Beverage Preparation Machine

Abstract

The nozzle 20 has a fluid passage 26 that defines a fluid flow path from the inlet end of the passage to the outlet end of the passage. The restrictor 29a is movable relative to the passage under the control of an actuator system 27 to vary the minimum cross-sectional area of ​​the fluid flow path through the passage. The restrictor 29a can be moved to protrude into the passage, providing a restricted opening, or removed from the passage, allowing unrestricted flow through the passage. The nozzle 20 is particularly suited for use in beverage preparation machines to produce microfoam in beverages. Retracting the restrictor 29 from the passage 26 allows the passage and the restrictor to be cleaned by flushing the nozzle. The restrictor 29 can be a pin-like member aligned with the passage and movable parallel to the axis of the passage.

Description

[Technical Field]

[0001] The present invention ,of This invention relates to a beverage preparation machine equipped with a slur. [Background technology]

[0002] Beverages containing microfoam, especially milk coffee drinks, are becoming increasingly popular. The crema on coffee is also a form of microfoam. It is known to use nozzles with small cross-sectional flow areas in beverage preparation machines, such as coffee machines, to create microfoam in beverages. For example, nozzles with circular flow paths less than 1 mm in diameter through which the beverage flows have been found to be very effective in frothing coffee and milk. A problem with known nozzle arrangements is that they tend to clog over time and are difficult to clean or flush out. This often requires the intervention of a service engineer to resolve the issue.

[0003] There is therefore a need for an alternative nozzle that can be used in a beverage machine to produce foam in a beverage that overcomes, or at least mitigates, some or all of the drawbacks of known nozzles.

[0004] In particular, there is a need for an alternative foam generating nozzle that is easier to clean or flush than known foam generating nozzles.

[0005] There is also a need for a beverage preparation machine with an alternative nozzle that can be used to generate foam in a beverage that overcomes, or at least mitigates, some or all of the drawbacks of known machines.

[0006] In particular, there is a need for alternative beverage preparation machines having foam generating nozzles that are easier to clean or flush than known foam generating nozzles. Summary of the Invention [Problem to be solved by the invention]

[0007] Aspects of the present invention relate to a nozzle, in particular a nozzle for producing foam in a beverage, and to a beverage preparation machine.

[0008] According to a first aspect of the present invention, there is provided a nozzle having a fluid flow passage defining a fluid flow path from an inlet end of the passage to an outlet end of the passage, the nozzle having a restrictor movable relative to the fluid passage to vary a minimum cross-sectional area of ​​the fluid flow path through the fluid passage, and the nozzle having an actuator arrangement for moving the restrictor.

[0009] In the nozzle according to the first aspect of the invention, the restrictor can be moved to reduce the minimum cross-sectional area of ​​the flow path to provide a restricted opening for use such as when producing foam in a beverage, and can be moved to increase the minimum cross-sectional area of ​​the flow path to allow the nozzle to be cleaned by flushing, or when foam production is not required.

[0010] In one embodiment, the restrictor is movable to at least one retracted position in which it is fully withdrawn from the passageway.

[0011] In one embodiment, the restrictor is movable to at least one advanced position in which the restrictor protrudes into the passageway. The restrictor is movable to any one of a range of different advanced positions in which the restrictor protrudes into the passageway by different amounts. When the restrictor protrudes into the passageway, at least a portion of the fluid flow path through the passageway can be defined by a gap between the restrictor and a surface of the passageway.

[0012] In one embodiment, the passage has a longitudinal axis, the restrictor is elongated and has a longitudinal axis parallel to or coaxial with the axis of the passage, and the restrictor has a cross-sectional area that is smaller than the cross-sectional area of ​​the passage. The restrictor and the passage may have the same shape in cross section.

[0013] In one embodiment, the restrictor is an elongated pin-like member aligned parallel or coaxially with the axis of the passageway and reciprocally movable in a direction parallel to the axis.

[0014] The actuator arrangement may include a stepper motor.

