Device for producing liquid foam

Abstract

The present invention relates to a device for producing foam of a liquid, comprising: a liquid source; an air or other gas source; a mixing device in fluid communication with the liquid source and the air source, adapted to mix the liquid with the air to produce foam of the liquid; a conduit in fluid communication with the mixing device, the foam flowing along the conduit in a flow direction. The device for producing foam comprises a foam sensor associated with the conduit, comprising a radiation source adapted to produce radiation irradiating the conduit along an irradiation direction incident on the flow direction. The foam sensor further comprises: a first photodiode, which is placed in the irradiation direction from a side opposite to the radiation source with respect to the conduit, the first photodiode producing a first electrical signal based on a portion of the radiation passing through the foam flowing along the conduit; and a second photodiode, which is placed in a diffusion direction substantially perpendicular to the irradiation direction, and producing a second electrical signal based on a portion of the radiation diffused by the foam substantially along the diffusion direction.

Description

Technical Field

[0001] The present invention relates to a device for frothing a liquid, in particular an edible liquid such as milk, coffee or the like, and to a froth sensor with which such a device may be equipped. Background Art

[0002] To date, the coffee industry has been expanding both in public places (such as bars and restaurants) and in domestic environments due to the widespread use of coffee machines starting with coffee beans or ground coffee in bulk and capsule form.

[0003] In the coffee world, milk is a strategic drink as it is used to prepare many coffee-based drinks such as cappuccino or coffee macchiato.

[0004] Milk is often used as a "foam", that is, "froth". For example, a cappuccino is a hot drink consisting of a dose of espresso added to a dose of frothy hot milk.

[0005] In this context, foam can be defined as a two-phase colloidal system in which air bubbles are dispersed in a liquid phase consisting of milk.

[0006] The characteristics of the foam layer present on top of a beverage contribute greatly to the overall quality of the beverage and the consumer's appreciation of it. In fact, many characteristics of the beverage itself depend on the quality of the foam, such as aesthetics, volume, consistency and mouthfeel. The way in which the aroma of the coffee is released also depends on the quality of the foam.

[0007] One of the most important properties of milk foam is physical stability. In fact, for drinks like cappuccino, foam stability is essential for the duration of the consumption time, which usually lasts 10 / 15 minutes. In the literature, Kamath et al. (2008a) and Borcherding et al. (2008a) describe the changes in the appearance of skim milk foam according to the holding time after foaming. Therefore, the distribution of bubbles, the size of the bubbles and the changes in shape they undergo depend on the stability of the bubbles in the foam.

[0008] The stability of bubbles in a foam is defined by three processes: (i) coalescence of bubbles; (ii) disequilibrium of bubbles; and (iii) drainage of liquid from the foam. Prins (1986) and Walstra (2003) discussed the above processes in detail and are summarized below.

[0009] The coalescence of bubbles reduces the number of bubbles in the foam and increases the size of the bubbles in the foam. The driving force behind the coalescence of bubbles is the stability of the liquid film between the droplets. In particular, the presence of fat in milk plays an important role in determining the stability of the liquid film, since surfactant substances originating from a drop of emulsion diffuse to the surface of the liquid film and stabilize the air bubbles. The size of the bubbles plays an important role in their subsequent coalescence.

[0010] In particular, bubbles with a size between 2 and 4 microns are particularly susceptible to coalescence.

[0011] The unevenness of the bubbles causes the bubbles to coalesce as the gas flows from smaller bubbles (at higher pressure) to larger bubbles. As a result, the smaller bubbles become smaller, while the larger bubbles become larger. Therefore, it is necessary to be able to check the uniformity of the diameter of the air bubbles present in the foam.

[0012] Regarding the expulsion of liquid from the foam, it can be described as an upward movement of the bubbles, i.e. "skimming", which is a result of the density difference between the air bubbles and the continuous phase; at the same time, the continuous phase between the bubbles undergoes a downward movement. In order to prevent instabilities caused by the expulsion of liquid from the foam, it is necessary to prevent the upward movement of the air bubbles. Increasing the viscosity of the surrounding liquid does not prevent the expulsion of liquid, but it significantly reduces the expulsion rate. Therefore, it is important to know the viscosity of the ingredients used in order to adjust the recipe for preparing the foam accordingly.

[0013] Especially in public places, the "foaming" operation of milk is usually done manually by the bartender directly using a steam wand. The steam wand allows the introduction of air into the milk in the form of bubbles. However, this operation requires some care, since the whey proteins present in the milk are surfactants but also thermolabile compounds. The activity of the surfactants facilitates the frothing of the milk when air is introduced, by reducing the surface tension of the fluid and thus its surface hardness. On the other hand, thermolabile properties determine the existence of a limit temperature, which in the case of milk is about 70°C, above which the whey proteins irreversibly deteriorate and lose their surface activity. By cooling the milk again below this temperature, the whey proteins no longer regain their surfactant properties.

