquid level in the tank.

Another disadvantage of the conventional nebulization device is that its nebulization rate depends on the nature of the liquid that is nebulized. There are thus different flow rates in a ratio ranging from 2 to 10 between liquids in aqueous solution and liquids in alcoholic solution, for the same nebulization head. For example, a fogging head with an internal diameter of 0.6 mm and a length of 27 mm, driven in vibration at 20OkHz, allows to obtain flow rates of the order of 1 to 3 grams per minute with liquids formed mainly of water (in which air treatment products are dissolved), but in the range of 0.1 to 0.6 grams per minute only with water-based solutions , ethyl alcohol and dipropylene glycol.

Thus, another objective of the present invention is to significantly increase the nebulization rate of certain solutions, especially alcoholic solutions.

More generally, an object of the invention is to control the flow of nebulization so that it can increase or decrease it without changing the nebulizing head.

At least one objective of the present invention is achieved by the provision of a misting device of the type described above, comprising means for applying to the liquid at the inlet of the head of the nebulization, during nebulization cycles, a pressure greater than a first pressure threshold above which the liquid flows through the nebulizing head when it is not driven in vibration, and below a second pressure threshold beyond which the liquid flows through the nebulizing head when it is driven in vibration. According to one embodiment, an overpressure of the order of 1000 Pa at 3000 Pa is applied to the liquid at the inlet of the nebulization head, relative to the atmospheric pressure.

According to one embodiment, the means for applying a pressure greater than the first threshold and lower than the second threshold comprise a liquid column of height equal to the sum of a height of liquid in the tank and a height between the bottom of the tank. tank and nebulizing head.

According to one embodiment, the shape of the reservoir is such that the maximum height of the liquid in the reservoir is less than one-fifth of the height between the bottom of the reservoir and the nebulizing head.

According to one embodiment, the means for applying a pressure greater than the first threshold and lower than the second threshold comprise means for pressurizing the liquid present in the liquid supply tank of the nebulization head.

The liquid supply tank of the nebulizing head is for example a deformable bag which is subjected to crushing. According to one embodiment, the device comprises a flow or pressure limiter arranged in the pipe between the reservoir and the nebulization head.

According to one embodiment, the means for applying a pressure greater than the first threshold and lower than the second threshold comprise a valve arranged in the pipeline between the reservoir and the nebulizing head, and valve control means for closing the valve when the nebulizing head is not driven in vibration, and opening the valve when the nebulizing head is driven in vibration.

According to one embodiment, the flow or pressure limiter is integrated in the valve.

According to one embodiment, the device comprises means for controlling the excitation means, to define nebulization cycles interspersed with pauses during which the excitation signal is not applied to the vibrating means, in which the control means are arranged to chop a nebulization cycle into a plurality of microspheres separated by micropauses during which the excitation signal is not applied to the vibrating means.

According to one embodiment, the control means of the excitation means are arranged to define nebulization cycles of a duration of the order of a hundred milliseconds to a few seconds, including nebulization microcycles of a duration of the order of the millisecond to a few tens of milliseconds.

According to one embodiment, the control means of the excitation means are arranged to interrupt the nebulization cycles during pauses longer than the duration of the nebulization cycles.

According to one embodiment, the control means of the valve do not close the valve during micropauses.

According to one embodiment, the control means of the valve are arranged to close the valve before the end of a nebulization cycle, so that the nebulizing head is empty of all or part of the liquid it contains before stopping to vibrate.

According to one embodiment, the device comprises means for switching to an active standby mode comprising nebulization microcycles separated by pauses of a duration at least 1000 times longer than the duration of the microcycles, in order to wet the head of the microcycle cyclically. nebulization. According to one embodiment, the device comprises a main reservoir arranged below the liquid supply tank of the nebulization head, and means for transferring liquid from the main reservoir to the liquid supply tank of the head of the nozzle. nebulization.

According to one embodiment, the device is applied to the nebulization of a liquid in the air, for the purpose of humidifying or cooling the air, or for diffusing a sanitizing, deodorizing or disinfecting product, or a perfume , or a combination of these products.