[0015] In one embodiment, the nozzle comprises a body defining a bore having an axis, a passageway located in a region of the bore coaxial with the axis, the nozzle comprising an inlet port for directing fluid into the bore upstream of the passageway, a restrictor aligned parallel or coaxially with the bore and the passageway, and an actuator arrangement adapted to reciprocate the restrictor along the bore to move the restrictor in and out of the passageway. The passageway may be defined by an annular sleeve mounted within the bore or by a portion of the bore itself. The inlet port may be configured to direct fluid into the bore in a direction substantially perpendicular to the axis of the bore. The body may be a single, integral component or may be fabricated from several separate components. In one embodiment, the body may define the bores of two or more nozzles according to the first aspect of the present invention. The restrictor is an elongated pin-shaped member, and the nozzle is configured so that the pin-shaped member is positionable in at least one advanced position. In the advanced position, a portion of the pin-shaped member penetrates the passage while another portion of the pin-shaped member is positioned within the bore opposite the inlet port, allowing fluid entering the bore through the port to be directed toward the pin-shaped member and flow around the pin-shaped member to enter the passage. The pin-shaped member is positionable in at least one retracted position, in which the pin-shaped member is fully retracted from the passage so that it is fully positioned on the side of the inlet port opposite the sleeve. The actuator arrangement may include a reciprocating slidable actuator member in a further region of the bore extending beyond the inlet port opposite the sleeve. The actuator member may have a main body portion slidably positioned in the main bore, with the pin-shaped restrictor member protruding from an end of the main body facing the passage. A sealing arrangement may be provided to prevent fluid from flowing through the main body portion of the actuator member in the bore.

[0016] In one embodiment, the passage is cylindrical and at least a portion of the restrictor that protrudes into the passage is cylindrical but has a smaller outer diameter than the passage.

[0017] In one embodiment, the nozzle is part of a foam generating device of a beverage preparation machine.

[0018] According to a second aspect of the present invention, there is provided a nozzle having a fluid passageway. The fluid passageway defines a fluid flow path from an inlet end of the passageway to an outlet end of the passageway. The nozzle has a restrictor movable relative to the fluid passageway under the control of an actuation system to vary the minimum cross-sectional area of ​​the fluid flow path through the fluid passageway. The restrictor can be moved to protrude into the fluid passageway to provide a restricted opening to the fluid passageway, and moved to remove the restrictor from the fluid passageway to provide unrestricted flow through the fluid passageway. The restrictor can be a pin-like member aligned with the fluid passageway and movable parallel to the axis of the fluid passageway.

[0019] According to a third aspect of the present invention, there is provided a beverage preparation machine having an apparatus for generating foam on beverage ingredients, the foam generating apparatus comprising at least one nozzle according to either the first or second aspect of the present invention described above.

[0020] The foam generating device may have a plurality of nozzles according to either the first or second aspect of the present invention. In one embodiment, the foam generating device includes at least two of the nozzles fluidly connected or connectable in series or parallel. In one embodiment, the foam generating device includes four of the nozzles, a first pair of the nozzles fluidly connectable in series and a second pair of the nozzles fluidly connectable in series. The foam generating device may include at least one actuator operably connected to the restrictors of at least two of the nozzles to simultaneously move the restrictors of the at least two nozzles relative to their respective fluid passages. The actuator may be operably connected to the restrictors of all of the nozzles of the foam generating device. In one embodiment, each of the at least two nozzles includes a bore having an axis, the fluid passage is located within the bore and includes an inlet port for directing fluid into the bore upstream of the fluid passage, the restrictor is elongated and extends parallel or coaxially with the fluid passage, and the actuator arrangement is adapted to reciprocate the restrictor along the bore to move the restrictor in and out of the fluid passage. The bores of the at least two nozzles may be defined within a common body. DETAILED DESCRIPTION OF THE INVENTION