[0014] The existence of the above-mentioned limit temperatures is well known to the most professional operators in this field. Vice versa is also true. When inexperienced operators encounter difficulties in obtaining milk frothing, they usually insist on using a steam wand in an attempt to obtain the desired frothing. In this way, the milk is heated above the limit temperature and often boiled. The increase in temperature and the decomposition of a large part of the protein substances cause, on the one hand, an increase in the surface tension and, on the other hand, boiling of the milk, which leads to the formation of a foam consisting of very large bubbles that tend to disappear after a very short time.

[0015] There are also automatic or semi-automatic devices for making milk foam, which usually use a mixing device to mix milk with air to make such foam. The mixing device may, for example, include:

[0016] - the steam wand for manual milk frothing type as above,

[0017] - a pump designed to suck in milk and air and to mix the milk and air to obtain foam;

[0018] - a stirring member, possibly heated, which mixes the milk in the container to obtain froth.

[0019] Whether it is done manually or using automatic devices, the control of the process used to obtain the foam is very complex, precisely because of the inherent instability of the foam itself. The formation and persistence of the foam depends on many factors related to the process used to obtain the foam (as described above) and the nature, quality, composition and storage conditions of the milk.

[0020] Good milk foam must have such a size of air bubbles that it is barely visible to the naked eye, that is to say, of the order of a few micrometers in diameter, and it must be silky, with good consistency, persistence and fluidity.

[0021] Currently, there are several parameters available for assessing the quality of milk foam, among which the following can be mentioned: "foamability", "foam stability", "air bubble size", "overrun".

[0022] Currently, there are laboratory instruments that are able to analyze foam produced in special transparent cylinders to obtain information about its properties. Said laboratory instruments usually utilize conductivity measurements or high-quality video image acquisition.

[0023] However, to date, there is no device or method for producing milk froth that enables a consistent and reproducible froth having the desired quality characteristics to be obtained.

[0024] For example, the foaming effect of milk also depends largely on the different types of milk processed (e.g., whole milk, skim milk, part skim milk, long-life milk). In addition, soy milk is becoming increasingly popular, which is difficult to foam and requires specific operations that are different from those for frothing milk of animal origin.

[0025] Furthermore, as is well known, the presence of a surface foam layer is currently very much appreciated and increasingly in demand, even in espresso or weak coffee without milk. Even obtaining coffee foam has similar disadvantages as those described above with specific reference to milk foam. Summary of the invention

[0026] The main task of the present invention is to realize a device for frothing liquids, in particular edible liquids such as milk, coffee and the like, which overcomes the drawbacks and limitations of the prior art and allows measuring the quality characteristics of the froth.

[0027] Within the scope of this task, an object of the invention is to create a device for producing foam which allows regulating the process for producing the foam itself in order to ensure that it is produced with the desired quality properties.

[0028] Another object of the invention is to achieve a device for producing foam that allows obtaining information on the presence, distribution and type of bubbles forming the foam, in order to guarantee the stability and repeatability of the pattern used to obtain the foam itself.

[0029] Indeed, as mentioned in the introduction, since the perception of the quality of a drink is greatly influenced by the quality of the foam present on top of the drink itself, knowing the properties of the foam and possibly modifying them when necessary is very important for producing high quality drinks in a reproducible and constant way.

[0030] Another object of the invention is to realize a device for producing foam which is easy to manufacture and economically competitive if compared with the prior art.

[0031] The aforementioned tasks, as well as the aforementioned and other purposes that will become more apparent hereinafter, are achieved by the device for producing foam of liquid described in the present application, in particular, the device for producing foam of edible liquids such as milk, coffee and the like, and the foam sensor for such a device described in the present application.

[0032] Other features are also contemplated in this application. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Further features and advantages will become more apparent from the description of a preferred but not exclusive embodiment of a device for producing liquid foam, in particular foam of edible liquids such as milk, coffee and the like, which is illustrated in a non-limiting manner only with the aid of the accompanying drawings, in which:

[0034] Figure 1 is a schematic diagram of an embodiment of an apparatus for generating foam according to the present invention;

[0035] Figure 2 According to the present invention Figure 1 A schematic diagram of a variation of the device for generating foam;

[0036] Figure 3Schematically illustrates the working principle of a foam sensor present in a device for generating foam according to the present invention;

[0037] Figure 4 is a schematic diagram of a foam sensor present in a device for generating foam according to the present invention;

[0038] Figure 5 is a schematic diagram of a variant of a foam sensor according to the invention present in a device for generating foam. DETAILED DESCRIPTION

[0039] With reference to the aforementioned figures, a device for producing foam of a liquid (particularly an edible liquid such as milk, coffee or the like) is indicated as a whole by reference numeral 1 and comprises:

[0040] - a liquid source 13, such as preferably milk or a milk-based liquid, or coffee;

[0041] - air source 11 or other gas source,

[0042] - a mixing device 3, which is in fluid communication with the liquid source 13 and the air source 11, suitable for mixing the liquid from the liquid source 13 with the air from the air source 11 so as to produce a foam of said liquid;

[0043] a duct 7 which is in fluid communication with the mixing device 3 downstream of the mixing device 3 itself, along which duct 7 the foam flows out of the mixing device 3 according to a flow direction S.

