GRINDER, COFFEE MACHINE AND METHOD FOR GRINDING COFFEE BEANS

Abstract

The invention relates to a grinder for grinding coffee beans. The grinder has a first grinding tool and a second grinding tool which form a grinding gap and are rotatable relative to each other to grind coffee beans in the gap. A force generation device is arranged for applying a force, which is adjustable during operation, to one or both of the first grinding tool and second grinding tool, which force is transferable to the coffee beans. The invention also relates to a method for grinding coffee beans with the grinder for preparing a hot beverage.

Claims

1. A grinder for grinding coffee beans, comprising: a first grinding tool and a second grinding tool arranged relative to one another to form a grinding gap and to be rotatable relative to one another during operation of the grinder for grinding the coffee beans in the grinding gap; at least one force generation device arranged for applying a force which is adjustable during operation of the grinder to at least one of the first grinding tool and the second grinding tool, which force is transmittable to the coffee beans, wherein the force is directed that it presses the respective grinding tool to which the force is applied in a direction of the respective other grinding tool.

2. The grinder according to claim 1, further comprising a drive unit arranged to rotatably drive one of the two grinding tools while the second of the two grinding tools is arranged to stand still.

3. The grinder according to claim 1, wherein the force generation device acts upon at least one of the first and the second grinding tool.

4. The grinder according to claim 1, wherein the force generation device is arranged to act in each case upon the first grinding tool and upon the second grinding tool.

5. The grinder according to claim 1, wherein the grinder comprises one of a disc, roller and cone grinder.

6. The grinder according to claim 1, wherein the force generation device includes a pressure spring, wherein the grinding gap extends across a plane and the spring exerts an axial force perpendicularly to the plane on at least one of the first and second grinding tool.

7. The grinder according to claim 1, wherein the force generation device comprises at least one spring and a device for setting a pre-tensioning force of the spring.

8. The grinder according to claim 1, wherein the force generation device is operable based on a pneumatic operating principle.

9. The grinder according to claim 1, wherein the force generation device is operable based on a fluid operating principle.

10. The grinder according to claim 1, wherein the force generation device is operable based on an electromagnetic operating principle.

11. The grinder according to claim 1, further comprising a control unit, wherein the grinder is operable for setting a pre-tensioning force of the spring by the control and as a function of at least one of: a) the type of coffee beans and their degree of roasting; b) the temperature of the grinder; and c) a degree of wear of the grinder.

12. The grinder according to claim 1, further including a temperature sensor for determining a thermal expansion of the grinder, wherein the force generation device is controlled as a function of the thermal expansion.

13. The grinder according to claim 1, further including an adjustable stop arranged for setting a minimum grinding degree.

14. A coffee machine, including at least one grinder according to claim 1.

15. A method for grinding coffee beans for the preparation of a hot coffee beverage by a grinder according to claim 1, comprising the following steps: a) placing coffee beans in the grinding gap between the first and second grinding tools; b) applying an adjustable process force during operation, to at least one of the first and second grinding tools in a direction of the respective other grinding tool by the force generation device; and c) outputting ground coffee with a defined grinding degree.

16. The method according to claim 15, further including setting a magnitude of the adjustable process force as a function of at least one of a type of coffee beans, a power of a motor of the grinder, a temperature of the grinder and a number of previous grinding passes.

17. The method according to claim 16, including, the setting of the magnitude includes taking into account a desired grinding degree of the ground product.

18. The method according to one of claims 15, including resolving a blockage of the grinding tools caused by impurities, such as pieces of wood, stones, in the beans by discontinuing the applying of force.

19. The method according to claim 17, wherein the setting of the magnitude includes setting a product-specific grinding degree on a fully automatic coffee machine by applying the adjustable force.

20. A method for preparing coffee with a fully automatic coffee machine utilizing the grinding method of claim 1, including grinding the coffee beans with the grinder and preparing coffee of a specific type in a brewing unit from the ground coffee beans and water, including automatically setting or changing over a grinding degree depending on a type of the coffee before grinding when the type of coffee is changed.

21. The method according to claim 20, wherein the setting of the magnitude of the adjustable process force includes controlling by a control loop that includes a control and/or evaluation unit and at least one force measuring device having at least one force sensor.

22. The grinder according to claim 1, further including at least one force measuring device having at least one force sensor, wherein the at least one force sensor is connected directly or indirectly to at least one of the first and second grinding tools.

