Abstract:
In a milk steamer, a changeover valve and a vent valve are connected to the inlet and the outlet of a steam-generating thermoblock to provide ready draining of water, and to mitigate condensation of steam that draws milk into the steam nozzle. In an automatic milk steamer, the height of the steam nozzle above the milk level is automatically set by interaction between a drive mechanism and a liquid level sensor.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to milk steamers and methods for operating such milk steamers. 
       BACKGROUND OF THE INVENTION 
       [0002]    The invention generally relates to a milk steamer in which water is heated in a so-called thermoblock in order to produce steam. The term “thermoblock” as used herein refers to a heat exchanger in which water is heated (e.g. by resistance elements) while it is pumped. In contrast, in a boiler the steam is dispensed only after the heating is finished. Generally boilers have a much higher thermal inertia with a resulting slower response to heat inputs. On the other hand, thermoblocks provide high heating rates and consequently consume considerable electric power while in operation. 
         [0003]    A milk steamer according to the present invention is provided with a steam outlet, as in the form of a nozzle, for steaming milk. The milk steamer may be a stand-alone device, or part of a larger machine, such as a coffee machine. 
         [0004]    EP1764014 describes milk steamer that employs a thermoblock for generating steam that is dispensed from a steam nozzle, such as may be used for steaming milk. The thermoblock may be evacuated by way of a two-way vent valve connecting an inlet side of the thermoblock to an evacuation outlet, while a two-way shut-off valve connects the outlet side of the thermoblock to the steam nozzle. This arrangement protects the pump from high temperature and back pressure and provides for the thermoblock to be readily emptied to reduce scale deposition. However under certain operating conditions, condensation of steam in the nozzle produces a vacuum that draws milk into the nozzle. Also, due to the quantity of steam that may be evacuated through the vent valve, this vented flow passes through a condenser, before being exhausted into the evacuation outlet. Moreover, complex control and timing of valve actuations is needed. 
         [0005]    Automatic steaming devices are known which allow anyone to obtain frothy milk without any skill, however many of these prior art devices have various drawbacks including unsatisfactory or inconsistent flavour and foam texture, lack of versatility, and high complexity and manufacturing costs. It will be understood that there is an unmet need for improved automatic steaming devices which address these drawbacks. 
         [0006]    It is an object of the present invention to overcome or substantially ameliorate the above disadvantages or more generally to provide an improved milk steamer. 
       DISCLOSURE OF THE INVENTION 
       [0007]    According to one aspect of the present invention there is provided a milk steamer comprising:
       a water reservoir;   a supply line connected to the water reservoir;   a pump connected in the supply line for generating a water flow;   a thermoblock for generating steam;   a changeover valve for selectively connecting an inlet of the thermoblock to the supply line;   a steam outlet, the steam outlet being supplied during use with steam from an outlet of the thermoblock; and   a vent valve for alternately connecting the steam nozzle to either the outlet of the thermoblock or an evacuation outlet.       
 
         [0015]    Preferably the milk steamer further comprises a return line connected between the water reservoir and the changeover valve, wherein the changeover valve alternately connects the inlet of the thermoblock to either the supply line or the return line. 
         [0016]    Preferably both the changeover valve and vent valve are three-way two-position valves that are solenoid actuated, and spring biased to respective normal positions, wherein in the normal position of the changeover valve the inlet of the thermoblock is connected to the return line, and in the normal position of the vent valve the steam outlet is connected to the evacuation outlet. 
         [0017]    Preferably the evacuation outlet is located at a lower position than the inlet side of the thermoblock. 
         [0018]    Preferably the changeover valve and vent valve of both moved to and from their normal position substantially simultaneously. By having the changeover valve and vent valve both moved to and from their normal position substantially simultaneously the control of the machine is simplified compared to prior art where delays must be implemented between valve operations. 
         [0019]    In another aspect the invention comprises an automatic milk steamer for use with a vessel positioned on a support, comprising:
       a steam generator;   a steam nozzle in communication with the steam generator;   a drive mechanism for raising and lowering one of the steam nozzle and the support with respect to the other of the other of the steam nozzle and the support;   a sensing probe connected to the nozzle including a level sensor for sensing a liquid level and providing a liquid level signal, and a temperature sensor for sensing a liquid temperature and providing a liquid temperature signal, and   a controller for controlling the drive mechanism in response to the liquid level signal so as to position the nozzle at a height relative to a liquid level in the vessel.       
 
         [0025]    Preferably the sensing probe includes to the controller. 
         [0026]    Preferably the drive mechanism raises and lowers the one of the steam nozzle and the support on a linear path. 
         [0027]    Preferably the support is mounted to a housing of the automatic milk steamer, 
         [0028]    Preferably the level sensor is a resistive level sensor, and a tip of the sensing probe protrudes below a tip of the steam nozzle. Alternatively, the level sensor may be a float type sensor, a magnetic, capacitance, optical, or other type of level sensor. 
         [0029]    Preferably the drive mechanism includes motor-driven screw for raising and lowering one of the steam nozzle and the support. Alternatively, the drive mechanism may comprise a linear actuator, a rope and pulley system, or any of the many well known raising and lowering mechanisms. 
         [0030]    In yet another aspect the invention comprises a milk steamer, comprising:
       a steam generator;   a steam nozzle in communication with the steam generator;   a sensing probe connected to the steam nozzle including a level sensor for sensing a liquid level and providing a liquid level signal, and a temperature sensor for sensing a liquid temperature and providing a liquid temperature signal;   a controller for receiving the liquid level signal, and   an indicator operatively coupled to the controller and responsive to the liquid level signal for providing an indication to the user of that the nozzle is disposed at a predetermined position relative to a liquid level in the vessel.       
 