[0044] The mixing of air and liquid by means of the mixing device 3 allows the introduction of air in the form of gas bubbles into the liquid in order to obtain foam.

[0045] Advantageously, as will also be explained better below, the air source 11 can be constituted by the environment itself, ie by ambient air which reaches the mixing device 3 for example via an inlet.

[0046] Foam according to Figure 3 and Figure 4 The flow direction indicated by S in FIG. 7 is along the conduit 7 .

[0047] According to the invention, the device 1 for generating foam of a liquid comprises a foam sensor 100 associated with the conduit 7. The foam sensor 100 comprises a radiation source 101 adapted to generate radiation 103 which strikes the conduit 7 along an irradiation direction R incident on the flow direction S.

[0048] According to the present invention, the foam sensor 100 comprises:

[0049] a first photodiode 105 arranged in the irradiation direction R from the side opposite to the radiation source 101 with respect to the conduit 7. The first photodiode 105 generates a first electrical signal 106 as a function of a radiation portion 107 passing through the foam flowing along the conduit 7, or, instead of the first photodiode 105,

[0050] a second photodiode 109 arranged along a diffusion direction D substantially perpendicular to the irradiation direction R, said second photodiode 109 generating a second electric signal 110 as a function of a radiation portion 111 diffused substantially along said diffusion direction D by the foam.

[0051] Preferably, the foam sensor 100 includes both the first photodiode 105 and the second photodiode 109 .

[0052] The expression "flow direction S" refers to the direction in which the foam flows inside the duct 7 (in particular the portion of the duct 7 irradiated by the radiation 103 emitted by the radiation source 101). In the case that the duct 7 (in the portion of the duct 7 irradiated by the radiation 103) has a straight trend, the flow direction S coincides with or is parallel to the central axis of the duct 7. In the case that the duct 7 (to be precise the portion thereof irradiated by the radiation 103) has a curvilinear trend according to a curve, the expression "flow direction S" refers to the direction tangent to the curve in the vicinity of the area of ​​the duct 7 irradiated by the radiation 103.

[0053] The term "incident" means that the flow direction S and the radiation direction R have a common point, that is to say they intersect so as to define an angle greater than 0°.

[0054] Preferably, the angle of incidence between the flow direction S and the irradiation direction R is substantially equal to 90°.

[0055] Advantageously, the conduit 7 is transparent to the radiation 103 , at least in the portion illuminated by the radiation 103 emitted by the radiation source 101 .

[0056] The radiation 103 emitted by the radiation source 101 may be radiation in the infrared, visible or ultraviolet spectrum.

[0057] Radiation source 101 may include Figure 4 A photodiode 102, or laser source, is shown schematically.

[0058] Advantageously, the radiation source 101 may comprise collimating optics 112 .

[0059] Advantageously, the foam flowing along the duct 7 can reach the open end of the duct 7 and be collected in the container body 9. The container body 9 can for example be constituted by a coffee or cappuccino cup, possibly already filled with coffee, or by a pot collecting milk foam to be added to coffee or cappuccino.

[0060] Advantageously, the device 1 for generating foam comprises a processing and control unit 15 connected to the foam sensor 100 so as to receive and process the first electrical signal 106 generated by the first photodiode 105 and / or the second electrical signal 110 generated by the second photodiode 109. Said processing and control unit 15 is configured to regulate the actuation of the mixing device 3 based on said first electrical signal 106 and / or said second electrical signal 110.

[0061] Thus, the processing and control unit 15 may be configured to intervene in the operation of the mixing device 3 so as to increase or decrease the addition of air to the edible liquid depending on the characteristics of the foam detected by the foam sensor 100 .

[0062] For example, if the foam sensor 100 detects a lack of air bubbles, ie an excess of liquid phase in the foam, the control unit 15 may intervene in the operation of the mixing device 3 to increase its activity.

[0063] Advantageously, the mixing device 3 comprises a pump 30 suitable for sucking liquid from the liquid source 13 and air from the air source 11 .

[0064] The pump 30 may be a gear pump.

[0065] Alternatively, the pump 30 may be a twin screw pump, for example similar to the pump described in patent EP3305145.

[0066] Therefore, the pump 30 performs a function of pumping liquid and air and a function of mixing the liquid and air to generate foam.

[0067] As is known, over time, the performance of pumps tends to decline, in particular the priming performance, so that air is sucked into the pump, affecting the formation of foam. The presence of the foam sensor 100 (by detecting the reduction of the gas phase in the foam) makes it possible to intervene by increasing the number of revolutions of the pump 30 by means of the processing and control unit 15, thus compensating for the normal wear of the pump itself and keeping the characteristics of the foam produced constant.

[0068] Advantageously, the device 1 for producing foam comprises a filter of the air sucked in by the pump 30 .

[0069] As is known, such an intake air filter tends to clog over time, thus affecting the formation of foam. In this case as well, the presence of the foam sensor 100, by detecting the reduction of the gas phase of the foam, allows compensating for the reduction in the inflow of air, for example by increasing the number of revolutions of the pump 30 in order to draw more air.