According to one embodiment, the device comprises a ventilation means for dispersing the nebulization jet. These and other objects, features and advantages of the present invention will be set forth in more detail in the following description of various aspects of the invention and of a nebulizing device according to the invention, given as a non-limiting example in relation to with the attached figures among which: FIG. 1 previously described schematically represents a conventional nebulization device; FIG. 2 previously described illustrates a known variant embodiment of the device of FIG. 1, FIG. 3 schematically represents a nebulization device according to the invention,

FIGS. 3A, 3B show electrical signals involved in the control of nebulization cycles according to the prior art, FIGS. 4A, 4B, 4C represent electrical signals involved in the control of nebulization cycles according to the invention,

FIG. 5 schematically represents the structure of control and excitation circuits represented in the form of blocks in FIG. 3, and

- Figures 6A, 6B are similar to Figures 4A, 4B and Figure 6C shows an electrical signal involved in the control of nebulization cycles according to the invention.

First aspect of the invention

A first aspect of the present invention is based on the finding that, when a nebulizing head of the type described above is in operation, that is to say driven in vibration, the liquid applied to the inlet of the head Nebulization may be subjected to a pressure well above the threshold ShI considered in the prior art as a limit not to exceed to prevent the liquid from flowing when the spray head is at rest. On the contrary, an increase in the overpressure in the nebulizing head advantageously increases the flow of nebulized liquid by facilitating the delivery of the liquid in the capillary tube, which is then in "forced pipe", provided not to exceed a second pressure threshold Sh2 beyond which the liquid begins to flow from the nebulizing head. However, the second pressure threshold Sh2 beyond which the liquid flows while the nebulization head is driven in vibration, is significantly higher than the first pressure threshold Shi. Experiments show that the threshold Sh.2 is generally of the order of 1000 to 3000 Pa (approximately 1 to 3% of the atmospheric pressure), and is a function of the dimensions of the nebulization head and the characteristics of the liquid to be sprayed. , while the first threshold is generally of the order of approximately 50 to 150 Pa, ie approximately 0.05 to 0.15% of the atmospheric pressure.

Thus, according to the invention: 1) defines a first pressure threshold ShI not to be exceeded when the nebulization head is at rest,

2) defining a second excess pressure threshold Sh2 not to be exceeded when the nebulizing head is driven in vibration,

3) when the fogging head is driven in vibration, the liquid in the fogging head is subjected to an overpressure higher than the threshold ShI but lower than the threshold Sh2, and 4) when the fogging head is at rest, the liquid in the fogging head Nebulizing head is subjected to a zero overpressure or at least lower than the threshold ShI.

This first aspect of the invention can be implemented in various ways. For example, the liquid reservoir which feeds the nebulizing head is put under overpressure by means of a gas cartridge or a compact compressor when the nebulizing head is driven in vibration, then is depressurized when the nebulizing head is resting. The overpressure of the reservoir can also be achieved by heating the air or gas above the liquid, or even by heating the entire reservoir to heat the air or the gas above the liquid, or by heating only a part of the liquid. The overpressure of the liquid reservoir can also be provided by a mechanical system moved by a spring, which imposes the liquid the desired pressure.

According to a first preferred embodiment, the liquid supply tank is a deformable bag which is crushed by a specific surface plate, subjected to a bearing force exerted by a spring or any other means.

On the other hand, instead of depressurizing the liquid reservoir when the nebulizing head is at rest, a valve can be arranged in the pipe connecting the reservoir and the nebulization head. In this case, the overpressure can be maintained permanently in the tank, provided to close the valve when the fogging head is at rest.

FIG. 3 diagrammatically represents a nebulizing device 30 according to a second preferred embodiment, in which the overpressure Sh 2 is a hydrostatic pressure imposed by a liquid column of height H2 that is greater than the conventional height H 1 described in the preamble.