[0021] In order that the invention may be more clearly understood, one or more embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a schematic diagram illustrating a portion of a fluid flow system in an embodiment of a beverage preparation machine incorporating at least one nozzle according to an aspect of the present invention; [Figure 2] 1 is a semi-schematic longitudinal cross-sectional view through an embodiment of a nozzle according to an aspect of the present invention showing the nozzle in a foam-generating configuration; [Figure 3] 3 is a cross-sectional view of a portion of the nozzle of FIG. 2 taken along line AA. [Figure 4]FIG. 3 is a view similar to FIG. 2 but showing the nozzle in a non-foam generating configuration. [Figure 5] 5 is a cross-sectional view of a portion of the nozzle taken along line BB in FIG. 4. [Figure 6] The images on the left are cross-sectional views taken along line AA in FIG. 3, and the corresponding images on the right are cross-sectional views taken along line BB in FIG. 5, illustrating that a variety of different cross-sectional shapes can be used for the fluid passages and restrictors that form part of the nozzles of FIGS. 2-4. [Figure 7] 1 is a perspective view of a multi-channel foam generating device for use in a beverage preparation machine incorporating four foam generating nozzles according to one embodiment of the present invention, the body forming part of the device being made transparent to allow internal details to be seen; [Figure 8] 8 is a longitudinal cross-sectional view, with parts cut away, of the device of FIG. 7, showing the device in a foam-generating configuration. [Figure 9] 9 is a view similar to FIG. 8, but showing the device in a configuration that does not generate bubbles.

[0023] Embodiments of the present invention will now be described with reference to a nozzle forming part of a beverage preparation machine for producing foam or froth on a beverage. Nozzles according to the present invention can be used in machines for preparing a wide variety of beverages, both hot and cold, including but not limited to coffee (including espresso and milk coffee), milk (which may be flavored), chocolate, and tea.

[0024] FIG. 1 is a schematic diagram of a portion of a fluid flow path in one embodiment of a beverage preparation machine 1 having a foam generator 2 incorporating at least one nozzle according to the present invention. In this machine, a gas pump 3 selectively delivers gas 4 under pressure to a fluid line 5 via a valve 6 and a restriction 7. The gas 4 is mixed with liquid beverage ingredients 8 from a source (not shown), and a pump 9 operates to pump the gas / liquid mixture through a foam generator 2 that can be selectively used to generate foam in the gas / liquid mixture. From the foam generator 2, the mixture (which may or may not be foamed) is directed through an in-line heater 10 and then dispensed via a dispensing outlet 11 into a suitable container, such as a cup 12. A dump valve 13 is located in the fluid line between the heater 10 and the dispensing outlet 11. The dump valve 12 is selectively operable to divert fluid to a dump via a one-way valve 14.

[0025] In coffee-type beverage preparation machines, the gas 4 is typically air and is mixed with the liquid components of the beverage, such as water, coffee, milk, coffee / milk mixtures, chocolate milk, etc. However, nozzles according to the present invention can be configured for use with a wide variety of gas / liquid combinations and can be adapted for use in applications other than frothing beverage ingredients.

[0026] A first embodiment of a nozzle 20 according to one aspect of the present invention is shown schematically in Figures 2 to 5. One or more nozzles 20 of this type may be incorporated into a foam generating device 2 in a beverage preparation machine 1 as shown in Figure 1.

[0027] Nozzle 20 includes a body 21 defining an elongated cylindrical main bore 22 extending therethrough. The body defines an inlet port 23 partially along the length of the main bore, having an inlet channel 24 opening into bore 22. Inlet port 23 is in the form of a cylindrical stepped bore, the axis of which is at substantially 90 degrees to the axis of the main bore. Inlet port 23 is in fluid connection with a source of the gas and liquid mixture to be foamed, such as fluid line 5 and pump 9 of the machine of FIG. 1.

[0028] The main bore 22 has a generally central region 22a into which the inlet port 23 is inserted, a second region 22b, which may be referred to as the actuator region to the left of the inlet port as shown, and a third region 22c, which may be referred to as the flow region to the right of the inlet port as shown.

