EP1981639B1 - Ball mill with an adjustable compensating mass - Google Patents

Description

The invention relates to a ball mill with adjustable balancing mass, in particular a planetary or centrifugal ball mill on a laboratory scale according to the definition of claim 1 and a method for operating them according to claim 15.

Lab scale ball mills are used for a wide range of applications, in particular for crushing and mixing samples and for mechanical alloying. An overview of common laboratory mills can be found on the applicant's website at www.fritsch.de.

In planetary and centrifugal ball mills grinding bowls are arranged eccentrically to a center axis and move on a circular orbit about the center axis. As a result of the rotation of the grinding bowls, a centrifugal force directed radially outwards is exerted on the grinding stock.

In a centrifugal ball mill, the rotation of the grinding bowl about its own axis with respect to the laboratory system is prevented. In contrast, planetary ball mills are based on creating a combined orbital and rotational motion for the grinding bowls by additional rotation about the grinding bowl axis in the laboratory system.

Unlike a centrifugal ball mill, the drive of the grinding bowls in a planetary ball mill thus causes an absolute rotational movement of the grinding bowl around its own axis, the recording or planetary axis, so that in a planetary ball mill in comparison to a centrifugal ball mill, a significantly larger, further centrifugal component is generated. This is superimposed on the centrifugal component, which is generated by the circulation of the grinding bowls about the center axis. Finally, the Coriolis effect is also effective. These three forces result in the planetary ball mill a resulting force field to which the grinding balls and the ground material are exposed.

With certain dimensions of the rotating parts and certain rotational speeds trajectories for the grinding balls are generated in a planetary ball mill. The grinding balls then move across the grinding bowl until they impinge on the inner wall of the grinding bowl. Thereafter, the grinding balls are taken along the inner circumference of the grinding bowl until the resulting force again ensures that the above-described transverse movement takes place and grinding balls perform a flight movement through the grinding bowl. This is also referred to as "Wurfregime". Unlike a centrifugal ball mill, a planetary ball mill can achieve a significantly better grinding effect at higher speeds.

The forces occurring due to the rotational movements of the various components, in particular in a planetary ball mill can be relatively high, so that the mills must be well balanced. In a centrifugal ball mill this problem is not so serious, so that older centrifugal ball mills could be operated even without or with a fixed balance weight. In laboratory planetary ball mills occur due to the possibility of high speeds to drive, however, particularly large imbalances or forces. Therefore, the said Laboratory planetary ball mills for decades only with a symmetrical arrangement of several grinding stations, such as two or four, built. Nevertheless, a few years ago, the construction of a laboratory planetary ball mill with only a single grinding station and leveling compound, which was described in the patent DE 197 12 905 C2 which is hereby fully made by reference to the subject matter of the present disclosure. Such a laboratory planetary ball mill is also referred to as a mono-ball mill or more precisely as a planetary mono (ball) mill and is sold under the brand name "pulverisette® 6" (see www.fritsch.de).

The pulverisette® 6 is a planetary monobloc mill with a displaceable balancing mass that compensates for the moment of inertia of a single grinding station. Although this mill has proven itself, it can still be improved.

To operate the mill, the user typically looks in a table in the operating instructions for the desired position of the leveling compound for a particular grinding vessel or weighs this and sets the target position before starting the mill by hand with a knurled nut. At first, this type of setting is relatively cumbersome and not very comfortable.

There is also the possibility that the mill can be operated with completely wrong adjustment of the balancing mass, which corresponds to a large imbalance. This results in strong vibrations and could even lead to damage to the mill or even prevent grinding altogether, since safety mechanisms stop the operation.

But even if the adjustment is done correctly, it is relatively inaccurate. An inaccuracy factor is e.g. the treatment according to the total mass of the filled grinding vessel. That no distinction is made between e.g. a grind jar with a net mass of 1 kg with a filling of 2 kg and a grinding jar with a net mass of 2 kg with a filling of 1 kg. So there are already inaccuracies in the determination of the actual adjustment size. Furthermore, the approach can not take dynamic effects into account. For example, This unique setting can not take into account the fact that the vibrations become stronger with increasing speed. Therefore, at high speeds undesirable vibrations may occur despite proper adjustment. A change of the ground material during the grinding process can not be considered at all.

Therefore, it is an object of the present invention to provide a ball mill which is comfortable to operate and offers high reliability.

Yet another object of the invention is to provide a ball mill, which has a very high smoothness, especially at high speeds.

Another object is to provide a method of operating such a ball mill.

The object is solved by the subject matter of the independent claims. Further developments are defined in the subclaims.

It can be seen that the use of an adjustable balancing mass for a mono-ball mill with only a single grinding station is of particular importance in order to compensate for the moment of inertia of this one grinding station. However, it is also within the scope of the invention to use an adjustable balancing mass for (fine) control of imbalance in a ball mill with multiple symmetrical grinding stations, for example, to compensate for the moment of inertia of different grinding bowl and / or fillings in the grinding stations and to further improve their smoothness , The following describes the preferred case of the mono-ball mill.

