阅读说明：本技术 设置成提供一定剂量的分层研磨咖啡的咖啡研磨机以及相关方法 (Coffee grinder arranged to provide a dose of layered ground coffee and related method ) 是由 A·迪奥尼西奥 R·加提 A·帕伦蒂 G·安吉罗尼 L·格雷尼 于 2020-01-14 设计创作，主要内容包括：本申请公开了一种用于研磨咖啡豆和直接在过滤器篮中形成一定剂量研磨咖啡的咖啡研磨机,其中,该研磨咖啡有底层研磨咖啡和相邻层研磨咖啡,该底层研磨咖啡有第一平均颗粒尺寸,该相邻层研磨咖啡有第二平均颗粒尺寸,该咖啡研磨机包括：研磨部件,用于研磨咖啡豆；电马达,用于使至少一个研磨部件相对于另一研磨部件旋转；以及设置成在研磨咖啡豆用于形成剂量的过程中使得所述电马达的旋转速度在第一速度和第二速度之间变化的装置,其中,所述第二平均颗粒尺寸小于所述第一平均颗粒尺寸,且所述第一速度大于所述第二速度,或者所述第二平均颗粒尺寸大于所述第一平均颗粒尺寸,且所述第一速度低于所述第二速度。(A coffee grinder for grinding coffee beans and forming a dose of ground coffee directly in a filter basket, wherein the ground coffee has a bottom layer of ground coffee having a first average particle size and an adjacent layer of ground coffee having a second average particle size, the coffee grinder comprising: a grinding member for grinding coffee beans; an electric motor for rotating at least one grinding member relative to another grinding member; and means arranged to vary the rotational speed of the electric motor between a first speed and a second speed during grinding of the coffee beans for forming a dose, wherein the second average particle size is smaller than the first average particle size and the first speed is larger than the second speed, or the second average particle size is larger than the first average particle size and the first speed is lower than the second speed.)

1. Coffee grinder (1) for grinding coffee beans and forming a dose (D) of ground coffee in a filter basket (FT), wherein the ground coffee has a bottom layer of ground coffee having a first average particle size and an adjacent layer of ground coffee having a second average particle size, the coffee grinder comprising:

-a grinding member (3) for grinding coffee beans;

-an electric motor (2) for rotating at least one grinding member (3) relative to another grinding member (3); and

-speed variation means (4) arranged to vary the rotational speed of the electric motor (2) between a first speed and a second speed during grinding of coffee beans for forming a dose (D),

wherein

The second average particle size is less than the first average particle size and the first velocity is greater than the second velocity, or

The second average particle size is greater than the first average particle size, and the first velocity is lower than the second velocity.

2. The coffee grinder (1) according to claim 1, further comprising: a rotation counter for counting the number of rotations of the grinding member (3) relative to the other grinding member (3), wherein,

the speed variation means (4) is arranged to vary the speed from a first speed to a second speed in dependence on a set number of relative rotations of the grinding member (3) and the further grinding member (3).

3. The coffee grinder (1) according to claim 1, further comprising: a timer, wherein the timer is, for example,

the speed variation means (4) is arranged to vary the speed from a first speed to a second speed in dependence on a set period of time counted from the start of the activation of the electric motor (2).

4. The coffee grinder (1) according to claim 1, further comprising: a weighing means for calculating the mass of the dose of ground coffee, wherein,

the speed variation means (4) are arranged to vary the speed from a first speed to a second speed depending on the mass of the first part of the dose of coffee ground at the first speed.

5. Coffee grinder (1) according to any one of claims 1-4, wherein: the speed variation device (4) is arranged to vary the speed of the electric motor (2) stepwise.

6. Coffee grinder (1) according to any one of claims 1-4, wherein: the speed variation device (4) is arranged to continuously vary the speed of the electric motor (2).

7. Coffee grinder (1) according to any of the preceding claims, further comprising: an interface for selecting a speed profile for grinding a dose (D) of coffee.

8. Coffee grinder (1) according to any of the preceding claims, further comprising: an encoder (6) for detecting the rotational speed of the electric motor (2).