[0070] Furthermore, in the event that the liquid source 13 is depleted, the foam sensor 100 will detect over-inflation of the produced foam, which may generate a warning signal for replenishing the liquid source 13 via the processing and control unit 15 .

[0071] In an embodiment of the device 1 for generating foam which is not shown in the drawings, the mixing device 3 comprises an agitator member capable of agitating the liquid in order to introduce ambient air and thus form foam.

[0072] The agitator member may be inserted inside a container body adapted to also contain a liquid.

[0073] Alternatively, the agitator member may comprise a vibrating element arranged inside a conduit in which a liquid flows, which, when vibrated, turns into foam.

[0074] Advantageously, the device 1 comprises a proportional valve 17 associated with the air source 11 and connected to the processing and control unit 15. The processing and control unit 15 is configured to operate said proportional valve 17 so as to adjust the flow rate of air from the air source 11 based on the first electrical signal 106 and / or the second electrical signal 110.

[0075] For example, if the foam sensor 100 detects a lack of air bubbles in the foam, the processing and control unit 15 may intervene in the opening of the proportional valve 17 in order to allow a greater air flow to the mixing device 3, thereby forming the foam more effectively.

[0076] If, on the contrary, the foam sensor 100 detects the presence of too many air bubbles and of too large a size, the processing and control unit 15 can intervene in the opening of the proportional valve 17 in order to reduce the flow of air to the mixing device 3 .

[0077] Advantageously, the conduit 7 through which the foam flows comprises a portion 8 downstream of the mixing device 3 and upstream of the foam sensor 100. The portion 8 is configured to generate a distributed pressure drop of the foam and is therefore suitable for stabilizing the foam structure before the foam passes the foam sensor 100.

[0078] Advantageously, the device 1 for producing foam also comprises heating means 21 of the foam and / or the edible liquid, which are also connected to the processing and control unit 15. Said processing and control unit 15 is thus configured to regulate the temperature of the foam and / or the liquid by means of said heating means 21.

[0079] like Figure 1 As shown, heating means 21 may be associated with the liquid source 13 and thus be adapted to heat the liquid and, therefore, the foam formed by the mixing means.

[0080] As explained in the introduction, the temperature of the liquid, especially in the case of milk, is a very important factor in giving the foam the desired quality properties.

[0081] The processing and control unit 15 thus allows regulating the activation of the heating means 21 , and therefore the heating of the liquid, based on the electrical signals 106 and / or 110 detected by the foam sensor 100 .

[0082] For example, the heating means 21 may comprise a heating plate 210 associated with a container constituting the liquid source 13. Alternatively, the heating means 21 may comprise a resistor associated with the liquid source 13.

[0083] like Figure 2 As shown in , the heating device 21 may alternatively be placed substantially at the point where the foam is delivered to the container 9. Said heating device 21 may be placed upstream or downstream of the foam sensor 100 and is basically adapted to heat the already formed foam.

[0084] The heating device 21 may comprise a steam heater 211 , for example of the type described in patent EP3248519.

[0085] Advantageously, the device 1 comprises a temperature sensor 23 and / or a pressure sensor 25, the measurement data of which can be combined with the measurement data obtained by the foam sensor 100, in order to further more accurately measure the quality of the foam.

[0086] Advantageously, a temperature sensor 23 and / or a pressure sensor 25 are connected to the processing and control unit 15 .

[0087] The temperature sensor 23 is adapted to detect the temperature of the foam, preferably at the conduit 7 , even more preferably near the point where the foam is delivered to the container 9 .

[0088] The foam temperature is a parameter that can be used to adjust the activation of the heating device 21 in order to obtain a foam at a desired operating temperature.

[0089] Advantageously, the processing and control unit 15 can also take into account the foam temperature detected by the temperature sensor 23 , possibly correlated with the measurement made by the foam sensor 100 , in order to regulate the actuation of the mixing device 3 .

[0090] The temperature sensor 23 is preferably a thermopile type sensor.

[0091] The temperature sensor 23 provides information about the foam temperature, which helps control the volume of the bubbles in the foam. In fact, high temperatures increase the internal air pressure, making the foam bubbles unstable.

[0092] Furthermore, the temperature of the milk foam and / or the milk itself is a parameter of the recipe for preparing the drink, so that the detection of the temperature is useful not only for the generation of the foam but also for the optimal preparation of the end product.

[0093] Advantageously, the pressure sensor 25 allows knowing the pressure in the duct 7 or in other ducts of the frothing device 1 , so as to be able to define an algorithm for detecting the quality of the froth that is more precise and independent of the flow rate of the beverage with the froth.

[0094] Advantageously, if Figure 4 and Figure 5 As shown, the foam sensor 100 includes: a housing 113 , which is penetrated by the conduit 7 and accommodates the internal radiation source 101 , the first photodiode 105 , the second photodiode 109 ; and a processor and controller 15 .

[0095] exist Figure 4 , the second photodiode 109 is shown in dashed lines, meaning that it is placed at a different height compared to the first photodiode 105 .

