Milk-frothing device with dynamic mixing unit, and beverage maker containing the same

Abstract

The invention relates to a milk-frothing device with a dynamic mixing unit having a stator and a rotor which can be set in rotation relative to the stator, rotor and stator being configured such that milk and air can be conducted firstly to the dynamic mixing unit, subsequently, for frothing-up in the dynamic mixing unit, can be subjected multiple times to a shearing effect by rotation of the rotor relative to the stator and finally can be discharged out of the dynamic mixing unit.

Claims

1. A milk-frothing device, comprising: a dynamic mixing unit having a stator, the stator having a series of shearing elements, the dynamic mixing unit having a rotor that is rotatable relative to the stator, the rotor having a series of shearing elements that engage intermittently with the shearing elements of the stator, the rotor and the stator being configured to: conduct milk and air to the dynamic mixing unit, froth the milk and the air in the dynamic mixing unit, subject the frothed milk and air multiple times to a shearing effect caused by rotation of the rotor relative to the stator such that rotation of the rotor relative to the stator is configured to shear and change direction of milk and air flowing between one series of shearing elements of the rotor and a directly adjacent series of shearing elements of the stator, and discharge the frothed and sheared milk and air out of the dynamic mixing unit.

2. The milk-frothing device according to claim 1, wherein the rotor and the stator are further configured to: subject the frothed milk and air multiple times to the shearing effect when the frothed milk and air flow from an outer circumference of the rotor to a center of the rotor by rotation of the rotor relative to the stator.

3. The milk-frothing device according to claim 1, wherein the rotor is surrounded on its outer circumference side by the stator and by a housing which houses the rotor and is stationary relative to the stator; and wherein the rotor and the stator are configured to: conduct the milk and the air to a rear-side of the rotor, direct the milk and the air from the rear-side of the rotor, via centrifugal forces effected by rotation of the rotor, towards the outer circumference of the rotor, direct the milk and the air are from the outer circumference of the rotor, by the stator and/or of the housing and also flowing past the outer circumference of the rotor, towards a front-side of the rotor, subject the milk and the air to the multiple shearing effect when flowing from the outer circumference of the rotor to the center of the rotor by the rotation of the rotor, and discharge the milk and the air are out of the dynamic mixing unit.

4. The milk-frothing device according to claim 1, wherein the rotor and the stator, viewed radially outwards from an axis of rotation of the rotor, have respectively the series of shearing elements which are configured radially at a spacing from each other and with respectively a plurality of shearing elements, the rotor and the stator being positioned relative to each other such that, viewed along the axis of rotation, the shearing elements of the rotor and overlap with the shearing elements of the stator at least in portions and such that, viewed from the axis of rotation radially outwards, the series of shearing elements of the rotor alternate with the series of shearing elements of the stator.

5. The milk-frothing device according to claim 4, wherein for the series of shearing elements of the rotor and the series of shearing elements of the stator, which is directly adjacent radially thereto, and for all such pairs of radially directly adjacent series of shearing elements of the rotor and of the stator, through-openings for milk and air, which are configured between the individual shearing elements of the series of shearing elements of the rotor, are directed in opposite directions to through-openings for milk and air, which are configured between the individual shearing elements of the series of shearing elements of the stator.

6. The milk-frothing device according to claim 1, wherein a maximum radial extension of the rotor or of the stator is between 2 cm and 15 cm.

7. The milk-frothing device according to claim 1, wherein the rotor is capable of being rotated, relative to the stator, at a speed of rotation between 500 revolutions per minute and 7,000 revolutions per minute.

8. The milk-frothing device according to claim 1, wherein a drive of the rotor is via a motor-driven shaft.

9. The milk-frothing device according to claim 1, further comprising: a housing that encapsulates the rotor; at least one permanent magnet fixed in or on the rotor; and at least one coil fixed in or on the housing and capable of being supplied with electrical current for driving the rotor.

10. The milk-frothing device according to claim 1, further comprising: at least one supply channel configured for supplying the milk and the air into the dynamic mixing unit, the at least one supply channel being oriented, at least in portions, parallel to an axis of rotation of the rotor.

11. The milk-frothing device according to claim 10, further comprising: a control unit having one or more of the following characteristic parameters of the milk-frothing device is/are adjustable: speed of rotation of the rotor, quantity of milk supplied to the dynamic mixing unit per unit of time, quantity of air or quantity of air-steam mixture supplied to the dynamic mixing unit per unit of time, mixing ratio of air and steam of an air-steam mixture supplied to the dynamic mixing unit, or temperature of the steam in an air-steam mixture supplied to the dynamic mixing unit.