[0029] A cylindrical annular pipe or sleeve 25 is located in the third region 22c of the main bore. The sleeve 25 fits snugly within the main bore 22c, preventing fluid from flowing between the exterior of the sleeve and the surface of the main bore. Alternatively, a sealing arrangement can be used to prevent fluid from flowing between the exterior of the sleeve and the surface of the main bore. A central passageway 26 in the sleeve 25 defines a flow path from an inlet end 26a of the passageway adjacent the inlet port 23 to an opposite outlet end 26b. The outlet end of the passageway 26 is fluidly connected to the outlet 11 of the beverage preparation machine, through which the prepared beverage is dispensed into a suitable container, such as a cup 12. In an alternative embodiment, the passageway 26 is formed directly within the body 21.

[0030] A cylindrical actuator member 27 is slidably positioned within the second region 22b of the main bore. The actuator member 27 has a main body portion 28 that fits snugly within the main bore 22b and an elongated pin-like portion 29 of reduced diameter at the end facing the sleeve. The pin-like portion 29 is cylindrical and coaxially aligned with the passageway 26 through the sleeve 25. The pin-like member has an outer diameter slightly smaller than the inner diameter of the sleeve 25 so that it can be inserted into the passageway with little clearance. This pin-like portion 29 is referred to as the restrictor.

[0031] The actuator member 27 is operably connected to an actuator (30, FIG. 7) configured to slide the actuator member 27 back and forth within the main bore 22b, as indicated by arrow 31, between an advanced or foam-producing position shown in FIGS. 2 and 3 and a retracted or non-foam-producing position shown in FIGS. 4 and 5. The actuator 30 in this embodiment is a stepper motor, although any suitable actuator capable of linearly reciprocating the actuator member 27 along the bore may be used. Other suitable types of actuators include, for example, linear electronic or fluid-powered actuators. A seal (32, FIG. 8) is located around the exterior of the main body portion 28 of the actuator member 27 adjacent its inner end. The seal 32 engages the surface of the main bore 22b to prevent fluid from flowing past the seal 32 between the main body portion 28 of the actuator member 27 and the surface of the main bore 22b.

[0032] 2 and 3, when the actuator member 27 is in the advanced or foam-generating position, the free end region 29a of the pin-shaped restrictor 29 protrudes into the passageway 26 of the sleeve 20. The restrictor 29 has an outer diameter slightly smaller than the inner diameter of the sleeve 25, such that a small annular gap 33 exists between the restrictor 29 and the inner surface 34 of the sleeve 25, through which fluid can flow. A portion of the restrictor 29b near the main body portion remains outside the sleeve, but is located within the central region 22a of the main bore 22 opposite the inlet port 23. In use, a gas / liquid mixture flows under pressure through the inlet port 23, where it encounters the exposed portion of the restrictor 29b, then flows through the narrow annular section 33 between the restrictor 29 and the sleeve 25, along the remainder of the passageway 26 toward the outlet. As the gas / liquid mixture enters main bore 22, it strikes restrictor 29b and passes through narrow annulus 33, which acts as a constricted nozzle, generating foam in the gas / liquid mixture. By varying the amount that restrictor 29 penetrates along passageway 26, the degree of restriction can be adjusted to vary the foam-generating characteristics. Generally, the further restrictor 29 protrudes into passageway 26, the greater the restriction in the flow path and the more foam will be generated. The shorter the distance that restrictor 29 protrudes into the passageway, the less restriction there is and the less foam will be generated. Thus, actuator 30 can be controlled to move actuator member 27 to a variety of different advanced, or foam-generating, positions according to a predetermined algorithm to generate a desired amount of foam for any given gas / liquid mixture.