[0096] Preferably, if Figure 4 As shown, the foam sensor 100 comprises a temperature sensor 23 and / or a pressure sensor 25. Advantageously, in fact, the temperature sensor 23 and / or the pressure sensor 25 can be housed in the housing 113 of the foam sensor 100.

[0097] exist Figure 5 , the housing 113 is substantially annular in shape.

[0098] Advantageously, the radiation source 101 , in addition to the two photodiodes 105 and 109 , is also electrically connected to a processing and control unit 15 .

[0099] Advantageously, the processing and control unit 15 is configured to sample the electrical signal generated by the first photodiode 105 and / or the second photodiode 109 at a frequency greater than 8 kHz. In this way, the sampled signal retains a large amount of information. Preferably, the sampling frequency is between 30 KHz and 70 KHz, even more preferably, it is about 50 KHz. This also keeps the size of the detected data file acceptable.

[0100] Said sampling frequency is particularly suitable for acquiring the signal generated by the passage of the foam along a conduit 7 having a diameter less than 10 mm, preferably between 3 mm and 7 mm.

[0101] In case the diameter of the conduit 7 is less than 5 mm, a higher sampling frequency is preferred. Furthermore, the lower the average flow velocity of the foam in the conduit, the lower the sampling frequency of the signal.

[0102] Advantageously, the liquid source 13 may comprise a container 130 suitable for containing a liquid. The internal volume of said container 130 is advantageously in fluid communication with the mixing device 3 via a duct 131. Advantageously, a non-return valve 132 is associated with said duct 131.

[0103] Advantageously, the air source 11 may comprise an inlet constituted by a proportional valve 17, which is in fluid communication with the mixing device 3 through a duct 115. Advantageously, a non-return valve 112 is associated with said duct 115.

[0104] Advantageously, the conduit 131 from the liquid source 13 and the conduit 115 from the air source 11 are connected to each other via a T-shaped connector 18, which enables a first mixing of the liquid and the air.

[0105] Specific reference Figure 2 In the illustrated embodiment, a second T-shaped connector 19 may also be provided between the steam heater 211 and the conduit 7 .

[0106] The invention also relates to a foam sensor 100 associated with a conduit 7 in which a foam of a liquid obtained by mixing the liquid with air or another gas flows according to a flow direction S.

[0107] According to the present invention, the foam sensor 100 comprises:

[0108] a radiation source 101 suitable for generating radiation 103 which irradiates the conduit 7 along a radiation direction R incident on the flow direction;

[0109] a first photodiode 105 arranged in the irradiation direction R from the side opposite to the radiation source 101 with respect to the conduit 7, the first photodiode 105 generating a first electrical signal 106 as a function of a radiation portion 107 passing through the foam flowing along the conduit 7, or alternatively,

[0110] a second photodiode 109 arranged along a diffusion direction D substantially perpendicular to the irradiation direction R, the second photodiode 109 generating a second electrical signal 110 as a function of a radiation portion 111 diffused by the foam substantially along the diffusion direction D,

[0111] Advantageously, the foam sensor 100 includes both the first photodiode 105 and the second photodiode 109 .

[0112] The foam sensor 100 may also have one or more of all the technical features already described with reference to the device 1 for generating foam.

[0113] Advantageously, the foam sensor 100 is associated with the duct 7 of the device 1 for generating foam as described above.

[0114] The foam sensor 100 can in any case be associated with any device for generating foam, as long as there is a region in the device through which the foam can flow, such as, for example, the duct 7 .

[0115] The operation of the device for generating foam is briefly described below, particularly with regard to the presence of a foam sensor.

[0116] A first photodiode 105 (aligned with the radiation source 101 along the irradiation direction R, but on the opposite side of the conduit 7) detects the shadows caused by the passage of bubbles present in the foam and thus generates a "photogenerated" current, which is greater the smaller the number and size of the bubbles present in the foam.

[0117] The passage of a bubble actually involves an attenuation of the radiation passing through the liquid flowing along the duct 7 , and therefore involves a variation in the current signal generated by the first photodiode 105 .

[0118] The second photodiode 109 , arranged at 90° with respect to the irradiation direction R, receives diffuse radiation (in the diffusion direction D) from the gas bubbles present in the foam, without receiving any direct radiation from the source 101 .

[0119] Because the second photodiode 109 is positioned to capture only diffuse radiation, a very sensitive photodiode can be used, for example by using a very high gain amplifier associated with the photodiode itself, so as to be able to detect the passage of even a single small bubble.

[0120] The fact of having two orthogonally arranged photodiodes 105 and 109 and capturing mutually orthogonal portions 107 and 111 of the radiation 103 allows to achieve a foam sensor 100 with a very wide measuring range before saturating the electrical signals generated by the two photodiodes 105 and 109 .

[0121] Advantageously, in case the radiation source comprises a laser source, and therefore in case the radiation 103 consists of a laser beam, the first photodiode 105 may also be sensitive to the modulation of the laser beam power due to the effect of the so-called “self-mixing interferometry”. By analyzing the so-called “self-mixing” signal of the first photodiode 105, the presence of even very small gas bubbles (which would not otherwise produce a shadow) may be detected, so that they could otherwise be detected by the first photodiode 105 itself.