12. The milk-frothing device according to claim 11, further comprising: a temperature sensor configured to detect a temperature of the frothed-up milk discharged out of the dynamic mixing unit is detected, wherein the control unit is a control- and regulating unit, with which, using the temperature of the frothed-up milk detected with the temperature sensor, one or more of the following characteristic parameters of the milk-frothing device is/are regulatable: speed of rotation of the rotor, quantity of milk supplied to the dynamic mixing unit per unit of time, quantity of air or quantity of air-steam mixture supplied to the dynamic mixing unit per unit of time, mixing ratio of air and steam of an air-steam mixture supplied to the dynamic mixing unit, or temperature of the steam in an air-steam mixture supplied to the dynamic mixing unit.

13. The milk-frothing device according to claim 12, wherein the temperature sensor is disposed in or on the discharge channel.

14. The milk-frothing device according to claim 1, wherein the dynamic mixing unit is configured to be heated.

15. The milk-frothing device of claim 1, further comprising: a drinks preparer configured to prepare hot drinks.

16. The milk-frothing device according to claim 1, further comprising: a discharge channel configured to discharge the frothed and sheared milk and air out of the dynamic mixing unit, the discharge channel being oriented, at least in portions, parallel to an axis of rotation of the rotor.

17. The milk-frothing device according to claim 1, wherein the stator is configured to be heated.

Description

(1) Subsequently, the invention is described in more detail with reference to embodiments. There are thereby shown:

(2) FIG. 1 a first milk-frothing device according to the invention in a cross-section through the axis of rotation.

(3) FIG. 2 a three-dimensional plan view onto the rotor (FIG. 2a) and the stator (FIG. 2b) according to FIG. 1.

(4) FIG. 3 a plan view (in the direction of the axis of rotation) onto the rotor (FIG. 3a) and the stator (FIG. 3b) according to FIG. 1.

(5) FIG. 4a a section through the axis of rotation of a second milk-frothing device according to the invention.

(6) FIG. 4b a three-dimensional plan view onto the milk-frothing device from FIG. 4a.

(7) FIG. 5 a drinks preparer according to the invention in the form of a fully automatic coffee machine (merely the essential parts thereof according to the invention are illustrated).

(8) FIG. 1 shows, in cross-section in one plane, through which the axis of rotation 8 of the stator-rotor arrangement extends, a first milk-frothing device according to the invention. FIG. 2a shows a three-dimensional view and FIG. 3a shows a plan view (parallel to the axis of rotation 8) of the rotor 2 of this milk-frothing device. FIG. 2b shows a three-dimensional view and FIG. 3b shows a plan view (parallel to the axis of rotation 8) of the stator 1 of this milk-frothing device.

(9) As FIG. 1 shows, a supply channel 3 comprising two partial channels here leads parallel to the axis of rotation 8, but at a spacing therefrom, directly up to the rear-side surface 2R of a rotor 2. This supply channel 3 serves for supplying milk M and air L or milk M and an air-steam mixture to the rear-side surface 2R of the rotor 2. This rear-side 2R (apart from a gap) is surrounded in a form-fit by a housing portion 7 of the milk-frothing device. The housing portion 7 is connected rigidly to a stator 1 which is positioned on the front-side 2V of the rotor 2 and situated opposite the latter. The stator 1 surrounds the rotor 2 at the front-side 2V thereof, the housing portion 7 surrounds the rotor 2 at the outer circumference 5 thereof orientated away from the axis of rotation 8. Rotor 2 and stator 1 form the essential constructional elements of a dynamic mixing unit. The housing 7 and also the stator 1 connected to the latter surround the rear-side 2R, the outer circumference 5 and also the front-side 2V of the rotor 2 in a form-fit so that the inflowing fluid mixture L, M or L/D, M, as a result of the centrifugal forces of the rotor 2 rotating relative to the stator 1 and to the housing 7, is transported through a narrow gap between housing 7 and rotor rear-side 2R firstly towards the outer circumference 5, then, as a result of the pressure of the fluid L, M or L/D, M which flows subsequently via the supply pipe 3 out beyond the outer circumference 5 of the rotor (through a gap between the outer circumference 5 and the housing portion 7 surrounding the rotor 2), is pressed towards the front-side 2V of the rotor 2 and finally, because of the mentioned pressure between the front-side 2V of the rotor 2 and the surface of the stator 1 situated opposite the front-side 2V of the rotor 2 (i.e. between the shearing elements TOR of the rotor 2, on the one hand, and the shearing elements 10S of the stator 1, on the other hand, see subsequently) flows from the outer circumference 5 of the rotor 2 towards the axis of rotation 8, where said fluid mixture is discharged out of the dynamic mixing unit via a discharge channel 4 extending parallel to the axis of rotation 8. Frothing-up of the inflowing fluid mixture L, M or L/D, M is thereby effected during throughflow of the shearing elements 10R, 10S to form milk froth MS.