The device 30 comprises a conventional nebulizing head 40, for example a hollow needle whose body 40-1 forms a capillary tube and whose distal end 40-2 is tapered to form an ejection nozzle. The nebulizing head 40 is connected via a pipe 41 to a single tank 42 which contains a liquid 43 to be sprayed. The reservoir 42 is subjected to the atmospheric pressure Patm and here forms both the main reservoir of the device and the feed tank of the nebulizing head. The nebulizing head is mechanically coupled to a vibrating means such as a piezoelectric transducer 44 with a resonator, excited by a signal Sv, for example a signal oscillating at 200 kHz. The signal The excitation circuit Sv is provided by an excitation circuit EXCT which is controlled by a control circuit CNTCT.

According to the invention, the reservoir 42 is arranged so that the surface of the liquid 43 in the reservoir is at a height H2 of the longitudinal axis of the nebulizing head, and the height H2 is chosen so that the liquid in the the pipe 41, at the inlet of the nebulizing head, is subjected, relative to the atmospheric pressure Patm, to an overpressure Ph2 equal to p * g * H2 such that:

ShI <Ph2 <Sh2

at a pressure Pr2 such that:

Patm + ShI <Pr2 <Patm + Sh2

ShI and Sh2 being the first and second overpressure thresholds described above, Patm + Shl a first pressure threshold corresponding to the first pressure threshold ShI, Patm + Sh2 a second pressure threshold corresponding to the second pressure threshold Sh2, Pr2 la liquid pressure at the inlet of the nebulizing head and Ph2 the applied pressure relative to the atmospheric pressure (or, in general, the pressure applied relative to the pressure at the outlet of the nebulization head, which is here atmospheric pressure).

According to the invention, a solenoid valve 45 is arranged in the pipe 41, between a first pipe section 41-1 connecting the inlet of the solenoid valve 45 to the tank 42 and a second pipe section 41-2 connecting the outlet of the The solenoid valve 45 at the inlet of the nebulizing head 40. The solenoid valve 40 is of the "normally closed" type and is driven by an opening and closing signal Sg supplied by the control circuit CNTCT. The solenoid valve is closed (fogging head isolated from the tank) when the fogging head is at rest and is opened by the CNTCT circuit when the fogging head is driven in vibration, subject to what will be described later in connection with a mode of excitation of the transducer 44 including pauses of very short duration during which the solenoid valve is left open.

At rest, the excess pressure of the liquid at the inlet of the nebulizing head 40 is zero and the solenoid valve prevents the flow of the liquid contained in the reservoir, the device is off or in a standby mode active described below.

When the nebulizing head 40 is driven in vibration, the pressure Ph.sub.2 applied to the liquid at the inlet of the nebulizing head makes it possible to appreciably increase the nebulization flow rate for various liquids, for example aqueous or alcoholic solutions, relative to operation based only on the capillarity and a hydrostatic overpressure lower than the threshold ShI.

As another advantage, the overpressure Ph2 makes it possible to increase the exit velocity of the droplets, ie the kinetic energy of the nebulization jet, which has the effect of increasing the length and therefore the range of the nebulization jet. It is thus possible to obtain a nebulization jet of length 5 to 30 cm or more. In some applications, this may make it possible not to use a flow of air (provided for example by a fan) to carry and disperse the nebulizing jet.

Depending on the importance of the Ph2 overpressure, the viscosity of the liquid and the characteristics of the head of nebulization, a flow limiter or a pressure limiter 46, shown schematically in dotted lines in FIG. 3, can be arranged between the solenoid valve 45 and the inlet of the nebulizing head 40.

In one embodiment, the flow or pressure limiter is integrated with the solenoid valve to form a solenoid-limiter block produced by means of micromechanical techniques. It may be a capillary effect flow limiter which is adjustable or parameterizable, for example a capillary tube having an adjustable internal diameter, or a dynamically controlled flow regulator in which the flow of the liquid causes a loss of load that limits the flow. It may also be a pressure regulator, for example a needle and spring regulator, which maintains the overpressure at the entrance of the nebulization head below the threshold SH2. Such a flow or pressure limiter makes it possible to adjust the flow rate in the pipe to a value corresponding to the nebulization capacity of the nebulization head, and makes it possible to provide a pipe of a diameter between the reservoir and the nebulizing head. internal which is not very low and an opening surface of the solenoid valve which is also not very low (and which would be too large in the absence of flow limiter or pressure). Another advantage is that the pressure is exerted quickly on the liquid present in the nebulizing head, as soon as the solenoid valve is opened, without the flow rate exceeding the limit allowed by the nebulizing head.