[0122] It has been noted from experimental testing of the foam sensor 100 that the amplitude of the variation of the voltage signal generated by the photodiodes 105 and 109 depends on the number and size of the bubbles passing at the photodiodes themselves and therefore substantially on the quality of the foam.

[0123] For example, starting from calculating the RMS value of the voltage signal generated by the first photodiode 105 and / or the second photodiode 109, the size of the bubbles and their approximate number can be estimated.

[0124] Advantageously, more complex signal processing may be performed, such as a non-linear function capable of taking into account the magnitude of the shadow (related to the first photodiode 105) or the degree of diffusion (related to the second photodiode 109) based on the volume of the bubble.

[0125] For example, the frequency spectrum of the signal generated by the photodiodes 105 and / or 109 may also be processed to obtain parameters indicative of the quality of the foam.

[0126] The foam sensor 100 is not only able to detect the passage of air bubbles, but also the passage of various types of particles that may be present in the foam, such as, for example, pollutants or microplastic particles.

[0127] Furthermore, the foam sensor 100 can also distinguish the freshness of the milk used to produce the foam. In fact, the foam sensor 100 can detect the aggregation of micelles present in milk that is no longer fresh or expired, which leads to anomalies in the signals generated by the first photodiode 105 and / or the second photodiode 109.

[0128] In fact, during the passage of the bubble, the refractive index of the radiation changes depending on the subsequent crossing of the liquid-gas interface and the gas-liquid interface, which causes the photodiode 105 and / or 109 to generate an electrical signal that is different from the electrical signal generated when a particle passes, because of the different changes in the refractive index caused by the crossing of the liquid-solid interface and the solid-liquid interface, and because the solid particles may be opaque and therefore further attenuate the radiation and exhibit different diffusion.

[0129] The foam sensor 100 is also able to distinguish the passage of liquids other than milk, such as, for example, cleaning liquids that may be used in a cleaning cycle of the device 1 for producing foam.

[0130] Therefore, the two phenomena can be distinguished by analyzing the signals generated by photodiodes 105 and / or 109 .

[0131] Advantageously, the signal 106 generated by the first photodiode 105 may be suitably processed, for example by autocorrelation, to estimate the size of the bubble passing in front of the photodiode itself.

[0132] In fact, the bubble acts as a kind of lens for the radiation 103 that strikes it, leaving a kind of imprint on the photodiode 105 .

[0133] In particular, in the case of a larger bubble, the radiation 103 is deflected by the edges of the bubble itself (which thus shields the photodiode 105 ), but passes through the center of the bubble, thereby reaching the photodiode 105 .

[0134] The size of the bubble passing in front of the photodiode 105 can thereby be indirectly measured using an algorithm that is able to distinguish and recognize the specific pattern of alternation of light and shadow.

[0135] Advantageously, the foam sensor 100 may comprise one or more additional photodiodes placed laterally to the first photodiode 105 in a direction parallel to the flow direction S of the foam in the duct 7 , said photodiodes being arranged to detect in any case the radiation 103 emitted by the radiation source 101 .

[0136] Thus, since the distance between the photodiodes placed in this direction is known, the cross-correlation over time of the signals detected by said photodiodes allows to precisely identify identical events over time, such as for example the passage of a bubble, and thus to obtain the flow velocity of the foam inside the duct 7 .

[0137] The presence of further photodiodes located to the sides of the first photodiode 105 and the second photodiode 109 in a direction parallel to the flow direction S advantageously allows for a more precise and robust measurement.

[0138] The present invention also relates to a method for estimating the mass of foam obtained by mixing liquid with air or other gases by means of a foam sensor 100 as described above, and a method for estimating the mass of foam obtained by mixing liquid with air or other gases in a device for generating foam of liquid as described above.

[0139] According to the invention, the method comprises at least a step of detecting a first electrical signal 106 generated by a first photodiode 105 and / or a second electrical signal 110 generated by a second photodiode 109, and a step of processing said first electrical signal 106 and / or said second electrical signal 110 to obtain measured values ​​of the number and size of bubbles present in the foam volume, in particular in the foam volume flowing through the conduit 7, during a given period of time.

[0140] Advantageously, the above method may also comprise a step of calculating a probability density function (PDF) of the distribution of the bubbles, said probability density function being a function of the size of the bubbles themselves, for example of their diameter. In this way, an indication of the degree of stability of the foam may be obtained. In fact, smaller bubbles tend to coalesce with larger ones, thus favouring the dispersion of the gas trapped in the bubbles. Conversely, the uniform presence of small bubbles confers greater stability to the foam and therefore allows it to persist for a while in the cup.

[0141] Advantageously, the foam sensor 100 thus allows monitoring the stability of a foamed drink, since the PDF of the distribution of bubbles can be monitored.