23. The grinder according to claim 22, further including a control loop that includes a control and/or evaluation unit and at least one force measuring device having at least one force sensor, wherein the at least one force sensor is connected to the control and/or evaluation unit and to form a measuring device of the control loop.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0069] In the following, the invention is described in more detail with reference to the drawings by means of an exemplary embodiment. The figures only serve to explain the invention in more detail and are not restrictive for the invention. Individual features described can also be transferred to further embodiment variants within the scope of general technical knowledge, wherein:

[0070] FIG. 1: is a schematic front view in section of an embodiment of a grinder according to the invention for grinding coffee beans;

[0071] FIG. 2: is a diagram showing the results of a series of grinding tests;

[0072] FIG. 3: is another diagram showing the results of a series of grinding tests;

[0073] FIG. 4: is a schematic front view in section of an embodiment of a grinder according to the invention for grinding coffee beans; and

[0074] FIG. 5: is the front view of the grinder according to FIG. 1 with a force sensor device.

DETAILED DESCRIPTION

[0075] FIG. 1 is a schematic front view in section of the device according to the invention, in the form of a grinder 1 for grinding coffee beans 5. Grinder 1 has a first grinding tool 2. The first grinding tool 2 is non-rotatably mounted in a housing not shown here. In this respect, the first grinding tool 2 is at a standstill during operation of grinder 1.

[0076] The first grinding tool 2 is designed here as a grinding disc and therefore has a cylindrical envelope geometry and a central opening 3. The grinding tool 2 can also be designed differently, e.g. as a grinding cone. The opening 3 can be penetrated by a feed hopper 4. Coffee beans 5 to be ground are fed to the device 1 through the feed hopper 4 and the opening 3. The grinder 1 can also be provided for grinding other semi-luxury foods or foodstuffs but is preferably intended for grinding coffee beans 5. The feed hopper 4 is advantageously designed to prevent undesirable bridge formation of the coffee beans 5 in the feed hopper 4.

[0077] The first grinding tool 2 has a conical recess 6 on its side facing away from the feed hopper 4. The recess 6 has at least one grinding edge 7.

[0078] The grinder 1 has a second grinding tool 8. The second grinding tool 8 is arranged coaxially to the first grinding tool 2 and below the first grinding tool 2. The term “below” refers to the drawing plane of FIG. 1. The second grinding tool 8 is rotatably mounted in a housing not shown here. In this respect, the second grinding tool 8 rotates during operation of grinding tool 1.

[0079] The second grinding tool 8 also has a cylindrical envelope geometry. The second grinding tool 8 can also be designed differently, e.g. as a grinding cone. The second grinding tool is rotatable relative to the first grinding tool. In this case, the second grinding tool 8 is non-rotatably connected to a drive shaft 9 of a motor 10 so that the second grinding tool 8 is set in rotation while the first grinding tool 2 stands still. This is advantageous, but not mandatory.

[0080] Alternatively, the first grinding tool can be rotatable or rotated during operation while the second grinding tool 8 stands still. It is also possible that both grinding tools can be rotated, e.g. in opposite directions of rotation and/or at different speeds, so that there is always a relative movement between the two grinding tools 2, 8. Alternatively, a shaftless direct drive is also possible, in which one of the grinding tools 2, 8 is the rotor of the motor 10, or an indirect drive, in which the motor 10 acts upon one of the grinding tools 2, 8 via a transmission. The second grinding tool 8 has a conical recess 11 on its side facing away from the motor 10. The recess 11 has at least one grinding edge 12.

[0081] The conical recess 6 of the first grinding tool 2 and the conical recess 11 of the second grinding tool 8 thus form a kind of double conical grinding chamber 13, which opens at its outer circumference into a grinding gap 14. A collecting device (not shown here) can be connected to the grinding gap 14, which collects the coffee beans, preferably coffee powder, emerging from the grinding gap 14 and feeds the powder into an extraction process.

[0082] The grinder 1 has at least one force generation device 15. In this case, the force generation device 15 acts upon the first grinding tool 2, which means that a respective force F acts continuously, i.e. during operation while one or both grinding tools are rotating, upon coffee beans located between the first grinding tool 2 and the second grinding tool 8. This is advantageous, but not mandatory. The force generation device 15 can also act upon the second rotatable grinding tool 8 or upon both grinding tools 2, 8.

[0083] Here, the force generation device 15 comprises two pressure springs 16, which can be pretensioned by a corresponding device 17, for example by a servomotor, by a variable pretension path X, so that the respective force F, which acts upon the first grinding disc 2 and thus, during operation upon the coffee beans, can be changed or adjusted in its amount.