Preferably, therefore, a mono-ball mill is provided, in particular a planetary or centrifugal ball mill on a laboratory scale, with a housing, a carrier device, a single grinding station, one drive for the carrier device and the grinding station, arranged on the support device mass balancing device with a balancing mass and an adjusting device for at least radial adjustment of the balancing mass to change the moment of inertia adapted to the - respective, the grinding vessel and the filling dependent - moment of inertia of the grinding station, or to compensate for the moment of inertia. The carrier device rotates during operation of the mill relative to the housing or in the laboratory system about a center axis. The grinding station comprises a grinding bowl receiving device for at least one grinding jar, is mounted rotatably about a center axis with respect to the axis of the receiving shaft to the carrier device and is carried by the latter about the center axis. The drive of the carrier device and the receiving device is preferably carried out in opposite directions, for example by means of coupled belt drives by a single overall drive motor.

Furthermore, during operation, the grinding station comprises at least one grinding jar filled with ground material and grinding balls and inserted into the receiving device. The term "milling balls" is also meant to include non-spherical media as known in the art. The grinding jar is held in the receiving device as it is inserted and secured in the receiving device to operate the mill. Instead of a grinding jar, several grinding jars can be stacked one above the other in the one receiving device. In any case, a mono-ball mill has no further rotating grinding station, opposite a grinding station to compensate for the imbalance. Instead, with respect to the center axis with respect to the receiving device, the mass balancing device is arranged with the balancing mass to form a moment of inertia for the one grinding station. With this arrangement, a cost-effective and particularly compact design of the ball mill can be realized. In particular, unlike a mill with several grinding stations can even be achieved that the receiving device, possibly even the grinding vessel, to reach beyond the center axis or mass balance level. According to the invention, the mono-ball mill has a controllable from outside the carrier device motor drive for the adjusting device, with which during the rotation of the carrier device, the balancing mass can be adjusted.

This is highly advantageous because a manual adjustment can be omitted and the mill is suitable for assembly with an automatic control loop, so that the user does not have to worry about the adjustment of the balancing compound no matter which grinding vessel is used or how difficult the filling is. Furthermore, the mill offers the Possibility of a successive speed-dependent adjustment or adaptation.

For this purpose, the ball mill preferably also comprises a measuring device for measuring the dynamic imbalance and a control device which controls the drive of the adjusting device in dependence on the measured unbalance to automatically adjust the moment of inertia by means of the radial displacement of the balancing mass to the moment of inertia of the grinding station more precisely, in order to compensate for the respective moment of inertia of different grinding vessels and / or different fillings of the grinding vessels. Advantageously, a control loop can thus be constructed which even takes dynamic effects into account. The mass and the displacement path of the leveling compound are in particular adapted to the grinding station with any grinding vessels in the range of preferably 80 ml to 500 ml, e.g. made of stainless steel and / or agate, plus the filling, consisting of regrind and grinding balls or grinding media.

A particularly great advantage of the invention lies in the fact that with increasing speed by itself ever smaller imbalance-generating effects can be measured, since the vibration-causing forces increase at constant moment of inertia with the speed. As a result, the sensitivity of the control is inherently speed-dependent, so that the faster the mill turns, the more accurate can be readjusted and so the mill can still be operated with low vibration, even at high speeds.

For the laboratory ball mill according to the invention, the use of an acceleration sensor has proved to be useful to measure the imbalance. Of the Acceleration sensor is preferably fixed to the non-rotating suspension of the support device, for example attached to a suspension plate of the housing below the support device and thus measures the acceleration caused by the vibration suspension of the suspension during operation, ie during rotation of the support device, in particular the size and / or direction of acceleration ,

If the direction of the imbalance is to be determined, the mill preferably has means for detecting the angular position of the carrier device during the rotation about the center axis. For this purpose, a magnet arrangement with magnets on the carrier device, preferably on its underside, has proven to be expedient, which are detected by means of stationary Hall sensors, wherein the magnet arrangement has a e.g. has spatial coding to uniquely identify certain angular positions. For detecting the angular position of the carrier device, the signals of the Hall sensors are continuously evaluated by the control device during the rotation of the carrier device and the determined angular position is synchronized with the measurement result of the acceleration sensor. Thus, the controller can determine the direction in which the balancing mass must be moved to reduce the imbalance and not to increase.

Furthermore, an energy transmission device is provided which provides the energy for driving the adjusting device on the rotating carrier device. For this purpose, the energy transmission device has a fixedly attached to the housing first part and a co-rotating with the carrier device second part. Appropriately, the first and second part of Energy transmission device arranged coaxially to the center axis.

It has proved to be advantageous to transmit the adjustment energy mechanically to the rotating carrier device. According to a correspondingly preferred embodiment of the invention, the drive for the adjusting device comprises a drive shaft which is rotatably mounted in relation to the carrier device and which preferably extends coaxially within the center axis and is rotatably mounted therein. Accordingly, the center axis is formed as a hollow shaft, and the drive shaft protrudes with an upper and lower end of the hollow shaft. The upper end of the central drive shaft is mechanically coupled to the adjusting device via a gear, preferably by means of a belt drive. If the drive shaft is rotated relative to the carrier device, the belt drive transmits the movement or force to the adjusting device, more precisely a spindle drive, which finally shifts the balancing mass radially. The threaded spindle preferably extends through an internal thread in the substantially U-shaped balancing mass along its axis of symmetry.

According to a preferred embodiment, the drive shaft is free-running in the normal state with respect to the housing, so that the drive shaft is entrained by the carrier device due to the self-locking of the spindle drive of the adjusting device, that is, does not rotate relative to the carrier device. Thus, the self-locking of the adjustment prevents unwanted displacement of the balancing mass to the outside in spite of acting on the balancing mass centrifugal force.