[0033] When the actuator member 27 is in its retracted, non-foaming position, as shown in FIGS. 3 and 4 , the restrictor 29 does not protrude into the passageway 26 and can, in fact, be located within the second region 22b of the main bore 22a, such that the restrictor 29 is located entirely within the main bore on the opposite side of the inlet port 23 from the sleeve 22. In this position, the restrictor does not impede flow through the inlet port 23 and the passageway 26. The actuator member 27 can be moved to the retracted position to dispense a still beverage product through the nozzle. In this case, the liquid beverage product does not need to be mixed with gas before passing through the nozzle. Furthermore, with the actuator member 27 and the restrictor 29 in the retracted position, the interior of the restrictor 29 and the sleeve 25 can be flushed and cleaned. For this purpose, a liquid (which may be warm water or may contain cleaning chemicals, such as a descaling compound) is introduced into the main bore 22 through the inlet port 23. The liquid can flow around the restrictor 29 exposed in the main bore and pass unimpeded through the passageway 26. This can be performed as part of a cleaning protocol according to a predetermined algorithm under the control of the beverage preparation machine's electronic control system or under manual control of the user, such as selection of a cleaning function via a user interface.

[0034] Nozzles 20 according to the present invention allow for the cross-sectional area and length of the restricted opening through the nozzle to be varied, and therefore may be referred to as variable aperture or variable restriction nozzles.

[0035] In testing, it has been found that satisfactory foam generation is achieved using a sleeve 25 having a passageway 26 with a diameter of 2 mm and a restrictor 29 with an outer diameter in the range of 1.75 mm to 1.95 mm. This results in a restrictor 29 protruding into the passageway 26 of approximately 0.74 mm. 2 ~0.16mm 2This creates an annular gap 33 having an effective cross-sectional area in the range of 0.97 mm to 0.44 mm. This is equivalent to a fixed circular nozzle opening having a diameter in the range of approximately 0.97 mm to 0.44 mm. It has been found that the restrictor 29 may need to protrude into the passageway by 1 to 2 mm to produce satisfactory microfoam. However, with a nozzle of the above dimensions, the restrictor 29 can protrude into the passageway 26 by any amount from 0.5 mm to 6 mm or more when in the foam-generating configuration. It will be understood that the above dimensions are merely exemplary and may vary. For example, the diameter of the passageway 26 may be greater or less than 2 mm, and the diameter of the restrictor 29 may be varied accordingly to provide a restricted passageway 33 of the desired cross-sectional area. One skilled in the art would have no difficulty in establishing appropriate dimensions for any given application by trial and error. However, generally, the cross-sectional area of ​​the restricted annular portion 33 of the flow path through the passageway is approximately 0.79 mm. 2 and more preferably less than 0.2 mm to produce microfoam in the beverage. 2 ~0.6mm 2 is expected to be in the range of

[0036] In this embodiment, the passage 26 is cylindrical, and the restrictor 29 is also cylindrical and coaxial with the passage. However, this is not required, and the passage 26 and the restrictor 29 can have different shapes as long as the restrictor 29 can be introduced into the passage 26 to create a constricted flow path for foam generation. For example, as shown in FIG. 6 , in cross section, the passage 26 and the restrictor 29 can be, for example, oval, square, or rectangular, star-shaped with any given number of points, cross-shaped with any suitable variation in width / depth, parallelogram, teardrop, pentagon, or any type of polygon. They may also be irregularly shaped. The passage 26 and the restrictor 29 may have the same cross-sectional shape, but this is not required. For example, the passage 26 may be circular in cross section, while the restrictor 29 has another cross-sectional shape, such as a star or polygon. Furthermore, it is not required that the restrictor be coaxial with the passage 26; the axis of the restrictor 29 may be offset from the axis of the passage 26. The cross-sectional shape of the restrictor 19 may also vary along its length, at least in the region 29a that penetrates the passageway 26.

[0037] 7-9 illustrate one embodiment of a multi-channel foam generating device 2 for use with a beverage preparation machine 1 such as that shown in FIG. 1. The device 2 incorporates multiple variable-throttle nozzles 20 similar to those described above. In this embodiment, the device incorporates four nozzles 20a-20d, although the number of nozzles can be varied as needed. Each nozzle defines a flow path through which a beverage product ingredient can be routed. Each beverage product ingredient is typically a gas / liquid mixture from which foam is generated, but may also be a liquid from which foam is not generated. Not all nozzles need be used simultaneously. Two or more of the nozzles may be used for different beverage product ingredients that may be combined downstream. It is also possible to use two or more nozzles for the same beverage product ingredient. In this case, the nozzles may be connected in parallel. This is advantageous when dispensing a larger flow rate of the ingredient than can be passed through a single nozzle. If a beverage product ingredient is particularly difficult to froth, two or more nozzles may be connected in series so that the ingredient passes through the nozzles in succession.

