Patent Application
20190070626
Embodiments of the invention relate to the technical field of spraying devices capable of producing a fog of micro-droplets from a liquid. The droplets are generated by a piezoelectric element coupled to an acoustic concentrator. More precisely, embodiments of the invention relate to such a device comprising a detection of the level of the liquid to be sprayed.
Spraying devices capable of producing a fog of micro-droplets from a liquid by piezoelectric excitation are known per se. In these systems, the piezoelectric element can be associated with a microperforated membrane or with an acoustic concentrator in order to favor the production of fog.
In systems having a microperforated membrane, the piezoelectric transducer is coupled to a microperforated membrane, which is in contact with the liquid to be sprayed. These systems are described for example in documents WO 2013/110248 (Nebu Tec), WO 2012/020262 and WO 05/15822 (Technology Partnership), EP 2 244 314 (Zobele Holding), US 2006/213503 and US 2005/224076 (Pari Pharma), WO 2001/85240 (Pezzopane), FR 2 929 861 (L'Oréal), U.S. Pat. No. 8,870,090 (Aptar), WO 2008/058941 (Telemaq), JP 2001/300375 (Panasonic). These systems are simple and compact, but, as a general rule, their flow rate is very low, i.e., they produce a very low quantity of fog. Their useful life is rather limited (often less than 1,000 hours). They can be suitable for certain uses (for example for diffusing perfumes in a room), but not for others. Moreover, these devices require careful maintenance as the membrane risks becoming clogged. These systems are also relatively sensitive to the water pressure above the membrane and to the air pressure in the diffusion volume; problems of water leaking can appear. This lack of robustness of devices that use a perforated membrane can limit their interest for certain types of applications, in particular, industrial and especially products intended for the general public (refrigerator, electric wine cellar), which requires a substantial useful life (of about 5 to 10 years) and for which complex and frequent maintenance procedures cannot be considered.
In systems having an acoustic concentrator, the piezoelectric transducer is coupled directly to the liquid to be sprayed, with which it is in contact. More precisely, these systems, as a general rule, use a tank provided with a concentration nozzle and with a piezoelectric element, as described for example in documents EP 0 691 162 A1 and EP 0 782 885 A1 (IMRA Europe). These devices are very reliable and are commonly used to wet and to cool fresh products on sales counters, as described in documents FR 2 899 135 A1, FR 2 921 551 A1, WO 2014/023907 A1, WO 2013/034847 A1 (ARECO), FR 2 690 510 A1 (Techsonic). The flow rate is high and is suitable for many technical and industrial uses. As they do not comprise perforated membranes, these devices do not risk being disturbed in their operation by clogging problems; they have a useful life of 5,000 hours on the average. On the other hand, these devices have a significant size which is primarily linked to the thickness of water required for the correct operation of the piezoelectric element (generally from 20 to 35 mm), and also, at the height of the diffusion chamber required for the creation of an acoustic stream that is almost vertical and very powerful (generally from 40 to 100 mm).
There are devices of which the “water flow rate/electrical power” output has been optimized. These systems are generally provided with nozzles acting as concentrators of the acoustic waves generated by the piezoelectric element working at a very high frequency (of about a few MHz), a water circulation pump, a fan and a specific electrical power supply. The integration of all of these elements into a reduced volume remains a blocking point for many applications which require a system with high performance (flow rate/electrical power ratio) and very high reliability (especially the piezoelectric element, the fan, the pump, high-frequency generators, the level sensor, the filling solenoid valves).
In a misting system having piezoelectric excitation it is always necessary to monitor the presence and the volume of water in front of the piezoelectric transducer, for the following two reasons:
On the one hand, the transducer has to be protected from a lack of water, which can lead to the destruction of the piezoelectric element, especially in the cases of high electrical power absorbed. Indeed, gases (such as air) have an acoustic impedance that is much more substantial for the acoustic waves than liquids (such as water). If the piezoelectric ceramic is not covered with a liquid, the acoustic energy is therefore dissipated in the piezoelectric ceramic itself, leading to the heating thereof. If this heating is substantial or prolonged, this can lead to the degradation, and even the functional destruction of the piezoelectric element.
Good stability of the misting density over time must also be guaranteed; this aspect is particularly important in applications that require a very precise and controlled level of humidity.
The lack of water can be momentaneous, for example, when the level of water of the system moves following the permanent or occasional movement of the system; this problem can arise for misting systems on board vehicles. The lack of water can also be linked to the lack of supply with water. The resupplying with water can be automatic or manual. However, it is known that the flow rate of the fog generated by the system depends, for an equal dissipated power, on the level of water above the piezoelectric element.