The pressurization of the liquid and the adjustment of the flow rate must be adapted to the nebulization capacity of the nebulizing head 40. are filled, the flow of nebulization obtained can be

10 to 20 times higher than the flow obtained with a conventional liquid supply. For example, with a spray head of 0.6 mm internal diameter, driven in vibration at 200 kHz, and a pressure of 1200 Pa (about 1.2% of the atmospheric pressure), the flow of nebulization can reach 50 mg / s instead of 0.5 mg / s by simple capillarity. The nebulized drops have a diameter of the order of 10 to 50 micrometers, or even more, under certain higher flow conditions described below.

Another advantage of the invention is to allow the realization of a nebulizer tolerant to the movements of the liquid in the tank (tilt or vibration of the tank) both when stopped in operation. Indeed,

It can be seen in FIG. 3 that the height of liquid H2 is equal to the sum of the height h1 between the bottom of the reservoir 42 and the longitudinal axis of the nebulizing head 40, and the height h 2 of liquid in the reservoir 42. However, obtaining an overpressure between the thresholds ShI and Sh2, for example an overpressure of the order of 1000 Pa to 3000 Pa, implies a height H2 of the order of 100 to 300 mm with aqueous or alcoholic solutions. Under these conditions, the shape of the tank can be chosen wider than it is high so that the variations in the height h.2 due to the movements of the liquid and the progressive consumption thereof are negligible in view of the height hl and, in all In fact, such variations do not lead to the overpressure Ph2 exceeding the threshold Sh2. In practice, the height h2 will preferably be less than 1/5 of the height h1.

It will be noted here that another advantage that results from the provision of a flow or pressure limiter is to be able to increase to an even higher value by example of 3000 Pa at 5000 Pa, the overpressure at the inlet of the pipe, upstream of the flow or pressure limiter, without exceeding the overpressure threshold Sh.2 at the inlet of the nebulizing head, so that the variations of overpressure, due for example to variations in the height h.2 when the liquid moves in the tank, or to the expansion of the liquid in the tank when it is subjected to a heating, are even more negligible in the face of the overpressure exerted on the liquid.

In one embodiment, the reservoir 42 is maintained by a height-adjustable fastening system, for example a rack system, allowing the user to adjust the height H2 as a function of the liquid used (the densities may be different from one liquid to another) referring to height adjustment charts h1 provided by the manufacturer. The height adjustment h1 can also be controlled by microprocessor by providing an electrically controlled rack, in order to be able to program a determined flow rate according to the intended application. In this case, height / flow charts for each type of liquid are recorded in the microprocessor program memory. In one embodiment, the tank is equipped with a level detector having a detection threshold that can be adjusted mechanically or electronically. Finally, the invention also allows a simplification of the nebulizer structure, since it is no longer imperative to provide an intermediate reservoir for the supply of the nebulizing head. Those skilled in the art will note, however, that the invention does not preclude the provision of an intermediate reservoir, in particular to allow the use of spare fluid cartridges, forming separate main tanks of the feed tank. liquid of the nebulizing head, for reasons of rationalization of the structure of the device, or to place these reservoirs outside the actual structure of the device. Thus, in one embodiment, an external reservoir is arranged below the reservoir that supplies the nebulizing head and the latter is recharged with liquid by means of a pump or any other means for transferring the liquid (for example by putting the external tank under pressure). Second aspect of the invention

In applications consisting of the nebulization of sanitizers, deodorants, disinfectants, or perfumes, short-term nebulization cycles separated by long-term breaks are generally defined. The duration of nebulization cycles is usually from a hundred milliseconds to a few hundred milliseconds, and rarely more than a few seconds. The duration of the breaks is generally much longer than the duration of the cycles, often several tens of seconds to several tens of minutes.