9. A method of grinding coffee beans in order to obtain a dose (D) of ground coffee in a filter basket (FT), the ground coffee having a bottom layer of ground coffee having a first average particle size and an adjacent layer of ground coffee having a second average particle size, the method comprising:

(a) providing a grinding member (3) for grinding coffee beans;

(b) -providing an electric motor (2) for rotating one grinding member (3) relative to the other grinding member (3); and

(c) during grinding, rotating the at least one grinding member (3) relative to the other grinding member (3) at a first speed and then at a second speed,

wherein the content of the first and second substances,

the second average particle size is less than the first average particle size and the first velocity is greater than the second velocity; or

The second average particle size is greater than the first average particle size, and the first velocity is lower than the second velocity.

10. The method of claim 9, further comprising: counting the number of rotations of the grinding member (3) relative to the other grinding member (3); and changing the speed from a first speed to a second speed according to a set number of relative rotations of the grinding member (3) and the further grinding member (3).

11. The method of claim 9 or 10, further comprising: the speed is changed from a first speed to a second speed according to a set period of time counted from the start of the activation of the electric motor (2).

12. The method of claim 9, 10 or 11, further comprising: the speed is varied from a first speed to a second speed in dependence on the mass of a first part of the dose of coffee ground at said first speed.

13. The method of any of claims 9-12, wherein: said speed change from the first start-up speed to the second speed can be performed continuously or stepwise.

Technical Field

The present invention relates to a machine for grinding coffee beans. The machine for grinding coffee beans may be a separate machine or may be comprised in a machine for producing a coffee-based beverage. Such machines are also referred to simply as "coffee grinders", "coffee grinders" or "mills". More particularly, the present invention relates to a coffee grinder arranged to provide a dose of suitably layered ground coffee.

Background

As is known, to prepare espresso coffee, a quantity (usually called "dose") of ground coffee is used. A dose may be a single dose, a double dose, or multiple doses. The dose of ground coffee is loaded into a filter basket, which is generally in the shape of a cup that is open at the top and has micropores at its bottom. Usually, a dose of coffee is pressed inside the filter basket so as to form a coffee powder disc. The filter is in turn supported by a movable filter (portafilter) arranged to be removably engaged inside a dispensing unit of the espresso coffee machine. Espresso coffee is obtained by passing hot water under pressure through a coffee powder disc.

The coffee powder is obtained using a coffee grinder. In known coffee grinders, coffee beans are ground by passing them through a grinding member. Flat, conical or cylindrical types of grinding members are known. Typically, the grinding member of a coffee grinder comprises a stationary member and a member that rotates relative to the stationary member. For example, in a coffee grinder with a conical grinder, one grinder is stationary while the other grinder is rotated by a motor. Some coffee grinders are capable of varying the distance between the grinders in order to vary the particle size of the ground coffee.

US2016/220067a1 discloses a variable speed coffee grinder.

EP2810592a1 discloses a coffee grinder, in particular for an automatic coffee machine.

WO2017/055433a1 discloses a coffee grinder with variable speed.

DE3503011a1 discloses a device for setting the spacing of the grinding bodies of a particle mill.

CN107692874A discloses a rotational speed regulation speed of a grinding device.

Disclosure of Invention

The applicant carried out experiments relating to grinding coffee powder. For the purposes of the present invention, ground coffee powder is considered to be formed substantially of particles or grains having the theoretical characteristic size. This theoretical characteristic dimension will also be referred to by the term "equivalent diameter" in the following of the present description. Also, the abbreviation term "ground product" may be used as an alternative to the more complete term "ground coffee powder" or other similar expressions.

The applicant has perceived that all known coffee grinders, regardless of the manufacturer or of the type of grinding member or of the specific mechanism used, produce ground products containing particles that vary greatly in size from one another. The range of equivalent diameters covers three orders of magnitude, from a few micrometers to over one millimeter.

The relatively large number of particles may be expressed as a special distribution called "particle size distribution" or "particle size curve" which has a development curve similar to that shown in fig. 1 (regardless of the coffee grinder used).

The curve representing the particle size distribution is called bimodal distribution. The high peak (on the right) is referred to as the "first mode", and the low peak (on the left) is referred to as the "second mode".

As mentioned above, the purpose of ground coffee is to be used in an espresso coffee machine for dispensing a coffee beverage.

It is clear that a particle size with a greater amount of fine particles results in a smaller water flow, and therefore the coffee is "shorter" (compared to a particle size with a greater amount of large particles) in the same dispensing time.

Typically, each brewer suitably adjusts his/her coffee grinder to obtain a particle size that appears to him/her to produce the best beverage.