[0038] Each of the nozzles 20a-20d of the device 2 is essentially similar to that described above with respect to Figures 2-5, having a main bore 22, an inlet port 23, a sleeve 25 defining an inner passageway 26, and an actuator member 27 having a main body portion 28 carrying a restrictor 29. In this embodiment, all of the main bores 22 are defined within a single common body 21 extending parallel to one another through the body. The main bores 22 are arranged in an array including two rows and two columns, with each row and each column containing two of the main bores. While it may be preferable to provide a bore 22 for all of the nozzles in a single body 21, this is not necessary. Each main bore 22 can be provided in a separate body 21, or there may be two or more bodies 21, each defining one or more main bores 22, depending on the number of nozzles required and packaging and manufacturing considerations.

[0039] In this embodiment, the actuator members 27 of all four nozzles 20a-20d are operatively connected to a single actuator in the form of a stepper motor 30, which moves all of the actuator members 27 simultaneously, either all forward or all backward. As shown, the actuator members are all connected to an actuator plate 35 that is moved by the stepper motor 30. However, in alternative embodiments, multiple actuators may be provided, each actuator operatively connected to one or more of the actuator members. Figure 8 shows a pair of nozzles 22a, 22b with the actuator members 27 in an advanced, foam-generating position, while Figure 9 shows the actuator members 27 in a retracted, non-foam-generating position. Fluid flow through the nozzles is indicated by arrows. Each of the nozzles 20a-20d has an outlet port 36 at the downstream end of its main bore for directing beverage ingredients out of the nozzle.

[0040] For use in the beverage preparation machine of FIG. 1 , the outlet ports can be fluidly connected to the in-line heater 10 and the outlet port 11, respectively. However, if the gas / liquid mixture needs to be passed through more than one nozzle to generate the required microfoam, the nozzles can be connected in series, with the outlet port of one nozzle connected to the inlet port of another nozzle. This can be a permanent fluid connection, or a valve arrangement can be provided to allow the nozzles to be selectively connected in series when required. In the embodiment of FIGS. 7-9 having four nozzles 22a-22d, the nozzles can be arranged in two pairs, with the nozzles of each pair connected in series. This allows each pair of nozzles to be used to generate foam (particularly microfoam) for different beverage ingredients. For example, one pair of nozzles 22a, 22b can be connected in series and used to generate foam for an air-coffee mixture, while the other pair of nozzles 22c, 22d can be connected in series and used to generate foam for an air-milk mixture. The two pairs of nozzles may operate simultaneously to froth and then mix the beverage ingredients, or they may be used at different times to produce different beverages, either alone or mixed with other beverage ingredients.

[0041] The embodiments are described above by way of example only. Many variations are possible without departing from the scope of protection afforded by the appended claims. It should be understood that a variable aperture / restriction nozzle according to the present invention can be utilized in many different types of beverage preparation machines and is not limited to use in a machine such as that shown in FIG. 1 . For example, the beverage preparation machine need not use an in-line heater 10 downstream of the foam generation device 2. Rather, at least the liquid components of the beverage ingredients can be heated before entering the foam generation device 2, e.g., by a boiler. Indeed, while a variable aperture / restriction nozzle according to one aspect of the present invention is particularly suited to generating foam in a beverage preparation machine, a nozzle according to the present invention can be configured for use in other applications in which it is desirable to provide a restriction in the fluid flow path that can be altered or removed, either to modify the restrictor effect or to facilitate cleaning.