For this purpose, the control circuit of a conventional fogger defines a template signal Se, shown in FIG. 3A, which is for example at 1 when the fogging head must be driven in vibration, for a time t1 representing the duration a nebulization cycle, and which is 0 when the nebulization head must be at rest, for a time t2 representing the duration of a pause. In the prior art still, and as illustrated in FIG. 3B, the excitation signal Sv is applied to the transducer 44 during the entire duration t1 of the nebulization cycle, which therefore consists of a "continuous nebulization cycle".

The invention is based here on the observation that the prediction of very short periods of nebulization duration separated by periods of rest also of very short duration, can significantly increase the average flow rate of nebulized liquid, including the average flow of nebulization of alcoholic solutions used for the diffusion of active ingredients, especially various scents and fragrances . Thus, according to the invention, a nebulization cycle is chopped into a plurality of periods of nebulization of very short duration, by applying to the transducer 44 pulse trains of the excitation signal Sa. For the sake of simplification of the language, the periods of nebulization of very short duration will be called "microcycles" of nebulization (or microcycles of excitation of the transducer) and the periods of rest of very short corresponding duration will be designated "micropauses".

In order to control the duration of the nebulization cycles and microcycles, the CNTCT and EXCT circuits of the device 30 according to the invention (FIG 3) use a template signal Se shown in FIG 4A, and a sub-mask signal Sse represented in Figure 4B. The signal Se is at 1 during the duration t3 of a nebulization cycle and is at 0 during the time t4 of a pause. The signal Sse is at 0 when the signal Se is at 0, and has a series of pulses at 1 when the signal Se is at 1. The slots at 1 have a duration t5 corresponding to the duration of the nebulization microcycles, and are separated by time intervals t6 during which the signal Sse is 0, corresponding to micropauses. The durations t5 and t6 may be identical and are for example 50 milliseconds each. As illustrated in FIG. 4C, the excitation signal Sv is applied to the transducer 44 when the signal Sse is at 1, and is not applied to the transducer when the signal Sse is at 0. During each micropause of duration t6, the liquid 43 continues to flock into the nebulizer head so that when the nebulizing head is again driven in vibration, the nebulizing head is strongly "recharged" in liquid, at the limit of the flow, and the amount of liquid nebulized during the next nebulization microcycle is greater than that which would be nebulized during the same time interval during a continuous nebulization cycle according to the prior art.

Thus, such a chopped fogging is particularly advantageous with liquids having a low surface tension (for example ethanol) or having a viscosity higher than that of water (especially heavy alcohols such as dipropylene glycol) which propagate more rapidly. slowly in the pipeline. In general, this nebulization process makes it possible to increase the efficiency of the nebulization process, both in terms of flow rate and reduction of the size of the droplets.

Thus, for a given excitation period of the transducer 44, the quantity of nebulized liquid is greater when this excitation time is minced in microcycles than when this excitation time is applied continuously to the nebulizing head. It will be appreciated by those skilled in the art that the average flow per unit time is not necessarily increased, since the micropauses lengthen the total duration of nebulization of a given amount of liquid. What is increased is the average flow rate per "unit of excitation time", that is to say the quantity of liquid nebulized for the same duration of excitation of the transducer 44.

To fix ideas, suppose that it is desired to implement the nebulization method according to the invention so that the amount of liquid nebulized during a chopper nebulization cycle of duration t3, as shown in Figures 4A to 4C, is identical to the amount of nebulized liquid during a conventional continuous nebulization cycle of duration tl, as shown in Figures 3A, 3B. In this case, the ratio t3 / t1 is given by the following relation:

t3 / tl = [(t5 + t6) / t5] / (D2 / D1)

wherein the term "(t5 + t6) / t5" is the ratio of the period t5 + t6 of the sub-template signal Sse to the duration t5 of a microcycle, and represents the correction of the cycle time which should be to account for micropauses if the average liquid flow rate during the microcycles was equal to the average liquid flow rate during the continuous nebulization cycle. The term D2 / D1 is the ratio between the average flow rate D2 per "unit of excitation time" during a microcycle and the average flow rate D1 per "unit of excitation time" during a continuous nebulization cycle, and illustrates the advantage offered by the invention.