Whether the machine has a flat grinder, a conical grinder or a cylindrical grinder, the smaller the distance between the grinding members, the greater the number of fine particles and the smaller the number of large particles. The opposite will be true for larger distances between the abrasive elements (i.e., the fewer the number of fine particles, the greater the number of large particles).

Typically, the brewer adjusts the grind settings whenever the coffee beans charged into the hopper before grinding are changed. The variation in coffee may be due to the use of different brands or different packages of the same brand.

The applicant has identified the object of reducing the sensitivity of the coffee grinder to variations in the coffee to be ground.

Another object identified by the applicant is to provide a coffee grinder which is able to suitably modify the organoleptic characteristics of the espresso coffee obtained by grinding the product.

According to the applicant, the above mentioned objects are achieved by a coffee grinder capable of varying the particle size profile when grinding a dose of coffee.

US2016/220067A1 states at [0019] that a coffee grinder with a variable speed motor is capable of grinding finely ground coffee more accurately and consistently at a lower speed than a conventional high speed grinder. Different methods of brewing coffee (e.g., espresso) require cutting coffee beans into uniform particles that are uniformly distributed. Existing coffee grinders that rotate at high speeds tend to crush the coffee beans rather than cut them, especially when the motor is activated, resulting in inconsistent particle sizes.

US2016/220067a1 discloses a coffee grinder using a variable speed motor whose speed and starting torque characteristics can be adjusted by a programmable controller to accommodate various coffee preparation methods or coffee bean types, while maintaining the ability to grind at high speeds when precision is not required.

Contrary to the teaching, the object of the present invention is to provide a dose of ground coffee directly in the filter basket with different layers having different average sizes.

According to a first aspect, there is provided a coffee grinder for grinding coffee beans and forming a dose of ground coffee in a filter basket, wherein the ground coffee has a bottom layer of ground coffee having a first average particle size and an adjacent layer of ground coffee having a second average particle size, the coffee grinder comprising:

-a grinding member for grinding coffee beans;

-an electric motor for rotating at least one grinding member relative to another grinding member; and

-means arranged to vary the rotational speed of the electric motor between a first speed and a second speed during grinding of coffee beans for forming a dose,

wherein the content of the first and second substances,

the second average particle size is less than the first average particle size and the first velocity is greater than the second velocity, or

The second average particle size is greater than the first average particle size, and the first velocity is lower than the second velocity.

An adjacent layer is a layer adjacent to and on top of the first layer. The first layer is produced first (so that the ground coffee is substantially at the bottom of the filter basket) and the adjacent layer is produced directly after the first layer so that the respective ground coffee rests on the first layer. One or more layers can be provided on adjacent layers, wherein the one or more layers have ground coffee particles having an average size that is different from an average size of ground coffee in the adjacent layer.

According to an embodiment, the coffee grinder further comprises a rotation counter for counting the number of rotations of the grinding member relative to the further grinding member, wherein the speed variation means are arranged to vary the speed from a first speed to a second speed depending on a set number of relative rotations of the grinding member and the further grinding member.

The set number of relative rotations can be any number (integer or decimal). Preferably, the set number of relative rotations is calculated as a function of the total set time for grinding a dose or as a function of the total number of rotations for grinding a dose. It is further preferred that the set number of relative rotations is calculated as a function of the total number of layers in the dose.

It should be noted that the first speed is the speed that the motor reaches after a threshold number of revolutions, which is counted from the start of the motor. The number of rotations may be set to any number between about 0.5 and about 3.0 (e.g., about 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0).

For example, when the threshold rotation number is set to 1.0, the total rotation number is set to 5, and the total number of layers is 2, the set number of relative rotations may be 2. In other words, a first speed is reached in a first revolution, which maintains two revolutions, and then a second speed is maintained for the remaining two revolutions. However, the grinding can also be arranged such that the number of revolutions for the first layer differs from the number of revolutions for the first layer. More than two layers can be provided.

According to an embodiment, the coffee grinder further comprises a timer, wherein the speed variation means is arranged to vary the speed from the first speed to the second speed according to a set time period counted from the start of the electric motor.

The set time period can be calculated as a function of the total set time for grinding a dose. It is further preferred that the set period of time can be calculated as a function of the total number of layers in the dose.