In order to respond to these problems, most misting systems having piezoelectric excitation are provided with a water level sensor. These sensors can be of the optical, capacitive, ultrasound, electromechanical, magnetic, etc. type. They typically have a problem of congestion, precision, price and reliability. More precisely: the congestion of the sensor can become a problem in miniaturized systems. The precision must become a problem because many level sensors have a low trigger point and a high trigger point. The price can become a problem in the case of miniaturized systems which open new applications with the condition of being inexpensive. The reliability can become a problem due to the inevitable clogging of the active surface of the sensor.
The problem that this invention seeks to resolve is to present a misting system having improved piezoelectric excitation, which has better reliability, allows for a more compact construction, less expensive, and a better adjustment precision, and which lends itself, in particular, to miniaturized systems.
To this effect, embodiments of the invention have for object a misting device having piezoelectric excitation, comprising:
this device being characterized in that it further comprises:
According to other characteristics of this misting device, taken separately or according to any technically compatible combination:
Embodiments of the invention also have for an object, a method for implementing a listing device such as defined hereinabove, comprising:
this method comprising the following steps:
According to other characteristics of this method, taken separately or according to any technically compatible combination:
The inventors have found that the problem posed can be resolved surprisingly without having recourse to a liquid level sensor, by using the piezoelectric element itself as a means for detecting the liquid. Indeed, the inventors have observed a link between the characteristics of the misting stream and the current consumption of the piezoelectric element.
According to embodiments of the invention, a parameter representative of the current consumed by the piezoelectric element is measured. This parameter can be the consumed current itself. As an alternative, this can be a magnitude, such as the voltage, from which those skilled in the art can access the current consumed.
The piezoelectric element 20 generates ultrasound waves 40 which are transmitted in the direction of the acoustic concentrator 30. The acoustic concentrator 30 can have a parabolic or other shape; the focal point of the acoustic concentrator 30 here bears the reference 50. The acoustic concentrator 30 is advantageously made from a hard material (for example, metal) that can reflect ultrasound waves. The frequency of the ultrasounds used in the framework of this invention lies advantageously between 1.3 MHz and 3 MHz, it can be for example 1.68 MHz.
In normal operation of the system 1, the active surface 21 of the piezoelectric element 20 is entirely covered with liquid and the ultrasound waves 40 are transmitted in the liquid where they impact against the surface of the acoustic concentrator 30. The acoustic concentrator 30 is designed in such a way, and the liquid level is adjusted in such a way, that the focal point 50 of the ultrasound waves 40 lies slightly below the liquid level Iopt. This provides a stable misting stream 70 and a maximum generation of fog 60. In the case of
The inventors have observed that this heating modifies the electrical consumption of the piezoelectric element 20, as shall be detailed in reference to
Typically, in a misting system having piezoelectric excitation, the piezoelectric element 20 is powered by pulse trains at a fixed voltage, with these pulses being close to the resonance frequency of the piezoelectric element 20. When the current absorbed by the piezoelectric element 20 is measured, it is observed that this current increases with the temperature. By way of example, in a misting system having piezoelectric excitation, the piezoelectric element was powered with a voltage of 12 volts and the current absorbed was 400 mA in normal operation; this current is 440 mA when a portion of the active surface of the piezoelectric element is not submerged.
Surprisingly, the inventors have observed that when the non-submerged portion of the active surface of the piezoelectric element 20 increases, the current absorbed decreases and changes to a value close to zero in the total absence of liquid (
When the liquid covers the entire height of the surface, the consumed current has a value referred to as optimal Iopt, which can also be found when the liquid is present in excess (right portion of the curve corresponding to the values 110 and 120). When the liquid level decreases, the value of the current consumed increases slightly, from the optimum value Iopt hereinabove to a value referred to as intermediate Iint. This value of consumed current is then substantially constant as the liquid level drops, until dropping substantially to a value referred to as critical Icrit which corresponds to an empty liquid tank.
There are therefore three characteristic values of consumed current according to the water level, which correspond to three states of the device: optimal when the liquid level is satisfactory, intermediate when the liquid level is insufficient but the integrity of the piezoelectric element is not called into question, and finally critical when there is no longer any liquid in the tank. Typically, Iint is slightly greater than Iopt, by 10 to 20%, while Icrit is much less than Iopt.
In all of these embodiments of this invention said liquid can be water, possibly comprising substances (ionic or non-ionic) in solution or in dispersion. For example, the water can include one or several organic products, miscible or not, such as an alcohol or an essential oil.
Each one of the curves, representing an operation mode, shows the linearity between the voltage applied to the terminals of the piezoelectric element 20 and the consumed current. It follows that this variation in the current consumption according to the liquid level cannot be used directly to detect the liquid level: a calibration must be carried out.