Thus, for example, the hashing of a continuous nebulization cycle of duration t1 into microcycles having a duty ratio of 1 (t5 = t6) should in principle be compensated by multiplying by 2 the cycle time, so that the duration t3 the chopped nebulization cycle should be 2 * tl. However, as the flow of the nebulizing head is improved, the term D2 / D1 is greater than 1, for example equal to 1.5, and the duration t3 of the chopped nebulization cycle is then equal to (2 / 1.5 ) * tl for the same amount of liquid is nebulized.

Assuming, moreover, that it is desired that the quantity of nebulized liquid be constant over long periods of time covering numerous cycles of nebulization, the duration t4 of the breaks between the cycles of chopped nebulization is reduced by a duration equal to t3-t1 relative to the initial duration t2, so that the periodicity of the cycles is kept constant (t1 + t2 = t3 + t4). Finally, the nebulization method according to the invention makes it possible to improve the efficiency of the nebulizing head, that is to say the quantity of liquid nebulized for a given quantity of electricity consumed, since the quantity of electricity consumed is proportional to the excitation time of the nebulizing head. The present invention therefore makes it possible to improve the autonomy of the nebulizing device when it is powered by batteries or batteries.

Yet another advantage of the nebulization method according to the invention is that the micropauses allow the transducer 44 to cool, so that the average temperature rise of the transducer 44 during the nebulization in the ground cycle of a given amount of liquid is significantly lower. the heating of the transducer for nebulization of the same amount of liquid in a continuous cycle.

It will be apparent to those skilled in the art that this second aspect of the invention can be implemented independently of the first aspect of the invention, without applying the Ph2 overpressure to the liquid at the inlet of the nebulizing head. . According to experimental observations, the average flow rate in chopped nebulization is increased from 20% to 50% with respect to a mean continuous nebulization flow rate, with water / alcohol mixtures (for example water / ethanol or water / dipropylene glycol) and in conventional conditions of liquid supply of the nebulizing head.

This second aspect of the invention may, however, be advantageously combined with the first aspect of the invention, to combine the advantages of each. In In this case, the solenoid valve 45 is left open during the micropauses and is closed again only at the end of the chopped nebulization cycle, so that the liquid 43 can flow into the nebulization head during the micropauses, the duration of which will be chosen. even shorter because of the overpressure applied to the liquid.

FIG. 5 schematically illustrates an exemplary embodiment of the control circuit CNTCT and the excitation circuit EXCT. The CNTCT circuit comprises a microprocessor MP, a program memory PMEM in which is recorded an application program, a clock signal generator CKGEN, and an ICT circuit providing the interface between the microprocessor MP and the outside world, for example for the starting or stopping the fogger. The generator CKGEN provides a clock signal HO to the microprocessor. The circuit ICT here comprises a manual switch SWl on / off and, according to a third aspect of the invention, a manual switch SW2 to switch the nebulizer into an active standby state described below. The signals from the ICT circuit are applied to the ports P1, P2 of the microprocessor. It also includes a port P3 which provides the control signal Sg of the solenoid valve 45, and a port P4 providing the template signal Se