Preferably a threshold time is considered. The threshold time is the time from the motor starting to reaching the first speed. The threshold time can be a fraction of the total time for milling a dose. According to an embodiment, the threshold time can be between about 1/7 and about 1/4 of the total time to grind a dose. For example, the threshold time can be between about 1/6 and about 1/5 of the total time to grind a dose. When the total time is about 6 seconds, the threshold time can be between about 1 second and about 1.2 seconds.

For example, when the total time is 6 seconds, the threshold time is 1 second, and the total number of layers is 2, the change from the first speed to the second speed can be performed after 3.5 seconds from the start of the motor.

According to an embodiment, the coffee grinder further comprises a weighing component for calculating the mass of the dose of ground coffee, wherein the speed variation means is arranged to vary the speed from a first speed to a second speed depending on the mass of the first part of the dose of ground coffee at said first speed.

Also in this example, it is preferred to consider the threshold and calculate the quality of the coffee dose after a threshold time or a threshold number of revolutions. The threshold time can be a fraction of the total time for milling a dose, as described above. The threshold number of rotations can be a fraction of the total number of rotations used to grind a dose, as described above.

The speed change means can be arranged to change the speed of the electric motor step by step or continuously.

According to an embodiment, the coffee grinder further comprises an interface for selecting a speed profile for grinding a dose of coffee.

According to an embodiment, the coffee grinder further comprises an encoder for detecting the rotational speed of the electric motor.

According to a second aspect, the invention provides a method of grinding coffee beans to obtain a dose of ground coffee in a filter basket, the ground coffee having a bottom layer of ground coffee having a first average particle size and an adjacent layer of ground coffee having a second average particle size, the method comprising:

(a) providing a grinding member for grinding coffee beans;

(b) providing an electric motor for rotating one abrasive component relative to another abrasive component; and

(c) rotating the at least one grinding member relative to another grinding member at a first speed and then at a second speed during grinding,

wherein

The second average particle size is less than the first average particle size and the first velocity is greater than the second velocity; or

The second average particle size is greater than the first average particle size, and the first velocity is lower than the second velocity.

According to an embodiment, the invention further comprises: counting the number of rotations of the grinding member relative to the other grinding member; and varying the speed from a first speed to a second speed in accordance with a set number of relative rotations of the grinding member and the further grinding member.

According to an embodiment, the invention further comprises changing the speed from the first speed to the second speed according to a set time period counted from the start of the electric motor start.

According to an embodiment, the invention further comprises varying the speed from a first speed to a second speed in dependence on the mass of the first portion of the dose of coffee ground at said first speed.

Said speed change from the first start-up speed to the second speed can be performed continuously or stepwise.

According to an embodiment, instead of the means being arranged to vary the rotational speed of the electric motor between the first speed and the second speed during grinding of the coffee beans for forming the dose, an actuator may be provided which is arranged to vary the distance between one grinding member and the other grinding member during grinding of the coffee beans for obtaining the dose of ground coffee.

The actuator may be arranged to vary the distance between the grinders continuously or stepwise during grinding of the coffee beans to obtain the dose of ground coffee.

The distance between the grinders can vary during grinding of a dose from at least a first distance to at least a second distance, wherein said first distance is smaller than said second distance, so as to obtain at least a first portion of a dose of ground coffee having a first particle size and a second portion of a dose of ground coffee having a second particle size.

Preferably, the coffee grinder may further comprise an interface for selecting a speed profile or a distance profile for grinding a dose of coffee.

Preferably, the coffee grinder may further comprise an encoder for detecting the rotational speed of the electric motor.

According to another aspect, instead of varying the rotation speed of the electric motor during grinding of the coffee beans in order to obtain the dose of ground coffee, the distance between the grinding members is varied during grinding of the coffee beans in order to obtain the dose of ground coffee.

During the grinding of the coffee beans to obtain the dose of ground coffee, the distance between the grinders may be varied continuously or stepwise.

The distance between the grinders can vary during grinding of a dose from at least a first distance to at least a second distance, wherein said first distance is smaller than said second distance, so as to obtain at least a first portion of a dose of ground coffee having a first particle size and a second portion of a dose of ground coffee having a second particle size.