To drive the adjusting device, the drive shaft is braked during rotation of the carrier device at a lower end relative to the housing, which causes a relative rotation to the carrier device and thus the drive of the adjusting device. In this case, braking in the laboratory system thus means driving in the co-rotated reference frame of the carrier device. Advantageously, thus by means of the braking device, the drive of the adjusting device of the fixed to the housing, i. non-co-rotating control device can be controlled. Preferably, a coupled to the lower end of the drive shaft magnetic brake is used with an anchor part and a flange as a braking device to brake the drive shaft.

It is advantageous to use the braking device in the normal state, i. in the case of the magnetic brake in the de-energized state, form free-running and to brake the drive shaft when current is applied. As a result, it can be prevented that the balancing mass changes inadvertently when e.g. the power is interrupted.

Particularly easy is the magnetic brake with only two states discontinuously controlled, d. H. The brake assumes either a free running or a fully braking condition.

According to an alternative embodiment, instead of the brake may be provided a separate drive motor for driving the drive shaft. Preferably, for this purpose, a servomotor is used, which is synchronized with the rotation of the carrier device to drive the drive shaft relative to the housing at the same speed as the carrier device in the normal state, ie, when the adjustment is not to be driven and to rotate so that the drive shaft does not rotate relative to the support device. To adjust the balancing mass is arranged in this embodiment by means of the drive motor of the stationary to the suspension, the drive shaft driven either at lower or higher speed than the carrier device, depending on the direction (in or out) the balancing mass to be adjusted.

Preferably, a first toothed belt wheel is attached to the upper end of the drive shaft, which is coupled via a drive belt with a second toothed belt wheel, which in turn is attached to the threaded spindle of the adjusting device. To impart the vertical rotation of the drive shaft in a horizontal rotation for the spindle drive, the drive timing belt is deflected at right angles, for example, under the inner stator of the mass balancing device. It can be seen that in this embodiment, the energy used for the displacement of the balancing mass is removed via the mechanical coupling to the carrier device whose rotational energy, when the balancing mass is moved inwardly against the centrifugal force. To move outward, only the self-locking of the spindle drive has to be overcome. That is, the controllable from outside the carrier device or motor drive the Verstelleinrichtng done indirectly by means of the total drive motor of the mill. It can be seen that for the purposes of this application under the name "motor drive" for the adjustment so also the braking of the drive shaft relative to the housing is to be understood, since then the drive - indirectly - motor and does not have to be adjusted by hand , This type of mechanical energy transfer has proven to be particularly useful in practice. However, it is conceivable that Adjustment energy in other ways, for example, contactless or contactless with an inductive energy transfer device to transfer to the rotating support device. For example, an axial coil pair could be attached to the housing and the support device to form a transformer or dynamo that transmits electrical energy. Alternatively, however, electrical slip rings, a hydraulic rotary coupling or the like could be used.

Accordingly, the invention provides a ball mill in which the imbalance during the rotation of the support device is measured and the balancing mass is adjusted in dependence of the measured imbalance to automatically controlled with the moment of inertia to compensate for the moment of inertia of the grinding station and to ensure a low-vibration running.

According to a preferred embodiment of the invention, the carrier device is accelerated to a setpoint speed and the unbalance is continuously measured during the acceleration, in particular regularly or continuously, and transmitted to the control device. Depending on the measured unbalance, the adjustment of the balancing mass is controlled, so that a control loop for adjusting the balancing weight is formed. The regulation takes place at least until the ball mill has reached the setpoint speed, since the imbalance increases with increasing speed, preferably even until the end of the grinding process. In other words, the moment of inertia is continuously regulated by means of the feedback signal of the measuring device to the control device at least during the startup of the ball mill. The measured unbalance is thus transmitted to the control device at least during the entire duration of the startup and evaluated to continuously control the adjustment of the balancing mass with increasing speed, wherein the readjustment of the counter-moment of inertia takes place stepwise or in several steps.

1. 1. Die Steuereinrichtung fährt die Mühle an und bestimmt, ob die Ausgleichsmasse in die richtige Richtung verstellt werden kann. Ist dies der Fall, wird die Ausgleichsmasse verstellt; ist dies nicht der Fall, wird die Trägervorrichtung automatisch angehalten und in umgekehrter Richtung wieder angetrieben, oder
2. 2. am Ende jedes Mahlvorgangs wird die Ausgleichsmasse in die jeweils anhand der Rotationsrichtung der Trägervorrichtung zugängliche Extremposition, d.h. entweder ganz nach innen oder ganz nach außen, bewegt und die Trägervorrichtung beim nächsten Anfahren in umgekehrter Richtung in Gang gesetzt. Mit diesem Verfahren kann sichergestellt werden, dass die Ausgleichsmasse immer in der "richtigen" Richtung verstellt werden kann.