(Fig. 4A) Another port of the microprocessor may further be dedicated to providing a control signal of a fan (not shown) for dispersing the nebulizer jet. The EXCT circuit comprises two frequency divider circuits DIV1, DIV2, logic AND gates with two inputs A1, A2, and a voltage adapter, here an operational amplifier AMP powered by voltages V1 and V2 corresponding to the specifications of the piezoelectric transducer. 44 (Fig. 3). Frequency dividers DIV1, DIV2 are programmable by the microprocessor, both output frequency and cyclic ratio (the functional links with the microprocessor being schematized by arrows in dashed lines). The divider DIV1 receives the clock signal HO and is programmed by the microprocessor to provide a signal Hv oscillating at an excitation frequency of the transducer 44, for example 200 kHz. The signal Hv is applied to an input of the gate A2 and to the input of the divider DIV2. The latter is programmed by the microprocessor to provide a signal Hse formed by logic slots whose characteristics in duration and in cyclic ratio are identical to the characteristics desired for the sub-mask signal Sse (FIG 4B). The signal Hse and the template signal Se, are applied to the inputs of the gate A1, the output of which provides the sub-mask signal Sse. Thus, the signal Sse copies the signal Hse when the signal Se is al, and is forced to 0 when the signal Se is 0. The signal Sse is applied to the second input of the gate A2, the output of which provides a logic signal SVI. The signal SvI is applied to the input of the amplifier AMP whose output provides the signal Sv. The signal Sv is thus a signal oscillating at the frequency of the signal Hv, the envelope of which conforms to the sub-mask signal Sse, and whose amplitude is equal to Vl when the signal Hv is 1 and is equal to V2 when the signal Hv is 0. Typically, the voltages Vl and V2 are + 20V and -20V or + 40V and 0V (mass ) depending on the type of piezoelectric transducer used. When the switch SW2 is switched to the active standby position, the microprocessor MP applies to the transducer 44 excitation microcycles of very short duration, for example from 50 to 100 milliseconds, separated by pauses of very long duration, for example 30 minutes. The advantage of such an active sleep mode is it allows to periodically wet the end of the nebulizing head 40 (ejection nozzle 40-2, Fig. 3), without however consuming a large amount of liquid and without using a lot of energy. It avoids the drying of the fogging head to preserve the autonomy of the fogger in terms of liquid consumption, but also in terms of electrical energy consumed, this point being important when the fogger is electrically powered by a battery or by electric batteries.

FIGS. 6A, 6B and 6C illustrate an aspect of the invention relating to the control of the solenoid valve, and respectively represent the template signal Se, the sub-template signal Sse and the control signal Sg of the solenoid valve. which is set to 1 when the solenoid valve is to be opened. According to this aspect of the invention, the control circuit CNTCT closes the solenoid valve (set to 0 of the signal Sg) a lapse of time before the end of a nebulization cycle as defined by the template signal Se, that is before that the template signal Se does not go to 0. The time period dtl is for example of the order of 10 to 100 milliseconds, so that the pipe is no longer supplied with liquid while the last nebulization microcycle (signal Sse at 1) is performed. Such early closure has the effect of at least partially emptying the nebulizing head and avoiding the formation of a parasitic drop when the excitation of the transducer is stopped, and can be provided independently of the second aspect of the invention, c that is, the nebulization cycle is chopped or not.

Likewise, at the beginning of a nebulization cycle, the control circuit CNTCT may allow a period of time dt2 to elapse before opening the solenoid valve. This allows to wear the head of nebulization in a stabilized vibratory regime before the liquid arrives in the nebulization head, and this to prevent the liquid from flowing at the beginning of the excitation. It will be apparent to those skilled in the art that the present invention is susceptible of various other embodiments. In particular, the duration of the nebulization microcycles and micropauses can vary from milliseconds to several tens of milliseconds. These durations can be programmed by the microprocessor MP of the control circuit CNTCT as a function of the charts recorded by the manufacturer in the program memory PMEM, in order to propose to the user to specify the nature of the liquid introduced into the fogger and the flow rate. nebulization desired. For this purpose, the ICT interface circuit may be more complex than that described above and include electronic interface means rather than simple switches. This circuit can also be controlled remotely, for example via a modem. Finally, the signals Se and Sse, described above as internal control signals, may be software variables if the count of cycle times is performed by means of a routine. The present invention is capable of various applications, for example the production of a liquid nebulization device as described in application EP 0714709 or the production of a device described in application WO 00/78467, comprising a combination of several nebulizing heads for the emission of odors peaks.

Claims

Apparatus (30) for nebulizing a liquid, comprising a nebulizing head (40) comprising a capillary tube (40-1) and a nozzle (40-2) for ejecting a liquid (43), a liquid supply tank (42) (43) of the nebulization head, connected to the nebulizing head by a pipe (41), a vibrating means

(44) for driving the vibration nebulizing head to eject liquid droplets in a nebulizing jet, and excitation means (EXCT) for applying to the vibrating means an excitation signal (Sv), characterized in that it comprises means for applying to the liquid (43) at the inlet of the nebulizing head (40), during nebulization cycles, a pressure (Pr2) greater than a first pressure threshold (Patm + Shl ) beyond which the liquid flows through the fogging head when it is not driven in vibration, and below a second pressure threshold (Patm + Sh2) beyond which the liquid flows through the nebulizing head when it is driven in vibration.