Drawings

The following detailed description of the present invention is provided by way of non-limiting example and is read with reference to the accompanying drawings, in which:

figure 1 is a graph showing an example of a particle size distribution expressed on a logarithmic scale;

figure 2a shows a schematic view of a dose of ground coffee with a standard particle size distribution obtained in a filter basket inserted inside a mobile filter;

figure 2b shows a schematic view of a dose of ground coffee obtained in a filter basket inserted inside a mobile filter, with a particle size distribution varying according to the invention;

FIG. 3 shows a graph of two particle size distributions on a linear scale obtained at two different grinding speeds;

FIG. 4 is a graph on a linear scale of two particle size distributions, the first particle size distribution being obtained at a constant speed and the second particle size distribution being obtained by combining the abrasive products resulting from two different speeds;

FIG. 5 is a schematic view of a coffee grinder according to an embodiment of the invention; and

figure 6 is a view of some parts of the machine according to figure 5.

Detailed Description

Fig. 1, which has been briefly described above, is a graph showing an example of the particle size distribution of a dose of coffee powder. The curve representing the particle size distribution is called bimodal distribution. The high peak (on the right, associated with larger size particles) is referred to as the "first mode", while the low peak (on the left, associated with smaller size particles) is referred to as the "second mode".

The applicant has studied and surprisingly found that a coffee grinder capable of varying the particle size curve in order to increase the bell-shaped amplitude corresponding to the first mode (higher peak on the right side of fig. 1) reduces the sensitivity of the coffee grinder. In other words, increasing the amplitude of the first mode reduces the need to adjust the particle size as the coffee in the hopper changes.

The applicant has carried out further studies and has surprisingly found that arranging the ground product inside the filter basket in a suitable manner can further reduce this sensitivity. In particular, it has been shown that better performance is obtained by arranging larger particles at the bottom and finer particles at the top.

The applicant has perceived that a coffee grinder capable of modifying the particle size profile during grinding of a dose can reduce the sensitivity of the coffee grinder and achieve two objectives.

According to a first embodiment of the invention, the coffee grinder comprises a grinding member, the distance of which is adjustable and varies during grinding of a dose. Preferably, the distance between the grinding members can be adjusted electrically by means of an actuator (e.g. an electric motor or a linear actuator, such as a piston 8) and a suitable control circuit.

With the coffee grinder according to the first embodiment, grinding of a dose D can be performed by varying (stepwise or continuously) the distance between the grinding members (during grinding of a dose) in order to obtain a ground product having a first, wider modality. It was found in practice that the first mode moves towards finer particles when the distance between the grinders is reduced, and towards larger particles when the distance is increased.

Thus, for example, a coffee grinder (which utilizes a greater distance between the grinders to produce a first portion of the dose of powder and a smaller distance between the grinders to produce the remaining portion) will generally produce a ground product having a wider bell-shape of the first modality. Thus, in general, starting at a certain distance between the grinders and reducing this distance during grinding of a dose, a ground product with a wider bell-shape of the first modality will be obtained.

The variation of the distance between the grinders during grinding of a dose F can be continuous or gradual. By means of the coffee grinder according to the first embodiment it is also possible to provide, for example, a first layer grinding product using a larger distance (in order to obtain larger particles) and a second layer using a smaller distance (in order to obtain finer particles). Obviously, more than two layers can be obtained, or, as mentioned above, a continuous variation (single, double or multiple) can be obtained by continuously varying the distance between the grinders during the grinding of a dose D.

The dose D shown in the figure is obtained by grinding coffee beans without changing the distance between the grinders. In fig. 2a, the distribution of the abrasive product inside the filter is random and not controlled.

In fig. 2b, the distribution inside the filter is suitably controlled using the coffee maker according to the invention. In particular, the bottom layer is characterized by an average larger particle, while the top layer is characterized by an average smaller particle. The bottom layer is obtained by keeping the grinder at a greater distance (compared to the distance at which the grinder is located in the second part of the dose grinding operation), in which the top layer is obtained with an average finer grain.

According to another embodiment of the invention, the coffee grinder is arranged to change the particle size during grinding of a dose by a change in the relative rotational speed of the grinding member. The expression "relative rotation" is understood to mean the rotation of one part with respect to the other. Typically, one abrasive member remains stationary while the other abrasive member rotates.

Figure 3 shows the effect of the speed of rotation of the grinder on the particle size. In particular, fig. 3 shows two particle size curves obtained by maintaining a constant distance between the grinders and by varying the speed of rotation. Unlike fig. 1, the curve in fig. 3 is a linear scale in order to highlight the difference in the first mode.

It can be seen that at lower speeds, the first modality moves to the left and its relative amount decreases (relative to the advantage of the second modality).