In the case of a high-power electronic circuit where a signal generator supplies the piezoelectric element at a fixed frequency it is observed that the current at the supply of the circuit varies according to the surface fraction of the active surface of the piezoelectric element that is covered with water.
In a typical embodiment, the piezoelectric element is powered with direct current (for example with a voltage of 24V DC), modulated by the resonance frequency of the piezoelectric element. In such a normal operating mode, the active surface of the piezoelectric element is entirely covered with liquid; the misting operates, and the current consumption is stable (typically at about 2.3 A for a diameter of the active surface between about 10 mm and about 20 mm).
In the case where the active surface of the piezoelectric element is only partially covered with liquid, the inventors have observed a drop in the current which is significant and extremely fast (in less than 100 ms). This drop can be about 30 to 40% of the nominal value of the current absorbed by the piezoelectric element entirely covered with liquid (in the example about 2.3 A). These indicators make it possible to react quickly in order to cut off the power supply of the piezoelectric element or to decrease the electric power supplied by said power supply to the piezoelectric element, and/or to trigger another filling with water. As such it is possible to return to an operating mode in which the active surface is completely submerged.
This indicator, which is connected to the drop in current observed, can be correlated with a temporal measurement in order to estimate the rate of misting of our system and to possibly trigger alarms in the case of a problem due to the filling or to the correct operation of the piezoelectric element.
An illustration of such a method for regulation is described here. The first three steps are typically implemented during the first use of the device. Indeed, the characteristics intrinsic to the various piezoelectric elements can vary from one device to the other. These steps make it possible to access the knowledge of these characteristic.
1st Step: Calibration of the Parameters in the Optimal Presence of the Liquid.
The voltage A is made to vary by a minimum service value to a maximum service value (for example from 6V to 12V), the value of the current B for each voltage is measured and recorded. These values will be used as a reference to detect the variation of the current during the misting and to indicate to the users the presence of the absence of water.
2nd Step: Calibration of the Parameters in the Intermediate Presence of the Liquid.
The voltage A is made to vary between the minimum and maximum service values hereinabove, the value of the current B for each voltage is measured and recorded. These values will be used as a reference to detect the variation of the current during misting and to indicate to the users the presence or the absence of water.
3rd Step: Calibration of the Parameters in the Absence of Liquid.
The voltage A is made to vary between the minimum and maximum service values hereinabove, the value of the current B for each voltage is measured and recorded. These values will be used as a reference to detect the variation of the current during misting and to indicate to the users the presence or the absence of water.
4th Step: Configuration of the System
The various values of consumed current for each voltage observed are recorded in the control means of the piezoelectric C. As such, pour each value of voltage at which the device can be put into service, in particular the values Iopt, Iint and Icrit are recorded such as defined hereinabove.
In the example indicated hereinabove (self-oscillating circuit), when it is powered with 12 Volts, the consumption Iopt of the piezoelectric element is 400 mA for a normal operation. This consumption increases to a value Iint in the neighborhood of 440 mA in operation with a low liquid level, then this current consumption falls to a value Icrit in the neighborhood of 110 mA in the absence of liquid as shown in
5th Step: Normal Operation.
The value of the current consumed by the piezoelectric element is measured. This measurement can be continuous or, alternatively, it is possible to take regular measurements at a suitable frequency. As long as the instantaneous value of this current I does not reach the threshold value such as shown in
6th Step: Supplying with Water
The regulation system C makes it possible to control the solenoid valve E providing the filling of the tray R when the current consumption of the piezoelectric 20 becomes excessive. More precisely, when the measured instantaneous value of current consumed reaches the threshold value Iint defined hereinabove, the regulation system triggers an alert which is directed towards the solenoid valve E. The latter then controls the inlet of additional liquid into the tank, which has for effect to lower the value of the current consumed. The device returns to an optimum configuration, such as defined hereinabove, in such a way that the inlet of water is then stopped.
As an alternative, the alert triggered by the regulation system may not be transmitted to a solenoid valve, but to a signaling member. The latter then transmits a signal that can be perceived by the user, in particular of the visual and/or audible type. The adding of liquid into the tank is, in this case, directly provided by the user, not by a mechanical element of the device.
7th Step: Notification of a Lack of Water and Stoppage
The regulation system C is able to stop the piezoelectric in order to limit breakage of the latter when it detects a low consumption of current by the piezoelectric element 20.
More precisely, when the measured instantaneous value of current consumed reaches the threshold value I Icrit defined hereinabove, the regulation system triggers an alert which is directed towards the means for automatically cutting off the piezoelectric element. This makes it possible to guarantee the mechanical integrity of this element, which would be placed in danger if this situation of absence of water were to be prolonged.