         [0036]    The indicator may comprise an audible, visual, or other indicator. For instance, the indicator may comprises a sound generator, or light generator, which is switched on or off by the controller when the nozzle is disposed at the predetermined position relative to the liquid level. Alternatively the indicator may comprises a vibrator for vibrating the steam nozzle, which is vibrator switched on or off by the controller when the nozzle is disposed at the predetermined position relative to the liquid level. In another aspect the invention provides a method of operating the above-described automatic milk steamer comprising:
       a) actuating the drive mechanism to raise or lower the one of the steam nozzle and the support;   b) monitoring the liquid level signal and, when a first liquid level is detected, stopping the drive mechanism and activating the steam generator to dispense steam from the steam nozzle.       
 
         [0039]    Preferably the method further comprises the step of:
       d) monitoring the temperature signal and, when a first temperature level is detected, stopping the steam generator.       
 
         [0041]    Preferably the method further comprises the step of:
       e) actuating the drive mechanism to raise or lower the one of the steam nozzle and the support.       
 
         [0043]    This invention provides an automatic milk steamer which is effective and efficient in operational use, and which produces consistent flavour and foam texture. The device may be economically constructed and has an simple overall design that minimizes manufacturing costs and maximizes performance. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0044]    Preferred forms of the present invention will now be described by way of example with reference to the accompanying drawings, wherein: 
           [0045]      FIG. 1  is a schematic of a milk steamer according to the invention, and 
           [0046]      FIGS. 2 and 3  are schematic illustrations of first and second embodiments respectively of an automatic milk steamer. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0047]    Referring to  FIG. 1 , a milk steamer generally comprises steam generator  31  connected to a steam nozzle  19  which, in use, is inserted into a vessel containing the milk to be steamed and foamed. The steam generator  31  includes a water reservoir  10  with a supply line  11  connected to the water reservoir  10  and a pump  12  connected in the supply line  11  for generating a water flow. A filter  13  may be connected in the supply line between the water reservoir  10  and the pump  12 . A return line  15  may carry a return flow to the water reservoir  10 . A steam-generating thermoblock  17  is supplied with water via a changeover valve  14  that selectively connects an inlet  16  of the thermoblock to the supply line  11 . The changeover valve  14  may alternately connect the inlet  16  of the thermoblock to either the supply line  11  or the return line  15 . An outlet  18  of the thermoblock is connected via a vent valve  20  to the steam nozzle  19 . Also connected to the vent valve  20  is an evacuation outlet  21 , which may be in the form of an open tray. The vent valve  20  alternately connects the steam nozzle  19  to either the outlet  18  of the thermoblock or the evacuation outlet  21 . 
         [0048]      FIG. 1  illustrates the vent valve  20  and changeover valve  14  in their first positions or normal states, as when no power is supplied to operate the machine. The vent valve  20  and changeover valve  14  may be three-way two-position valves, such as a solenoid-operated valves spring biased to the positions shown in  FIG. 1 . In this state, the vent valve  20  is positioned such that the steam nozzle  19  is connected to the evacuation outlet  21  and, by evacuating the steam nozzle  19  in this way, the possibility of condensing steam drawing milk into the nozzle  19  is mitigated or avoided. Likewise, with the changeover valve  14  in its normal state as illustrated, the inlet  16  of the thermoblock is connected to the return line  15  so any water in the thermoblock  17  may drain out through the return line  15  to the reservoir  10 . 
         [0049]    In use, a controller (not shown) may control, in addition to other components, the actuation of the vent valve  20  and changeover valve  14 , as well as the actuation of the pump  12 , and the heating elements (not shown) of the thermoblock  17 . Firstly, the thermoblock  17  is heated to its operating temperature, with the vent valve  20  and changeover valve  14  in their normal or first positions shown in  FIG. 1 . Some steam may be generated in the thermoblock  17  due to residual amounts of water, and this is vented by the changeover valve  14 . To generate and dispense steam from the steam nozzle  19 , both the vent valve  20  and changeover valve  14  may be simultaneously moved to their second positions (not shown), and the pump  12  is actuated to force water from the supply line  11  into the inlet  16  of the thermoblock  17  at a rate sufficient that steam is expelled through the vent valve  20  and out from the steam nozzle  19 . The pump  12  may be a metering pump, such as a positive displacement pump, driven in a controlled manner, as by a stepper motor, for instance, in order to produce a defined amount of steam. Alternatively, flow metering can be used to control the pump. 