[0142] As mentioned above, the present invention also relates to a method for monitoring a cleaning cycle of a device for generating foam of a liquid, comprising the following steps:

[0143] - circulating the cleaning liquid in the device (1) itself;

[0144] - detecting a first electrical signal 106 generated by the first photodiode 105 and / or a second electrical signal 110 generated by the second photodiode 109;

[0145] - processing the first electrical signal 106 and / or the second electrical signal 110 to obtain a signal indicating the passage of milk or washing liquid, or a mixture of milk and said washing liquid;

[0146] - interrupting or continuing a circulation phase of the washing liquid on the basis of a signal indicating the passage of milk or washing liquid, or a mixture of milk and said washing liquid.

[0147] Advantageously, in fact, the cleaning cycle can be interrupted when the signal indicates that only cleaning liquid has passed, which means that milk residues that may be present in the device 1 have been cleaned.

[0148] In practice, it has been found that the device for generating foam and the associated foam sensor according to the invention achieve the intended task and objects, since they allow detecting quality properties of the foam in a simple, robust and economical manner.

[0149] Another advantage of the device for producing foam according to the invention is that the associated foam sensor is able to monitor the properties of the foam directly at the moment of its delivery, ie when it is added to the coffee to form the finished product.

[0150] Yet another advantage of the device for generating foam according to the invention is that, thanks to the presence of the foam sensor, it is possible to perform an automatic online calibration of the device itself, without the need to resort to external equipment.

[0151] A further advantage of the device for producing foam according to the invention lies in the fact that the properties of the produced foam can be adjusted and varied so as to remain constant even when external conditions change (e.g. temperature changes, changes in properties of the raw materials, wear of device components).

[0152] The characteristics of the foam that can be adjusted and varied include, for example: the number and size of air bubbles, the temperature of the foam, the hardness of the foam, the texture of the foam, the fluidity and creaminess aspects of the foam, the stability of the foam, uniformity, brightness, and the melt-in-the-mouth sensation.

[0153] A further advantage of the device for generating foam according to the invention is that the properties of the foam generated also during a single delivery can be varied and adjusted.

[0154] Indeed, not all of the milk added to the coffee to form a cappuccino, for example, has to be in the form of foam, and in fact it is preferred that part of the milk is added to the coffee in the general liquid phase and part of the milk is added to the coffee in the form of foam.

[0155] A further advantage of the invention is that the foam sensor does not need to be in direct contact with the liquid, since it is sufficient for it to pass through an at least partially transparent conduit.

[0156] Yet another advantage of the foam sensor according to the present invention is that it has no moving parts which could tend to degrade the performance of the sensor over time.

[0157] Yet another advantage lies in the fact that the foam sensor is absolutely cheap and can therefore be used on a large scale in any type of application and environment, since it essentially consists of a low-cost and mass-consumable diode or photodiode.

[0158] A further advantage lies in the fact that the foam sensor has a good sensitivity and a very high response speed.

[0159] Yet another advantage of the foam sensor according to the invention lies in the fact that it also detects the presence of contaminant particles in the drink.

[0160] A further advantage of the foam sensor according to the present invention is the detection of the volume of the delivered substance in the cup, since it is able to detect the velocity and flow rate of the delivered liquid phase and foam phase.

[0161] The device for foam generation of liquids and the foam sensor conceived thereby are susceptible of numerous modifications and variations, all of which are within the scope of the inventive concept.

[0162] Moreover, all the details may be replaced by other technically equivalent elements.

[0163] In practice, any materials may be used as desired, provided they are compatible with the specific use, dimensions and possible shapes.

Claims

1. A device (1) for producing foam of a liquid, the device comprising: - a liquid source (13), wherein the liquid is one of milk and coffee, - a source of air (11) or other gas, - a mixing device (3) in fluid communication with the liquid source (13) and the air source (11), adapted to mix liquid from the liquid source (13) with air from the air source (11) to produce foam of the liquid, wherein the mixing device comprises a pump adapted to draw the liquid from the liquid source and to draw the air from the air source, thereby mixing the drawn liquid and air to produce foam, or the mixing device comprises an agitator member configured to agitate the liquid to achieve incorporation of air or gas to produce foam, a conduit (7) in fluid communication with the mixing device (3) downstream of the mixing device (3), the foam flowing along the conduit (7) in a flow direction (S), wherein the device comprises a foam sensor (100) associated with the conduit (7), the foam sensor (100) comprising a radiation source (101) suitable for generating radiation (103) irradiating the conduit (7) along an irradiation direction (R) incident on the flow direction (S), wherein a first part of the radiation passes through the foam and a second part of the radiation is diffused by the foam, The foam sensor (100) further comprises: a first photodiode (105) arranged in the irradiation direction (R) from a side opposite to the radiation source (101) with respect to the conduit (7), the first photodiode (105) generating a first electrical signal (106) in response to the passage of the radiation through the first portion of the foam flowing along the conduit (7), or a second photodiode (109) arranged along a diffusion direction (D) perpendicular to the irradiation direction (R), the second photodiode (109) generating a second electrical signal (110) as a function of the second portion of the radiation diffused by the foam along the diffusion direction (D), The first electrical signal (106) and / or the second electrical signal (110) are processed to obtain measurement data of the number and size of bubbles of foam passing in front of the first photodiode (105) and / or in front of the second photodiode (109).