(10) The path of the fluid mixture via the supply channel 3, along the rear-side 2R of the rotor 2 from near the centre 6 of the rotor towards the outer circumference 5 of the rotor 2, beyond the outer circumference 5 to the front-side 2V of the rotor 2 through between the shearing elements 10R, 10S and back towards the centre 6 of the rotor and also finally via the discharge channel 4 is characterised in FIG. 1 by arrows (illustrated only for the quantity of fluid flowing past the above-situated outer circumferential side 5). The force to be applied on the front-side 2V of the rotor 2 against the rotation of the rotor 2, in order to press the fluid mixture through the shearing elements 10R, 10S for the frothing-up, is produced by the pressure generated by means of the pump 19 and the compressed air source 21 upstream of the supply pipe portion 3 (cf. FIG. 5). A pressure in the dynamic mixing unit of approx. 600 to 700 mbar is thereby sufficient.

(11) The outer diameter of the stator portion surrounding the rotor 2 on the outer circumferential side is here 7 cm. Housing 7 and stator 1 surround the rotor (apart from the supply pipe 3 and the discharge pipe 4) in a fluid-impermeable manner.

(12) The drive of the rotor 2 in the case of the first milk-frothing device according to the invention, according to FIGS. 1 to 3, is effected via a motor-driven drive shaft 12 rotating about the axis of rotation 8.

(13) FIGS. 2a and 3a show the construction of the rotor 2 of the first milk-frothing device according to the invention or the dynamic mixing unit thereof. The rotor 2 is configured as an essentially flat, rotationally-symmetrical disc which has a diameter of 6.5 cm. On the front-side 2V to be orientated towards the stator 1, this disc has a plurality (here: 3) of series of shear elements 9R (here: series 9R-1, 9R-2 and 9R-3). The direction of rotation of the rotor 2 during rotation about its centre 6 or about the axis of rotation 8 of the dynamic mixing unit is characterised with R (see arrow).

(14) Each series of shearing elements 9R consists of a large number of individual shearing elements 10R which protrude in the form of block-shaped pins from the surface 2V of the rotor 2 (and hence directed towards the stator 1), i.e. are configured as projections. Between directly adjacent shearing elements 10R of one series, respectively gap-shaped through-openings 11R are configured. The individual shearing elements 10R of each series 9R are positioned on a circle about the centre 6. The three series of shearing elements 9R therefore form respectively circular rings of projections which are positioned concentrically about the centre 6 or rotate about the axis of rotation 8 (in the rotating state R). The individual series of shearing elements or circular rings 9R are thereby positioned, viewed from the centre 6 towards the outer circumference 5 of the rotor 2, radially at a spacing from each other such that a series of shearing elements 9S of the stator 1 can engage respectively between two adjacent series of shearing elements 9R of the rotor 2 in a form-fit (apart from a residual, narrow gap with a gap extension of approx. 0.3 mm).

(15) In the case of the stator 1, the series of shearing elements 9S (concentrically about the axis of rotation) and also the shearing elements 10S (projections directed towards the rotor 2) and through-openings 11S of these series are configured analogously to the rotor 2.

(16) In the state assembled to form the finished dynamic mixing unit (cf. FIG. 1), there are hence configured, viewed along the axis of rotation 8, overlapping series of shearing elements 10R of the rotor 2, on the one hand, which are positioned alternately and engaged in each other, and of shearing elements 10S of the stator 1, on the other hand. If the rotor 2 rotates relative to the stator 1, the fluid L, M or L/D, M pressed through from the outer circumference 5 at the front-side 2V of the rotor 2 towards the centre 6 is hence sheared every time it passes through through-openings 11 of a series (for example: of the through-openings 11R of a series of shearing elements 9R of the rotor 2) and flows via the narrow gap towards the directly adjacent series of shearing elements (for example towards the adjacent series of shearing elements 10S of the stator 1). As the comparison of the stator shown in FIGS. 2b and 3b with the rotor shown in FIGS. 2a and 3a shows, a first shearing is hence effected, during the flow from the outer circumference 5 towards the centre 6, during crossing from the through-openings 11S of the outer series of shearing elements 9S-4 of the stator 1 via the gap between the latter and the outer series of shearing elements 9R-1 of the rotor into the through-openings 11R of the outer series of shearing elements 9R-4 of the rotor 2, subsequently a second shearing is effected upon crossing from the outer series of shearing elements 9R-4 of the rotor 2 via the gap between the latter and the second-outermost series of shearing elements 9S-3 of the stator 1, thereafter a third shearing is effected upon crossing from the second-outermost series of shearing elements 9S-3 of the stator 1 into the adjacent second-outermost series of shearing elements 9R-3 of the rotor 2 etc.