[0084] The force generation device 15 can also be designed differently than shown in FIG. 1. In this case, the force effect is essential, wherein the amount of force F is preferably variable or adjustable. In this case, the force generation device 15 can also be designed in such a way that the amount of force F is controlled automatically and/or infinitely variable depending on the higher-level operating parameters of a coffee machine.

[0085] This makes it advantageously possible to carry out a defined presetting of a grinding degree C, since the force F correlates with the grinding degree C, i.e. the size distribution of the ground product particles, characterized by the particle size of the 50% median of the ground coffee, which will be explained below.

[0086] In addition, the force acting upon the coffee beans by the grinder 1 can be set advantageously by the force generation device, depending on the coffee beans 5 to be ground and the desired grinding degree C. Preferably, data records regarding the grinding degree C and the bean type and the force to be generated by the force generation device are stored on a data memory of a control and/or evaluation unit 18 for controlling a coffee machine and in particular the grinder 1. The aforementioned control and/or evaluation unit 18 can be assigned to the grinder 1 or be part of a coffee machine, e.g. a fully automatic coffee machine.

[0087] A setting of the grinding degree C can thus be adjusted to match the specific bean (e.g. hard/heavily roasted beans vs. less heavily roasted café crème beans). See also FIG. 3 in this respect.

[0088] Alternatively, the type of beans can also be determined by the difference in power of the grinding efficiency by means of which the motor 10 is operated.

[0089] Furthermore, the force-controlled adjustment of the grinding degree C allows a permanent reproducibility of the grinding degree C even in case of grinding tool wear. For this purpose, a characteristic curve for wear over time can be stored for each bean type. The number of grinding processes can be weighted differently depending on the bean type used. Thus, for example, after 100 grinding processes of a “hard” bean type, a readjustment can be made by means of the device 17.

[0090] Likewise, the force-controlled setting of the grinding degree C can be used advantageously to compensate for thermal expansion effects, in particular of the grinding tools 2 and 8. For this purpose, a temperature sensor 23 (see FIG. 5) can detect the heat of the coffee beans as they leave the grinder 1, represented by the double arrow—dashed line between the arrow at the output of the grinder and the temperature sensor 23, which has an output leading to the control and/or evaluation unit 18 which, taking into account the coefficients of thermal expansion of the material of the grinding tools, accordingly adjusts the force of the force generation device 15, in particular the pretensioning force of the pressure springs 16.

[0091] Furthermore, manufacturing inaccuracies of the grinding tools 2, 8, such as axial run-out tolerances of the grinding tools 2, 8 have a significantly lower disturbing influence on the “grinding degree zero setting” of grinder 1 than in other grinding devices.

[0092] Consequently, there are advantageously lower fluctuations of a grinding efficiency O of the grinder 1 and the generated grinding degree C during operation of the grinder 1.

[0093] The grinder 1 described here opens up the possibility of changing the grinding degree C of coffee beans, including espresso beans, in a force-controlled manner via the force generation device 15. The inventive idea is based on a relationship between the force F acting upon the grinding tools 2, 8 and the resulting distribution of the particle size of the coffee beans. The narrower the grinding gap 14 is, the finer is the ground product produced and the greater the reaction force with negative sign −F with which the grinding tools 2, 8 are pressed apart. In embodiments according to the prior art, this force is absorbed by the grinding housing via the upper grinding tool.

[0094] The relationship between a fixed geometry of the grinding tools 2, 8 and the resulting relationship between the amount of force and the grinding degree C can be determined empirically (see FIG. 2). The knowledge gained from this can be used to permanently and precisely adjust the grinding degree C of the device 1. If the magnitudes of the forces are known, they can be specified in certain gradations in order to produce a specific grinding degree C (see also FIG. 3).

[0095] FIG. 3 shows the results of a grinding test series. In this case, the upper grinding disc 2 was subjected to different forces F and then three grinds were performed with the Bacio Nero bean. The coffee powder was then measured with a particle measuring device (measurement based on laser diffraction). The different grinding samples correspond to the three characteristic curves fineness measurement 1-3, wherein the median of the fineness distribution (grinding degree C) is used as characteristic in each case.

[0096] At the same time the grinding efficiency O of the device 1 was noted, i.e. the output grinding quantity of the device 1 per second. The device 1 was controlled by the motor 10 with power supply 230V, 50 Hz for 5 s each. FIG. 3 considers the influence of the amount of force F on the grinding degree C and the grinding efficiency O when grinding different beans. The bean types Bacio Nero, La Tazza Verde (Melitta) and a reference type were ground. In this case again, grinding efficiency O and grinding degree C were recorded at different amounts of force F acting upon the grinding tools 2, 8.