The above-described drive with the brake allows the adjustment or displacement of the balancing mass with rotating support device only in one direction, which depends on the direction of rotation of the support device. That is, there is a structurally related fixed association between the direction of rotation of the support device and the displacement direction of the balancing mass. For example, in a concrete ball mill design, the balance mass can be displaced outwardly only when the support rotates clockwise and inwardly when the support rotates counterclockwise. That is, there is statistically only a 50% probability that the adjustment can be adjusted in the "right" direction. This places increased demands on the automatic regulation of the moment of inertia, which can be solved as follows:

1. 1. The controller drives the mill and determines whether the balancing mass can be adjusted in the right direction. If this is the case, the balancing mass is adjusted; if this is not the case, the carrier device is automatically stopped and driven in the reverse direction, or
2. 2. At the end of each grinding operation, the balancing mass is moved into the respective extreme position accessible on the basis of the direction of rotation of the carrier device, ie either completely inward or outward, and the carrier device is activated in the opposite direction during the next startup. With this Procedure can be ensured that the balancing mass can always be adjusted in the "right" direction.

It can be seen that the difficulty of the directional dependence when using a separate drive motor, instead of a braking device does not exist, since the drive of the drive shaft can then take place with rotating support device relative to this in both directions.

Further preferably, the control device comprises a storage means in which a predetermined tolerance interval for the imbalance is stored. The control device always sets the drive for the adjusting device in motion when the measured imbalance is outside the predetermined tolerance interval and activates the drive for the displacement of the balancing mass until the measured unbalance the associated limit of the tolerance interval whose amount is greater than the minimum achievable Imbalance, is reached. That When the mill is started up (in a control cycle), the tolerance interval in all steps is approached only from a single direction.

For some grinding tasks, it may be sufficient if the adjustment of the balance mass is not carried out during each grinding process. If this is desired, the control program gives the user the opportunity to temporarily disable the balancing mass adjustment.

In the following the invention will be explained in more detail by means of embodiments and with reference to the figures, wherein the features of different embodiments can be combined and regardless of whether they are disclosed in the specification, claims, figures or otherwise, they are also individually defined as essential components of the invention, even if described together with other features.

Brief description of the figures

Fig. 1

eine dreidimensionale Ansicht der _ Trägervorrichtung und des Antriebs einer erfindungsgemäßen Planeten-Mono-Kugelmühle von schräg oben,

Fig. 2

eine dreidimensionale Ansicht auf das Ausführungsbeispiel aus Fig. 1 von schräg unten,

Fig. 3

eine dreidimensionale Ansicht ähnlich Fig. 1, aber mit ausgeblendeter Aufnahmevorrichtung,

Fig. 4

eine dreidimensionale Ansicht ähnlich Fig. 3, aber aus anderem Blickwinkel und mit ausgeblendeter Ausgleichsmasse,

Fig. 5

eine Schnittdarstellung entlang der von der Planetenachse, Zentrumsachse und Ausgleichsmasse gebildeten Symmetrieebene der Trägervorrichtung,

Fig. 6

eine vergrößerte Darstellung eines Ausschnitts aus Fig. 5,

Fig. 7

eine dreidimensionale Ansicht auf das entlang der Symmetrieebene in Fig. 5 geschnittene Ausführungsbeispiel,

Fig. 8

eine schematische Aufsicht von unten auf die Trägervorrichtung,

Fig. 9

ein Blockschaltbild der Regelungskomponenten und

Fig. 10

ein Blockdiagramm des Steuerprogramms gemäß einem Ausführungsbeispiel.

Show it:

Fig. 1

a three-dimensional view of the _ carrier device and the drive of a planetary mono-ball mill according to the invention obliquely from above,

Fig. 2

a three-dimensional view of the embodiment Fig. 1 from diagonally below,

Fig. 3

similar to a three-dimensional view Fig. 1 but with hidden cradle,

Fig. 4

similar to a three-dimensional view Fig. 3 but from another point of view and with hidden balancing mass,

Fig. 5

a sectional view along the plane of symmetry formed by the planetary axis, center axis and balancing mass of the support device,

Fig. 6

an enlarged view of a section from Fig. 5 .

Fig. 7

a three-dimensional view on the along the plane of symmetry in Fig. 5 sectional embodiment,

Fig. 8

a schematic plan view from below of the support device,

Fig. 9

a block diagram of the control components and

Fig. 10

a block diagram of the control program according to an embodiment.

Detailed description of the invention

Fig. 1 shows a support device 2, which is rotatably mounted on a housing 1, of which only a suspension plate 12 is shown. The carrier device 2 is mounted eccentrically and turn rotatably a grinding station 3 with a Mahlgefäßaufnahmevorrichtung 32 for receiving a grinding vessel, not shown. The grinding jar is clamped or otherwise secured in the grinding jar receiving device 32 by suitable means. Opposite the grinding station 3, a mass balancing device 4 is arranged with radially displaceable balancing mass 42. The balancing mass 42 is formed substantially U-shaped with a central portion 422 and two obliquely to the central part extending legs 424 and 426.

Referring to Fig. 5 and 6 The carrier device 2 comprises two disc-shaped blocks 21, 22 bolted together. An overall drive motor (not shown) drives the lower disk-shaped block 22 via a V-belt 23 as a total drive. A center axis 24 is screwed at its lower with screws 14 fixed to the suspension plate 12 of the housing 1 and stored as a journal by means of a lower and upper ball bearing 25, 26 rotatably the support device 2. In the support device 2 by means of another ball bearing 33, the receiving or planetary shaft 34 rotatably supported in the carrier device 2.