(17) As FIGS. 2 and 3 show, the number of shearing elements 10R, 10S per series of shearing elements increases in the case of the individual series of shearing elements 9R, 9S from the centre 6 towards the outer circumference 5 both in the case of the rotor 2 and in the case of the stator 1. The individual series or circular rings of shearing elements 9R, 9S have shearing elements 10R, 10S of a slightly different shape (cf. in particular the plan view of FIGS. 3a and 3b), this optimises, on the one hand, the dwell time in the dynamic mixer, on the other hand, it increases the shearing effect and hence ensures, on the one hand, homogenisation and stabilisation of the froth and, on the other hand, the stability of the froth.

(18) Viewed along the circular circumference of the series of shearing elements, the through-openings 11R, 11S of the individual series of shearing elements 9R, 9S have a gap width of approx. 2 mm. As can be detected in FIGS. 3a and 3b (these show the front-side 2V of the rotor 2 in plan view, cf. FIG. 3a, and the side of the stator orientated towards this front-side 2V after assembling the rotor-stator system, cf. FIG. 3b), the fluid through-openings 11R configured between the individual shearing elements 10R of one series of shearing elements 9R of the rotor 2 are directed in opposite directions to the fluid through-openings 11S configured between the individual shearing elements of the respectively adjacent series of shearing elements 9S of the stator 1 (this is detectable in the tilting of the longitudinal axis of the through-openings 11R, 11S, which is directed in the same direction in the case of the rotor 2 and in the case of the stator 1 in FIGS. 3a and 3b, relative to the radial direction from the centre 6 to the outer circumference 5).

(19) The drive of the rotor 2, only indicated here, via the motor-driven shaft 11 allows rotor speeds of rotation between 500 l/min and 7,000 l/min. By varying the rotor speed of rotation within this wide speed of rotation range, the froth quality and froth consistency can be adjusted continuously and very variably.

(20) FIGS. 4a (section in a plane in which the axis of rotation 8 extends) and 4b (three dimensional plan view onto the stator 1 which, together with the housing 13, surrounds the rotor 2, not visible here) show a second milk-frothing device according to the invention. The construction thereof thereby follows basically the construction described for the frothing devices of FIGS. 1 to 3b (the same applies to the mode of operation) so that merely the differences are described subsequently. Identical reference numbers hence denote identical components.

(21) As in FIG. 1 (housing 7), the housing 13 of the dynamic mixing unit surrounds not only the rear-side 2R of the rotor 2 but also the outer circumference 5 thereof. The stator 1 (which is connected rigidly and in a fluid-impermeable manner to the housing 13 surrounding the rotor 2) forms here an essentially disc-shaped plate which is situated opposite the front-side 2V of the rotor and carries the series of shearing elements 9S. The housing 13 and the stator 1 surround the rotor 2 in a fluid-impermeable manner (apart from the opening of the channels 3, 4).

(22) On the rear-side 2R of the rotor 2, offset radially outwards from the centre 6 of the rotor or from the axis of rotation 8, in total two individual supply channels 3a, 3b (which extend parallel to the axis of rotation 8) lead from outside, via the housing wall of the housing 13, to the rear-side 2R of the rotor 2. The first supply channel 3a serves for supply of air or an L/D mixture, the second supply channel 3b serves for the supply of milk M into the interior of the dynamic mixing unit. On the front-side 2V of the rotor, the single discharge channel 4 likewise leads from the centre 6, offset slightly radially outwards and also parallel to the axis of rotation through stator body, out of the fluid-impermeable composite of housing 13 and stator 1 to the outside (discharge of the produced milk froth (MS).

(23) The drive of the rotor 2 or the rotation R thereof is effected electromagnetically: for this purpose, a plurality of permanent magnets 14 is integrated on the rear-side 2R of the rotor 2 in this. Viewed along the axis of rotation 8 at the level of the permanent magnets 14, a coil 15 is wound over the housing 13 on the outer circumferential side, which coil can be supplied with electrical current. The construction and also the arrangement of the coil 15 and of the permanent magnets 14 is such that an electric motor rotary drive is produced.