[0097] Experiments have therefore shown that there is a good correlation between grinding efficiency O and grinding degree C of a bean, provided that the production accuracy of the grinding tools 2, 8 is within a certain tolerance (see FIG. 2 and FIG. 3). From the grinding efficiency O of different grinders, it is therefore possible to draw conclusions about the produced grinding degree C with a high degree of accuracy, provided that the behavior of the grinding tools 2, 8 is known.

[0098] Under these conditions, a bean-specific force F can be inferred, with which a desired particle size distribution or a desired grinding degree C can be achieved. With the help of a database, in which the behavior of a reference roast and reference bean is stored, a control of the force F can then be performed in order to set the desired particle size distribution or the desired grinding degree C for the current roast and bean. As soon as the grinding efficiency O changes to a corresponding force F, because another bean or roast is used or the batch of a roast or bean type can be ground differently, the system regulates independently by a factor that depends on the grinding degree. This means that the force F is adjusted in order to obtain a desired particle size distribution or a desired grinding degree C.

[0099] Furthermore, for presetting a fully automatic coffee machine, a grinder-specific determination of the relationship between grinding efficiency O and grinding degree C is conceivable. In this way, increased accuracy can be generated for a specific grinder and the roast or bean type to be ground in it, in order to set a required grinding degree C at a specified amount of force F.

[0100] The grinding efficiency O of device 1 can be determined by means of already known methods:

[0101] An indirect possibility is to use a cake height of the coffee powder in the extraction process at a given contact pressure to infer the weight of the coffee powder provided for the extraction process. A piston coffee machine offers this possibility due to the already existing brewing unit. Since the control time of the grinder is specified, the grinding efficiency O can then be inferred.

[0102] A direct possibility is to weigh out the coffee powder. This can be automated by grinding in a set drawer and controlling it with a load cell.

[0103] Another possible application of a force-controlled setting of the grinding degree C is the combination of the device 1 with a regulation of the contact time between brewing water and coffee powder. To produce a constant beverage quality with a constant proportion of dissolved flavorings, a constant quantity of coffee powder with identical grinding degree C must be passed through by a specified amount of water within a certain time. Other basic conditions such as water temperature, contact pressure and brewing pressure must also remain as constant as possible during the brewing process so that the swelling behavior of the coffee is comparable and the contact time between the brewing water and the coffee powder remains identical.

[0104] A further embodiment of the grinder 1 is shown in FIG. 4 which, in comparison to FIG. 1, shows a rolling element 19 arranged between the grinding tool 2 and the pressure springs 16. It can also be a rolling bearing, e.g. a ball bearing or a needle bearing with a rolling element cage, wherein the pressure spring rests on the rolling element cage. This can extend coaxially to the feed hopper 4. The rolling element bearing allows rotation of the grinding tool 2 without the connection point of the respective pressure spring rotating with it.

[0105] This means that force can also be applied to a rotating tool element and, for example, force can also be applied to both tool elements.

[0106] FIG. 5 shows the front view of the grinder according to the invention and FIG. 1 with the addition of one or more force sensor devices 20 arranged in cooperation with one of the grinding tools 2, 8. In this case, two sensor devices 20 are shown. A first force sensor 21 is in interaction with the grinding tool 8 at a standstill, whereas a second force sensor 22 is in interaction with the first grinding tool 2. Each force sensor 21, 22 can be directly or indirectly connected to the corresponding grinding tool 2, 8.

[0107] The force sensors 21, 22 can, for example, be a pressure sensor (e.g. a load cell or a hydraulic pressure sensor), which respectively records the force during a grinding process by direct or indirect measurement.

[0108] Each force measuring device 20 is connected to the control and/or evaluation unit 18, as shown by the arrows in FIG. 5, and forms a measuring device of a control loop. The control and/or evaluation unit 18 has at least one target value/actual value comparator and a manipulated variable generator, which is coupled to an electrical fineness adjustment of the grinder 1, which is not shown, but can easily be imagined.

[0109] Since the axial force/fineness ratio of different beans in a grinder can be determined empirically, the grinder 1 is able to electrically set/adjust desired grinding degrees and to regulate them against disturbing factors (temperature, bean change, grinding disc exchange) with this control loop.

[0110] This results in the following advantages: [0111] 1. compensation of thermal expansion effects; [0112] 2. quick initial adjustment of a grinder (in particular when changing the grinding tool); [0113] 3. fineness adjustment during bean change; and [0114] 4. direct regulation of the grinder 1 with regard to particle fineness (see indirect regulation via extraction time of the coffee cake).