2. The device (1) for producing foam of a liquid according to claim 1, characterized in that The foam sensor (100) includes both the first photodiode (105) and the second photodiode (109).

3. The device (1) for producing foam of a liquid according to claim 1 or 2, characterized in that The device comprises a processing and control unit (15) connected to the foam sensor (100) so as to receive and process the first electrical signal (106) generated by the first photodiode (105) and / or the second electrical signal (110) generated by the second photodiode (109), the processing and control unit (15) being configured to regulate the actuation of the mixing device (3) based on the first electrical signal (106) and / or the second electrical signal (110).

4. The device (1) for producing foam of a liquid according to claim 3, characterized in that The device comprises a proportional valve (17) associated with the air source (11) and connected to the processing and control unit (15), the processing and control unit (15) being configured to operate the proportional valve (17) so as to adjust the flow rate of air from the air source (11) based on the first electrical signal (106) and / or the second electrical signal (110).

5. Device (1) for producing foam of a liquid according to the preceding claim 3, characterized in that The foam sensor (100) comprises a housing (113) which is penetrated by the conduit (7) and houses the radiation source (101), the first photodiode (105), the second photodiode (109) and the processing and control unit (15).

6. The device (1) for producing foam of a liquid according to claim 1 or 2, characterized in that The radiation source (101) comprises a laser source, the radiation (103) comprises a laser beam, and the first photodiode (105) detects modulation of the power of the laser beam caused by a back-injection interference effect.

7. The device (1) for producing foam of a liquid according to claim 1 or 2, characterized in that The conduit (7) comprises, downstream of the mixing device (3) and upstream of the foam sensor (100), a portion (8) configured to generate a distributed pressure drop of the foam.

8. The device (1) for producing foam of a liquid according to claim 3, characterized in that The device comprises a heating device (21) for the foam and / or the liquid, the heating device (21) being connected to the processing and control unit (15), the processing and control unit (15) being configured to regulate the temperature of the foam and / or the liquid by means of the heating device (21).

9. The device (1) for producing foam of a liquid according to claim 3, characterized in that The device comprises a temperature sensor (23) connected to the processing and control unit (15).

10. The device (1) for producing foam of a liquid according to claim 3, characterized in that The processing and control unit (15) is configured to sample the electrical signal generated by the first photodiode (105) and / or by the second photodiode (109) at a frequency greater than 8 KHz.

11. A method for monitoring a cleaning cycle of a device (1) for generating foam of a liquid according to any one of the preceding claims 1 to 10, comprising the following steps: - circulating a cleaning liquid in the device (1); - detecting the first electrical signal (106) and / or the second electrical signal (110); - processing the first electrical signal (106) and / or the second electrical signal (110) to obtain a signal indicating the passage of milk or the washing liquid, or the passage of a mixture of milk and the washing liquid; - interrupting or continuing the phase of circulating the washing liquid in the device (1) on the basis of this signal indicating the passage of milk or washing liquid, or of a mixture of milk and said washing liquid.

12. A foam sensor (100) adapted to be associated with a conduit (7) in which a foam obtained by mixing a liquid with air or another gas flows along a flow direction (S), wherein the liquid is one of milk and coffee, wherein the foam sensor (100) comprises a radiation source (101) adapted to generate radiation (103) irradiating the conduit (7) along an irradiation direction (R) incident on the flow direction (S), and wherein a first part of the radiation passes through the foam and a second part of the radiation is diffused by the foam, The foam sensor (100) further comprises: a first photodiode (105) arranged in the irradiation direction (R) from a side opposite to the radiation source (101) with respect to the conduit (7), the first photodiode (105) generating a first electrical signal (106) in response to the passage of the radiation through the first portion of the foam flowing along the conduit (7), or a second photodiode (109) arranged along a diffusion direction (D) perpendicular to the irradiation direction (R), the second photodiode (109) generating a second electrical signal (110) as a function of the second portion of the radiation diffused by the foam along the diffusion direction (D), The first electrical signal (106) and / or the second electrical signal (110) are processed to obtain measurement data of the number and size of bubbles of foam passing in front of the first photodiode (105) and / or in front of the second photodiode (109).

13. The foam sensor (100) according to claim 12, characterized in that: The foam sensor (100) includes both the first photodiode (105) and the second photodiode (109).

14. The foam sensor (100) according to claim 12 or 13, characterized in that: The foam sensor is associated with a duct (7) of a device (1) for generating foam of a liquid according to any one of claims 1 to 10.

15. A method for estimating the quality of foam obtained by mixing a liquid with air or other gas by means of a foam sensor (100) according to claim 12, characterized in that The method comprises the following steps: - detecting the first electrical signal (106) and / or the second electrical signal (110); - Processing the first electrical signal (106) and / or the second electrical signal (110) to obtain measurement data of the number and size of bubbles of the foam passing in front of the first photodiode (105) and / or in front of the second photodiode (109).

16. A method for estimating the quality of foam obtained by mixing a liquid with air or another gas by means of a foam sensor (100) according to claim 15, characterized in that The method comprises the step of calculating a probability density function of the distribution of bubbles as a function of the size of the bubbles.

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