(24) The variant shown in FIGS. 4a and 4b has the advantage that sealing problems of the motor-driven shaft (cf. FIG. 1), possibly occurring after long operational duration, can be avoided.

(25) As can be detected in FIG. 4b, a temperature sensor 16 is positioned on the discharge channel 4 of the dynamic mixing unit and is connected to a control- and regulating unit 17 of the milk-frothing device (cf. FIG. 5).

(26) The variant shown in FIGS. 4a and 4b also has the advantage that steam D can be conducted at a high temperature (up to 100 C.) via the first supply channel 3a, for disinfection via the flow path L or L/D into the interior of the rotor-stator system, an inflow of cleaning solution being able to be effected at the same time via the second supply channel 3b. Simultaneous rotation R of the rotor 2 hence enables optimum cleaning: chemical cleaning by means of high temperature with simultaneous mechanical cleaning by rotation.

(27) FIG. 5 shows an electrically operated coffee machine (fully automatic coffee machine) according to the invention with integrated milk-frothing device according to FIGS. 1 to 3 or according to FIGS. 4a and 4b. Only the essential features according to the invention of the fully automatic coffee machine are thereby shown.

(28) Milk M taken from an external container 18 is suctioned in via a supply pipe by a pump 19 of the fully automatic machine. Downstream of the pump 19, an air- or air-steam supply pipe opens into the fluid supply path on the output side of the pump leading towards the dynamic mixing unit 1, 2. The latter corresponds to the supply channel 3 in FIG. 1. If the dynamic mixing unit 1, 2 of FIGS. 4a, 4b is used (not shown here), then no upstream uniting of the air- or air-steam flow with the milk flow is effected, but rather the air L or L/D mixture is conducted via the first supply channel 3a and the milk M is conducted via the pump output side of the pat, which opens into the second supply channel 3b, into the dynamic mixing unit 1, 2.

(29) The air- or air-steam supply is effected as follows: for air supply, the fully automatic coffee machine comprises a compressed air source 21, via which the air L can be conducted into the pipe between pump 19 and dynamic mixing unit 1, 2. Upstream of the corresponding opening, a steam pipe opens into this air supply pipe, at the upstream end of which a hot steam source 20 is situated. Via the steam pipe, an optional steam component D can be added to the compressed air L (by means of which the result is not only frothing in the mixing unit 1, 2 by means of multiple shearing but also heating of the milk froth MS to be dispensed). Optionally (or alternatively to the steam source 20), also a heating unit (not shown here) can be provided, with which heating unit the dynamic mixing unit (preferably the stator 1 of the same) can be heated.

(30) The discharge channel 4 of the dynamic mixing unit 1, 2 for discharging the milk froth MS leads into a dispensing head 22 of the fully automatic coffee machine which is configured to dispense both the milk froth MS and the prepared coffee K (coffee-making unit not shown here) into an external cup T. A temperature sensor 16 is positioned on the discharge channel 4 (cf. FIG. 4b).

(31) A central control- and regulating unit 17 controls production and dispensing of the milk froth MS (and also the remaining functions of the fully automatic coffee machine), as follows: bi-directional control- and data lines 16a, 19a, 20a and 21a connect the central control- and regulating unit 17 to the temperature sensor 16, to the pump 19, to the steam source 20 and to the compressed air source 21. In addition, the unit 17 (not shown here) for controlling the speed of rotation of the rotor is connected to the dynamic mixing unit 1, 2.

(32) The unit 17 firstly controls the ratio of steam D and L of the L/D mixture which is added to the milk M. Thus, for example if it is detected via the temperature sensor 16 that the temperature of the milk froth MS is too low, the proportion of steam L) relative to the proportion of air L in the L/D mixture can be increased. The quantity of supplied L/D mixture relative to the quantity of milk M suctioned in via the pump 19 can be regulated via the speed of rotation of the pump 19: increasing the speed of rotation of the pump increases the conveyed quantity of the pump 19 and hence the proportion of milk M in the mixture of air L, steam D and milk M. Also complete switching off of the steam source 20 via the line 20a is possible so that cold milk froth MS can be produced and dispensed. 22 (after cooling the milk M in the external container 18).

(33) Alternatively to the basic construction shown in FIG. 5, the pump 19 can also be positioned, after the opening of the L/D pipe, into the supply pipe to the mixing unit 1, 2. Instead of heating the milk M via steam D, the steam source 20 can also be omitted: instead, a flow heater can be positioned between pump 19 and mixing unit 1, 2.