As an alternative, the alert triggered by the regulation system may not be transmitted to means for cut-off, but to a signaling member. The latter then transmits a signal that can be perceived by the user, in particular of the visual and/or audible type. The stoppage of the piezoelectric element is, in this case, directly provided by the user, not by a mechanical element of the device.
As described hereinabove, in the sixth and seventh steps, both the need for a supply with water and the need to cut off the piezoelectric element can be reported directly to the user. In this case, two different signals are advantageously provided, respectively for the need for water and the stoppage of the piezoelectric element. It is possible to use two different signaling members or, as an alternative, a single member able to transmit two different signals.
This board is constructed around the microcontroller 200 allowing for the application management of the steps mentioned hereinabove. This microcontroller 200 also manages the connectivity of the input/output modules.
This board comprises an all-or-nothing (AON) analog input module 210 and an output module 220. These assemblies make it possible to control the supply of water of the container in case of an intermediate or empty level or to control the information signal that makes it possible to inform the user of the need to fill the tank that supplies the container.
A subassembly 230 is present to form the piezoelectric control 25, this makes it possible to define the excitation frequency, the voltage, the duty cycle. This module also makes it possible to obtain the information on the current consumed 260 as well as the temperature 270 of the piezoelectric 20.
The last module 240 of this board 190 is the checking and control element of the piezoelectric. This module is the interface allowing for the sending of the voltage signal that makes it possible to excite the piezoelectric 20 and in return to obtain the temperature of said element 20.
Embodiments of the invention is shown hereinbelow via examples that however do not limit the scope thereof. This example concerns an implementation of the power control module of the piezoelectric.
In order to carry out the method of regulation, those skilled in the art need to understand the technical aspect linked to the module 240 of
In
The principle of the driver (120) is to be able to supply for a short instant the substantial current required for the switching of the transistor 130 to high frequencies. During the control signal edges, the inrush current of the control of the transistor 130 is very high, and providing enough current allows for a fast switching, which limits the transient states that cause a heating of the transistor 130.
In order to be able to rapidly supply a substantial current, the transistor driver 120 uses several capacitors in parallel upstream of the component. The control voltage of the transistor is set to 12V, as such minimizing the effect of its Ron characteristic and therefore the heating of the component.
The excitation frequency of the piezoelectric 20 is generated by the component 110, which produces a square signal with a programmable frequency (by default 1.7 MHz). The circuit for adapting the impedance 140 of the piezoelectric 20 is comprised of a coil and a capacitor in series with a capacitor in parallel on the output.
The relation between the values of these components (L and C) is a very important factor in the behavior of an LC circuit and are chosen taking account of the impedance of the piezoelectric element (in water) and of its resonance frequency, and which will fix in what follows its average current consumption.
The resultant is a stable and constant sinusoidal signal according to time at the terminals of the piezoelectric element adapted to an optimum operation in water. (The values of the peak-to-peak voltages/current must not exceed the max limit of the piezoelectric element).
f0: the resonance frequency.
L: the value of the coil.
C: the value of the capacitor.
For an operation without water, the value of the impedance of the piezoelectric element will change and introduce an electrical impedance mismatch for all of the circuit and will change in what follows its current consumption.
The piezoelectric 20 is controlled by a transistor 130, that has an excellent command load ratio and resistance at the off state, and a very fast response time that allows it to operate at a high frequency (1.7 MHz), that makes it possible to have both a quality signal and moderate heating.
In order to provide the fastest switching possible and therefore to limit the heating of the transistor, which is very substantial during the transition phases, a control driver 120 that can deliver up to 2×5 A is placed upstream.
The current measurements 150 are taken using a shunt resistor with a low value, between 0.01 and 0.1 ohm according to the current consumed, and a component of the voltmeter type measuring the difference in potential at the terminals of the resistor and multiplying by 10 the result in order to have a value that is more legible for the microcontroller.
The microcontroller in what follows will compare the values of current taken in order to define the operating state of the piezoelectric. This state will make it possible to validate the step of the method.
The following numerical references are used in this description:
| Number | Date | Country | Kind |
|---|---|---|---|
| 1502493 | Nov 2015 | FR | national |
The present application is a National Stage Application of PCT International Application No. PCT/FR2016/053138 (filed on Nov. 30, 2016), under 35 U.S.C. § 371, which claims priority to French Patent Application No. 1502493 (filed on Nov. 30, 2015), which are each hereby incorporated by reference in their respective entireties.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/FR2016/053138 | 11/30/2016 | WO | 00 |