The drive 5 for the grinding station 3 form a first toothed belt wheel 51, which is fastened between the ball bearings 25, 26 on the center axis 24, a second toothed belt wheel 52, which between the ball bearings 33 and a toothed belt 53, which couples the two toothed belt wheels 51 and 52 with each other such that the grinding station about the receiving axis or planetary axis 36 with a relative speed ratio of about k = -1.6 to - 2.2, preferably k = -1.7 to -2.0, ie opposite to the support device rotates.

The illustrated flying mounting of the Mahlgefäßaufnahmevorrichtung 32, the structure of the drive and the arrangement of the mass balancing device 4 on top of the support device 2 substantially corresponds to the mill, which in the DE 197 12 905 C2 described in particular in this regard by reference herein incorporated. However, it is apparent to those skilled in the art that the invention is not limited to this design, but also in a new, flatter design of planetary ball mills, as for example in the applications DE 20 2005 015896 . DE 20 2005 015897 and DE 20 2005 015898 filed by the same Applicant, filed on 7 October 2005, which are also incorporated herein by reference in their entirety.

Referring to FIGS. 5 and 7 hereinafter, the drive 6 of the mass balancing device 4 for the displacement of the balancing mass 42 (in FIGS. 5 and 7 not shown) explained in more detail. A drive shaft 61 is rotatably supported within the center axis 24 by means of a lower and upper bearing 62, 63, in this example two ball bearings. Accordingly, the center axis 24 is formed as a hollow axle. At the upper end 64 of the drive shaft 61, a toothed belt wheel 65 is attached, around which a toothed belt 66 is placed. The toothed belt 66 extends around the horizontal toothed belt pulley 65 in a horizontal plane, parallel to Level of the support device 2, and is by means of pulleys 71, 72, of which in Fig. 6 only the guide roller 72 is shown, deflected in the vertical. The drive shaft Zahnriemenrad 65 and the lower portion of the toothed belt 66 are recessed in a recess 27 in the top of the support device 2 to find space under the Mahlgefäßaufnahmevorrichtung 32. Above the pulleys 71, 72, the toothed belt is rotated by 90 ° in order to be able to drive a threaded spindle 74 via a toothed belt wheel 73. The threaded spindle 74 is mounted at its respective ends in an inner and outer stator 43, 44 and drives via an internal thread 75 in the balancing mass 42 to this (see. Fig. 3 ). In order to make an additional manual adjustment, a knurled knob 76 is still attached to the outer end of the threaded spindle 74, which is not needed in regular operation. The balancing mass is further radially guided between the inner and outer stator 43, 44 by means of guide rods 77, 78 and the threaded spindle 74 of the spindle drive (see. 3 and 4 ).

Again referring to FIGS. 5 and 7 At the lower end 67 of the drive shaft 61, a braking device in the form of a magnetic brake 8 is arranged. During operation, the carrier device or sun disk 2 now rotates about the sun axis 24 and at the same time drives the rotation of the planet shaft 34 and thus of the grinding station 3 via the drive 5. Although the rotation of the support device 2, a centrifugal force F acts on the balancing mass 42, which would like to pull it outward, but the threaded spindle 74 and the associated internal thread 75 of the balancing mass 42 are self-locking, so that the balancing mass despite rotation of the support device 2 is not automatically moved radially outward. As a result, by means of the belt drive 6 of the mass balancing device 4 the Drive shaft 61 taken with the rotation of the carrier device 2 and rotates with self-speed with, as long as the magnetic brake 8 runs free. That is, the drive shaft 61 rotates in the free-running state within the center axis 24 with the support device 2. In other words, the drive shaft 61 in the free-running state relative to the support device 2 at rest, that is, it finds no relative in this state Rotation instead, so that no drive on the threaded spindle 74 and the balancing mass 42 takes place.

To drive the threaded spindle 74 and to move the balancing mass 42 radially, the braking device 8 is activated during rotation of the carrier device 2, d. H. the brake is closed. Thereby, the drive shaft 61 is braked relative to the housing 1, whereby a rotation of the drive shaft 61 is effected relative to the rotating support device 2. By the relative rotation of the drive shaft 61 to the support device 2, the drive 6 of the mass balancing device 4 is set in motion, that the drive belt 66 is set in motion and the pulley 73, the threaded spindle 74 rotates. Thus, the balancing mass 42 is radial, d. H. either inwardly or outwardly, depending on the direction of rotation of the support device 2, moved. That is, by means of the proposed balancing mass drive 6, the energy or force which is expended to drive the balancing mass 42, the rotational energy of the support device 2 is removed.

The drive shaft 61 protrudes through a central opening 13 in the suspension plate 12 of the housing 1, and the braking device 8 is coaxially fixed from below to the suspension plate 12, which carries the center axis 24.

Referring to Fig. 6 the brake device 8 is formed as a magnetic brake with a fixed flange part 81 fixed to the suspension plate 12 and a co-rotating armature part 82 to which the drive shaft 61 is fixed. In the fixed relative to the housing 1 flange 81 a magnetic coil 83 is inserted, which brakes the armature part 82 under current application. For this purpose, a brake disc 85 is brought into overcoming an air gap 86 with a brake pad 87 in frictional engagement. In the illustrated embodiment, a magnetic brake of the company Magneta is used in Groß-Berkel with the type designation 14.110.103. Such magnetic brakes have braking forces with respect to the torque of 0.6 to 3.6 Nm.

It should be emphasized that the magnetic brake 8 is designed to be free-running in an inactivated or de-energized state and braking in an activated, current-charged state. This has the advantage that in case of power failure during operation of the mill no unwanted drive of the balancing mass is set in motion. Otherwise, the mill could be damaged. Instead of the magnetic brake and a servo motor may be provided.