         [0050]    To stop the generation and dispensing of steam, the changeover valve  14  and vent valve  20  may be simultaneously actuated and moved to their normal or first positions, as shown in  FIG. 1 , at the time the pump  12  is stopped. The water flow to the inlet  16  of the thermoblock is stopped, while the changeover valve  14  connects the inlet  16  of the thermoblock to the return line  15 . The flow of steam from the outlet  18  of the thermoblock into the vent valve  20  is stopped, and vent valve  20  connects the steam nozzle  19  to the evacuation outlet  21 . In this state steam pressure in the hot thermoblock  17  serves to evacuate the water from the inlet  16 , directing it through the return line  15  to the reservoir  10 . Steam in the steam nozzle  19  is vented through the vent valve  20  to the evacuation outlet  21 . Once evacuated in this way, a sudden cooling of the nozzle  19  will not produce a vacuum that draws milk into the nozzle. As the amount of the steam in the steam nozzle  19  and connecting line  22  is small, there is no need for a condenser in this connecting line  22  between the vent valve  20  and evacuation outlet  21 . 
         [0051]    Two embodiments of an automatic milk steamer are shown  FIGS. 2 and 3 , in which either the nozzle assembly  34  is raised and lowered ( FIG. 2 ) or the support  138  for supporting the vessel  35  is raised and lowered ( FIG. 3 ) in order to position the steam nozzle  19  at a suitable height relative to the milk level  36 . When so positioned, the jet of steam introduced into the milk both heats the milk, slightly caramelising it, and at the same time mixes in air which generates the foam. By accurately controlling the nozzle height relative to the milk level  36 , and monitoring the milk temperature, steamed milk with good flavour and foam texture can reliably be produced. 
         [0052]    The general construction of the nozzle assembly  34  is common in both embodiments, and may have a generally L-shaped form, protruding outwardly and downwardly from a housing section  39 ,  139  of the milk steamer. The nozzle assembly  34  includes the steam nozzle  19  and sensing probe  37 , and may serve to connect these elements. The nozzle assembly  34  may include a body  43  that encloses the connecting line  22  joining the nozzle  19  to the steam generator  31 , and the conductor  42  joining the sensing probe  37  to the controller  40 . 
         [0053]    In the embodiment of  FIG. 2  the nozzle assembly  34  may be mounted to move in vertical guides (not shown), while the support  38  may be fixed to the housing section  39 . In the embodiment of  FIG. 3  the support  138  may be mounted to move in vertical guides (not shown), while the nozzle assembly  34  may be fixed to the housing section  39 . 
         [0054]    A drive mechanism  50  for raising and lowering the steam nozzle  19  or the support  138  may include an upright screw (not shown) rotated by a motor (not shown) via a transmission, and a nut (not shown) engaged with the screw and connected to either the nozzle assembly  34  ( FIG. 2 ) or to the support  138  ( FIG. 3 ). 
         [0055]    The sensing probe  37  connected to the nozzle  19  includes a level sensor for sensing a liquid level and providing a liquid level signal, and a temperature sensor for sensing a liquid temperature and providing a liquid temperature signal. The sensing probe  37  is connected to the controller  40  in a circuit  41 . The level sensor may be a resistive level sensor and the temperature sensor a thermocouple. A tip of the sensing probe may protrude below a tip of the steam nozzle  19  such that, in use, the tip of the steam nozzle  19  is disposed above the milk level  36 . 
         [0056]    The controller  40  controls the drive mechanism  50  and a steam generator  31 , which may be of the type described above with reference to  FIG. 1 . In use, a vessel  35  holding milk is placed upon the support  38 ,  138  below the nozzle assembly  34 . A single start button (not shown) may be actuated by the user, whereupon the controller  40  actuates the drive mechanism  50  to raise or lower the steam nozzle  34  ( FIG. 2 ) or the support  138  ( FIG. 3 ) while monitoring the liquid level signal from the sensing probe  37 . When a first liquid level is detected, the controller  40  stops the drive mechanism  50  and activates the steam generator  31  to dispense steam from the steam nozzle  19 . While the steam is ejected, the controller  40  monitors the temperature signal from the sensing probe  37  and, when a first temperature level is detected, stops the steam generator  31 . The controller  40  may subsequently actuate the drive mechanism  50  to raise or lower the steam nozzle  34  or the support  138  which, optionally together with another indicator such as a sound or display, indicates the completion of the operation. 
         [0057]    In a further alternative embodiment (not shown) the nozzle assembly  34  may be fixed to the housing section  139  as in the embodiment of  FIG. 3  and the moving support  138  is an optional feature. In this alternative embodiment an indicator is operatively coupled to the controller and is responsive to the liquid level signal for providing an indication to the user of that the nozzle is disposed at a predetermined position relative to a liquid level in the vessel. In this way the user can employ the conventional manual technique, whereby the jug of milk is manually held beneath the steam nozzle  19 , but the indicator assists unskilled users, by alerting the user when the nozzle is disposed at the proper height relative to the milk level. The indication may take the form of an audible, visual, or vibratory alert that starts or stops when the steam nozzle  19  is properly positioned relative to the liquid level. 
         [0058]    Aspects of the present invention have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the scope thereof.