At higher speeds, the first mode moves to the right and increases its relative amount.

The variation in speed is preferably obtained by means of a suitable electronic speed regulator for the electric motor. Many devices of this type, which vary according to the type of motor used, are available on the market. According to an embodiment of the invention, the coffee grinder comprises a three-phase asynchronous electric motor and an inverter for speed control or any known frequency modulator.

According to an embodiment of the invention, the coffee grinder performs a dose grinding at a variable speed (stepwise and/or continuous) in order to obtain a dose of ground product having a first modality that is wider than normal.

In fact, according to the above, the first mode moves to the left when the rotation speed is reduced, and moves to the right when the rotation speed is increased. Thus, for example, a coffee grinder according to the invention may be arranged to provide a portion of a powder dose at a higher speed and another portion of a powder dose at a lower speed. The overall so obtained dose will include a wider bell shaped abrasive product of the first mode.

Fig. 4 is a graph showing a comparison of two particle size curves. In particular, the graph shows a first particle size curve (dashed line) obtained at a single velocity and a second particle size curve obtained at two velocities. The particle size curve obtained by combining powders obtained by performing two grinding operations at different speeds represents a greater dispersion (greater standard deviation) than the curve obtained by performing at constant speed, which curve results in the same total head loss.

According to the invention, it is preferable, for example, to be able to produce the first (bottom) layer of abrasive product at a higher speed in order to obtain larger particles and the second (top) layer at a lower speed in order to obtain finer particles. Particles belonging to the solid curve shown in fig. 3 will be deposited in the first layer, while particles belonging to the dashed curve will be deposited in the second layer. Obviously, more than two layers can be obtained, or a continuous variation can also be obtained by continuously varying the speed.

According to the applicant, an increase in the amplitude of the bell shape corresponding to the first mode modifies the organoleptic aspect of the beverage. As is known, in practice, the particle size distribution determines the amount of beverage dispensed for the same dispensing time and flow rate. In fact, the coffee powder causes a "head loss" or a "pressure drop", which determines the flow rate of the beverage.

According to the invention, it is possible to exceed the limits of known coffee grinders and to produce more particle size curves at the same head loss. For example, the two curves shown in fig. 4 are characterized by two different amplitudes of the bell shape of the first mode shape.

This means that, although the two curves shown in fig. 4 result in the same infusion time, the different sizes of the particles result in different contact areas between the water and the coffee powder and therefore in different solubilities.

The choice of particle stratification changes the total load loss. Arranging the two curves shown in figure 3 in reverse order will result in two different head losses and thus two different beverages. The mode of wetting of the coffee powder inside the filter also results in different drainage during the extraction cycle.

Fig. 5 shows, in a very schematic form, the main components of a coffee grinder 1 according to an embodiment of the invention: 2 denotes an electric motor for the relative rotation of the grinder 3 or for moving the grinder 3; 4 an inverter for controlling the speed of the motor; 5 denotes a control unit; and 6 an encoder (optional) for detecting the speed.

Fig. 5 also shows in schematic form the passage followed by the coffee to be ground up to the filter basket FT housed inside the movable filter PF.

According to an embodiment, the variation of the speed/distance of the grinder may be performed by the brewer through a suitable interface 7 (fig. 6). The interface 7 can comprise, for example, a button (or buttons) for selecting a predetermined rotation speed, a predetermined distance between the grinders, a rotation speed profile and a distance profile between the grinders. The interface may alternatively comprise a rotatable knob for selecting (continuously or stepwise) a plurality of rotational speeds (or distances between grinders), or a touch screen for selecting from a plurality of options/speeds available. The interface 7 is connected (directly or by other means, such as a CPU 5) to an inverter 4, which inverter 4 is used to vary the power frequency of the motor and thus the speed of the motor. Preferably, an option can be provided to select a rotational speed from rotational speeds provided by the manufacturer or a user selected speed. Preferably, a memory for storing rotational speed values and/or speed profiles can be provided for grinding a dose (single, double or multiple) not at a constant speed, but at two (or more) different speeds or at continuously varying speeds.

Thus, the control unit 5 transmits the rotation speed for the motor 2 to the inverter 4. The system can operate in open loop, i.e. without measuring the actual rotational speed of the motor, or in closed loop, i.e. by detecting the speed of the motor using a dedicated device, such as the encoder 6.