2. Device according to claim 1, wherein an overpressure (Ph2) of the order of 1000 Pa to 3000 Pa is applied to the liquid at the inlet of the nebulizing head, relative to the atmospheric pressure.

3. Device according to one of claims 1 and 2, wherein the means for applying a pressure greater than the first threshold and lower than the second threshold comprises a liquid column height (H2) equal to the sum of a height (hl ) of liquid in the tank (42) and a height (h2) between the bottom of the tank (42) and the nebulizing head (40).

4. Device according to claim 3, wherein the shape of the reservoir (42) is such that the maximum height (h.2) of the liquid in the reservoir is less than one fifth of the height (hl) between the bottom of the reservoir and the nebulizing head.

5. Device according to one of claims 1 and 2, wherein the means for applying a pressure greater than the first threshold and lower than the second threshold comprises means for pressurizing the liquid present in the liquid supply tank of the nebulizing head.

6. Device according to claim 5, wherein the liquid supply tank of the nebulizing head is a deformable bag which is subjected to crushing.

7. Device according to one of claims 1 to 6, comprising a flow or pressure limiter (46) arranged in the pipe (41) between the reservoir (42) and the nebulizing head (40).

8. Device according to one of claims 1 to 7, wherein the means for applying a pressure greater than the first threshold and lower than the second threshold comprises a valve (45) arranged in the pipe (41) between the reservoir (42) and the nebulizing head (40), and means (CNTCT, Sg) for controlling the valve to close the valve when the nebulizing head is not vibrating, and opening the valve when the nebulizing head is driven into vibration.

9. Device according to claims 7 and 8, wherein the flow limiter or pressure (46) is integrated in the valve.

10. Device according to one of claims 1 to 9, comprising means (CNTCT) for controlling the excitation means (EXCT), for defining nebulization cycles interspersed with pauses during which the excitation signal (Sv) n is not applied to the vibrating means, wherein the control means is arranged to chop a nebulizing cycle into a plurality of microspheres separated by micropauses during which the excitation signal is not applied to the vibrating means.

11. Device according to claim 10, wherein the control means (CNTCT) of the excitation means are arranged to define nebulization cycles of a duration (t3) of the order of one hundred milliseconds to a few seconds, comprising nebulization microcycles with a duration (t5) of the order of a millisecond to a few tens of milliseconds.

12. Device according to one of claims 10 and 11, wherein the means (CNTCT) for controlling the excitation means are arranged to interrupt the nebulization cycles during pauses of a duration (t4) greater than the duration ( t3) nebulization cycles.

13. Device according to claim 8 and one of claims 10 to 12, wherein the control means (CNTCT) of the valve (45) do not close the valve during micropauses.

14. Device according to claim 8 and one of claims 10 to 13, wherein the control means (CNTCT) of the valve (45) are arranged to close the valve before the end of a nebulization cycle, such so that the nebulizing head (40) empties all or part of the liquid it contains before it stops vibrating.

15. Device according to one of claims 1 to 14, comprising means (CNTCT) for switching into an active standby mode comprising nebulization microcycles separated by pauses of a duration at least 1000 times longer than the duration of the microcycles , in order to wet the nebulizing head cyclically.

16. Device according to one of claims 1 to

15, comprising a main tank arranged below the liquid supply tank of the nebulizing head, and liquid transfer means from the main tank to the liquid supply tank of the nebulizing head.

17. Device according to one of claims 1 to

16, characterized in that it is arranged to nebulise a liquid in the air for the purpose of humidifying or cooling the air, or for diffusing into the air a sanitizing, deodorizing or disinfecting product, or a perfume , or a combination of these products.

18. Device according to one of claims 1 to

17, comprising a ventilation means for dispersing the nebulizing jet.