Claims

1. 1. A beverage preparation machine having a foam generating device for generating foam on beverage ingredients, comprising: the foam generating device comprising at least one nozzle having a fluid passageway defining a fluid flow path from an inlet end of the fluid passageway toward an outlet end of the fluid passageway; the nozzle having a restrictor movable relative to the fluid passage to vary a minimum cross-sectional area of ​​the fluid flow path through the fluid passage, the nozzle having an actuator arrangement for moving the restrictor; A beverage preparation machine, wherein the fluid passage has a longitudinal axis, and the restrictor is coaxial with or parallel to the fluid passage, the restrictor having a cross-sectional area smaller than the cross-sectional area of ​​the fluid passage.

2. The beverage preparation machine of claim 1 , wherein the restrictor is movable to at least one retracted position fully withdrawn from the fluid passage.

3. 3. A beverage preparation machine as claimed in claim 1 or claim 2, wherein the restrictor is movable to at least one advanced position in which the restrictor projects into the fluid passage.

4. 4. The beverage preparation machine of claim 3, wherein the restrictor is movable to any one of a range of different forward positions.

5. 5. The beverage preparation machine of claim 1, wherein when the restrictor protrudes into the fluid passage, at least a portion of the fluid flow path through the fluid passage is defined by a gap between the restrictor and a surface of the fluid passage.

6. A beverage preparation machine according to any preceding claim, wherein the restrictor and the fluid passage have the same shape in cross section.

7. The beverage preparation machine according to any one of claims 1 to 6, wherein the restrictor is an elongated pin-shaped member aligned parallel to or coaxial with the axis of the fluid passage and capable of reciprocating movement in a direction parallel to the axis.

8. A beverage preparation machine according to any preceding claim, wherein the actuator arrangement comprises a stepper motor.

9. 9. A beverage preparation machine as claimed in any preceding claim, wherein the nozzle comprises a body defining a bore having an axis, the fluid passage being located in the region of the bore such that it extends parallel or coaxially to the axis, the nozzle comprising an inlet port for directing fluid into the bore upstream of the fluid passage, the restrictor being aligned parallel or coaxially with the fluid passage, and the actuator arrangement adapted to reciprocate the restrictor along the bore to move the restrictor into and out of the fluid passage.

10. 10. The beverage preparation machine of claim 9, wherein the fluid passage is defined by an annular sleeve mounted in the region of the bore.

11. 11. The beverage preparation machine of claim 10, wherein the restrictor is an elongated pin-shaped member, and the nozzle is configured such that the pin-shaped member is positionable in at least one advanced position, and in the advanced position, when a portion of the pin-shaped member penetrates the fluid passage, another portion of the pin-shaped member is located within the bore opposite the inlet port, so that fluid entering the bore through the inlet port is directed towards the pin-shaped member and can enter the fluid passage by flowing around the pin-shaped member.

12. 12. The beverage preparation machine of claim 11, wherein the pin-shaped member is positionable in at least one retracted position, in which the pin-shaped member is fully withdrawn from the fluid passage so as to be fully positioned on the opposite side of the inlet port from the annular sleeve.

13. 13. A beverage preparation machine as claimed in any one of claims 10 to 12, wherein the actuator arrangement includes a reciprocally slidable actuator member in a further region of the bore extending beyond the inlet port opposite the annular sleeve.

14. 14. A beverage preparation machine as claimed in any preceding claim, wherein the fluid passage is cylindrical and at least a part of the restrictor that protrudes into the fluid passage is cylindrical but has a smaller outer diameter than the fluid passage.

15. A beverage preparation machine according to any preceding claim, wherein the foam generating device comprises a plurality of nozzles.

16. 16. The beverage preparation machine of claim 15, wherein the foam generating device comprises at least two of the nozzles connected in series or in parallel.

17. 17. The beverage preparation machine of claim 16, wherein the foam generating device comprises four of the nozzles, a first pair of the nozzles being fluidly connectable in series and a second pair of the nozzles being fluidly connectable in series.

18. 18. The beverage preparation machine of claim 16 or 17, wherein the foam generating device includes an actuator operatively connected to the restrictors of the at least two of the nozzles for simultaneously moving the restrictors of the at least two nozzles relative to their respective passages.

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