Again referring to Fig. 1 and 5 is attached to the housing 1, more precisely to the suspension plate 12, a two-dimensionally measuring acceleration sensor 9. When the carrier device 2 rotates and the balancing mass 42 is not optimally adjusted, the carrier vibrates and transmits this vibration to the suspension 12. The acceleration sensor 9 measures the direction and magnitude in both dimensions (x and y directions) of the horizontal plane passing through Imbalance vibrations generated acceleration the suspension 12, illustrated by the arrows x and y. The measured acceleration vector rotates transversely to the center axis 24 and thus biases an acceleration ellipse whose magnitude represents a measure of the imbalance. The acceleration ellipse may be significantly eccentric due to differential stiffness in the two dimensions of the horizontal plane. Therefore, it is advantageous for the quality of the control signal to determine the magnitude of the acceleration along the first main axis of the ellipse and to use this as a parameter for the control of the adjustment of the balancing mass 42. Hereby, the adjusting device is preferably controlled as follows. The controller drives the mill and continuously measures the acceleration vector. Then, the balance mass is slightly displaced in an (arbitrary) direction, and the change in the magnitude of the acceleration ellipse along the first major axis is determined. If the size has decreased, this has been the "right" direction and the process continues until the tolerance interval is reached. If the size has increased, this has been the "wrong" direction and it must be adjusted in the opposite direction. In the illustrated embodiment, the direction of rotation of the carrier device 2 is reversed for this purpose.

This embodiment of the ball mill has an angle detection device 10, with which the angular position of the support device 2 during rotation can be determined. The angle detection device 10 comprises an arrangement of a plurality of magnets 101, which are fixed to the support device 2, more precisely to the underside thereof. The magnets 101 are annular, in this example on a plurality of circumferential lines 110, 112 arranged with different radii (see.

Fig. 8 ). A receiving device 102 with a plurality of Hall sensors 104 is arranged stationary relative to the housing 1 below the magnets 101. The magnets are arranged such that a coding is formed, so that by means of the corresponding Hall sensors 104 (here three) at least at one point of the support device 2- in Fig. 8 if this is left, where a second magnet 101 is disposed on the outer circumference 110, this angular position can be uniquely identified. For the remaining magnets 101, which at regular angular intervals on the inner circumference 112 on the support device 2, for example as in Fig. 8 shown schematically, in a uniform division of nine, are then sufficient to count the induced by the magnets 101 signals in the Hall sensor assembly 102nd

Referring to Fig. 9 is the angle detection device 10, more specifically, the Hall sensors 102 are read by a control device 103 and evaluated. Further, the controller 103 reads out the acceleration sensor 9 and synchronizes its data with the angle information. As a result, the control device 103 can even optionally determine in which direction the balancing mass 42 is to be displaced in order to reduce the imbalance. Furthermore, the control device 103 controls the braking device 8 in order to control the drive 6 of the mass balancing device 4 and the main drive 23 of the carrier device 2.

It can be seen that with the selected type of mechanical drive of the mass balancing device 4, the balancing mass 42 can always be displaced only in a certain direction, either inwards or outwards, depending on whether the carrier device 2 rotates clockwise or counterclockwise. Therefore persists random position of the balancing mass 42 only a 50% probability that the balancing mass 42 can be adjusted in a given direction of rotation of the support device 2 in the desired direction. This problem can eg with the in Fig. 10 illustrated exemplary control method can be solved with the following measures.

After the user input 202 to start the grinding process, the controller 103 loads 204 the tolerance interval from a memory means 105. Then, the controller 103 controls as follows:

In order to take account of the directional dependence of the drive 8, 61 of the adjusting device 74, 75, a direction initialization routine 206-212 is first executed. In this case, the ball mill is first approached 206 and carried out an initial measurement 208 of the acceleration ellipse. Subsequently, the adjustment drive for an initial adjustment 210 is started and the acceleration ellipse is measured 208 'again. Based on a comparison between the results 208 and 208 ', the control device 103 determines whether the leveling compound has been adjusted in step 210, the "correct" direction. Depending on the result of this initial measurement, the controller 103 then judges 211 either - if the direction was correct - to continue the mill up or, if the direction was wrong, to reverse the direction of rotation 212 and start up from the beginning at step 206. Both cases occur statistically at 50% each.

1. (a) Messen 213 der Unwucht,
2. (b) wenn die gemessene Unwucht außerhalb des Toleranzintervalls liegt (Abfrage 214), dann Verstellen 216 der Ausgleichsmasse 42 bis das Toleranzintervall errecht ist,
3. (c) Weiterbeschleunigen 219 der Trägervorrichtung 2 auf eine höhere Drehzahl,
4. (d) Messen 213 der Unwucht bei der höheren Drehzahl,
5. (e) wenn die gemessene Unwucht das Toleranzintervall verläßt (Abfrage 214), dann Verstellen 216 der Ausgleichsmasse 42 in derselben radialen Richtung wie bei Maßnahme (b) bis das Toleranzintervall wieder erreicht ist,
6. (f) Weiterbeschleunigen 219 der Trägervorrichtung 2 auf eine höhere Drehzahl.

If the direction is correct, after the direction initialization routine with a secondary routine 213-222, the carrier device 2 is started up as follows and the grinding operation is performed:

1. (a) measuring 213 of the imbalance,
2. (b) if the measured imbalance is outside the tolerance interval (query 214), then adjusting 216 the balancing mass 42 until the tolerance interval is reached,
3. (c) further accelerating 219 the carrier device 2 to a higher speed,
4. (d) measuring 213 the imbalance at the higher speed,
5. (e) when the measured imbalance leaves the tolerance interval (query 214), then adjusting 216 the balancing mass 42 in the same radial direction as in measure (b) until the tolerance interval is reached again,
6. (f) Accelerating 219 of the carrier device 2 to a higher speed.

The carrier device 2 is accelerated until the setpoint speed (query 218) is reached. After reaching the setpoint speed (query 218), the grinding process is continued for a long time and with further continuous measurement 213 of the imbalance and control 213, 214, 216 of the moment of inertia, until the grinding target is reached (query 222).

But it is also conceivable that balancing mass 42 at the end of each grinding operation in the inner or outer extreme position 42a, 42b (see. Fig. 8 ), depending on which adjustment direction is just possible due to the direction of rotation of the support device 2, and in the subsequent grinding process, the support device 2 in the opposite direction to set in motion. Thus, it can be ensured that the balancing mass 42 can always be adjusted in the right direction. It is only necessary to drive the carrier device 2 alternately clockwise and counterclockwise in successive grinding operations. With others Words is when braking the carrier device 2 after completion of a first grinding operation with a first rotational direction of the support device 2, the balancing mass 42 automatically adjusted to a first extreme position 42a or 42b. When the carrier device 2 is accelerated for a subsequent second grinding operation, the carrier device 2 is started in the reverse second direction of rotation. When braking the carrier device after completion of the second grinding operation, the leveling compound is then automatically adjusted to the opposite second extreme position 42b and 42a and when accelerating the carrier device 2 for a subsequent third grinding operation, the carrier device 2 is set in motion again in the first direction, etc.

It will be apparent to those skilled in the art that the above-described embodiments are to be understood by way of example, and that the invention is not limited thereto, but varied in many ways within the scope of the claims.

Claims (22)

1. Ball mill, in particular a laboratory-scale planetary ball mill or centrifugal ball mill, comprising a housing (1),
   a carrier device (2) which is mounted so as to be able to rotate relative to the housing (1) about a centre axis (24),
   at least one milling station (3) having a receiving device (32) for at least one milling vessel, which device is mounted so as to be able to rotate with respect to the carrier device (2) about a reception axis (36) and is entrained thereby about the centre axis (24), and having at least one milling vessel which can be filled with milling material and milling balls and can be inserted into the receiving device,
   a drive (23) for the carrier device (2),
   a drive (5) for the receiving device (32),
   an adjustable compensating mass (42) in order to form a counter moment of inertia for the milling station or the milling stations (3),
   an adjustment unit (74, 75) for adjusting the compensating mass (42) in order to change the counter moment of inertia to adapt it to the moment of inertia of the milling station or the milling stations (3),
   a drive (8, 61, 65, 66, 73) for the adjustment unit (74, 75), which drive can be controlled from outside the carrier device (2), in order to adjust the compensating mass (42) during rotation of the carrier device (2).
2. Ball mill as claimed in Claim 1, formed as a mono-ball mill having only a single milling station (3), wherein the adjustable compensating mass (42) is disposed opposite the one milling station (3) in relation to the centre spindle (24) in order to form a counter moment of inertia for the one milling station (3).
3. Ball mill as claimed in Claim 1 or 2, comprising
   a measuring unit (9) for measuring the unbalance, and a control unit (103) which controls the drive (8, 61, 65, 66, 73) of the adjustment unit in dependence upon the measured unbalance in order to automatically adapt the counter moment of inertia to the moment of inertia of the milling station or the milling stations (3) by means of adjusting the compensating mass (42).
4. Ball mill as claimed in Claim 3,
   wherein the control unit (103) comprises a storage means (105) storing a predetermined tolerance interval for the unbalance, wherein the unbalance measured by the measuring unit (9) is transferred to the control unit (103) as feedback and a control circuit is formed for adjusting the compensating mass (42), wherein the drive (8, 61, 65, 66, 73) for the adjustment unit is started up when the measured unbalance is outside the predetermined tolerance interval.
5. Ball mill as claimed in any one of the preceding Claims, further comprising an energy transfer unit (8, 61) for transferring adjustment energy to the rotating carrier device (2), wherein the energy transfer unit (8, 61) comprises a first part (81, 83) mounted in a stationary manner with respect to the housing and a second part (82, 61) which rotates simultaneously with the carrier device, and wherein the adjustment unit (74, 75) is driven by means of the transferred adjustment energy at least intermittently.
6. Ball mill as claimed in Claim 5,
   wherein the first and second parts (81, 83, 82, 61) of the energy transfer unit are disposed coaxially with respect to the centre aixs (24).
7. Ball mill as claimed in Claim 5 or 6,
   wherein the energy transfer unit mechanically transfers a control force or inductively transfers electrical adjustment energy to the simultaneously rotating second part (82, 61).
8. Ball mill as claimed in any one of the preceding Claims,
   wherein the energy used to adjust the compensating mass (42) in a motorised manner is drawn from the rotational energy of the carrier device (2).
9. Ball mill as claimed in any one of the preceding Claims,
   wherein the drive for the adjustment unit comprises a drive shaft (61) which is mounted so as to be able to rotate in relation to the carrier device (2) and is coupled to the adjustment unit (74, 75) by means of a gear mechanism (65, 66, 73) such that the compensating mass (42) is radially displaced when the drive shaft (61) is rotated relative to the carrier device (2).
10. Ball mill as claimed in Claim 9,
    wherein a braking unit (8) is provided for braking the rotation of the drive shaft (61) relative to the housing or a drive motor is provided for driving the driving shaft (61) in order thereby to effect a rotation of the drive shaft (61) relative to the rotating carrier device (2) and to drive the adjustment unit (74, 75), wherein the braking unit (8) comprises a magnetic brake (81-83),
    wherein the magnetic brake (81-83) is formed so as to be free-running in the absence of power and brakes the drive shaft (61) relative to the housing (1) upon being influenced with power.
11. Ball mill as claimed in any one of the preceding Claims,
    wherein the centre axis (24) is formed as a hollow spindle and the drive shaft (61) extends coaxially within the hollow spindle and having an upper and lower end (64, 67) which each protrude from the hollow spindle, wherein a drive wheel (65) is attached to the upper end and is coupled to the adjustment unit (74, 75) in order to drive the latter.
12. Ball mill as claimed in any one of the preceding Claims,
    wherein the adjustment unit (74, 75) comprises a spindle drive consisting of a threaded spindle and a corresponding internal thread for radially displacing the compensating mass (42) and the spindle drive is formed so as to be self-locking, wherein the spindle drive is driven by means of a drive shaft, mounted so as to be able to rotate in relation to the carrier device, when the drive shaft (61) is rotated relative to the carrier device (2).
13. Ball mill as claimed in any one of the preceding Claims,
    wherein the measuring unit (9) for measuring the unbalance comprises an acceleration sensor, wherein the acceleration sensor measures the direction and/or magnitude of the acceleration and/or the acceleration at least in two dimensions in a plane transverse to the centre axis (24) and the measuring unit (9) for measuring the unbalance is attached in a stationary manner with respect to the centre axis (24).
14. Ball mill as claimed in any one of the preceding Claims,
    wherein the mill comprises means (10) for detecting the angular position of the carrier device (2) during rotation about the centre axis (24), the measuring unit (9) is read out during rotation of the carrier device and is synchronised with the angular position in order to determine the direction of the unbalance.
15. Method for operating a planetary ball mill or centrifugal ball mill having at least one milling station (3) which in operation is entrained by a carrier device (2), rotating about a centre axis (24), about the centre axis (24) and simultaneously rotates about a reception axis (36) at least relative to the carrier device (2), and having an adjustable compensating mass (42) as a counter moment of inertia for the milling station or the milling stations (3), in particular for operating a ball mill as claimed in any one of the preceding Claims,
    wherein during rotation of the carrier device (2) the unbalance is measured, and
    the compensating mass (42), which is attached to the carrier device (2) in an adjustable manner, is adjusted in dependence upon the measured unbalance in order to automatically adapt the counter moment of inertia to the moment of inertia of the milling station or the milling stations (3).
16. Method as claimed in Claim 15,
    wherein the carrier device (2) is accelerated to a desired rotational speed and the unbalance is continuously measured during the acceleration, and
    wherein the adjustment of the compensating mass (42) is automatically controlled in dependence upon the measured unbalance, at least until the ball mill has reached the desired rotational speed.
17. Method as claimed in any one of the preceding Claims,
    wherein the carrier device (2) is accelerated to a desired rotational speed and the unbalance is continuously measured during the acceleration, wherein the compensating mass (42) is adjusted in a step-wise manner as the rotational speed increases and during the step-wise adjustment the compensating mass is adjusted a multiple number of times only in a single direction upon acceleration of the carrier device (2) until the measured unbalance is in a predetermined tolerance interval, and wherein the predetermined tolerance interval for the unbalance is stored in a storage means (105) and the unbalance measured by a measuring unit (9) is transferred to a control unit (103) as feedback so that a control circuit for adjusting the compensating mass is formed, wherein the control unit (103) then starts up a drive (8, 61, 65, 66, 73) for adjusting the compensating mass (42) in the direction which effects a reduction in the unbalance, when the measured unbalance is outside the predetermined tolerance interval.
18. Method as claimed in any one of the preceding Claims,
    wherein the radial direction of the adjustment of the compensating mass (42) depends upon the direction of rotation of the carrier device and the control unit (103) executes a control programme which automatically reverses the direction of rotation of the carrier device (2) when this is required in order to adjust the compensating mass (42) in the correct direction.
19. Method as claimed in any one of the preceding Claims,
    wherein the ball mill comprises a control unit (103) having a storage means (105) storing a predetermined tolerance interval for the unbalance, wherein at least the following steps are performed:

    (a) measuring (213) the unbalance,

    (b) if the measured unbalance is outside the tolerance interval, adjusting (216) the compensating mass (42) until the tolerance interval is reached,

    (c) accelerating (219) the carrier device (2) to a higher rotational speed,

    (d) measuring (213) the unbalance at the higher rotational speed,

    (e) if the measured unbalance exits the tolerance interval, adjusting (216) the compensating mass (42) until the tolerance interval is reached,

    (f) accelerating (219) the carrier device (2),
    wherein steps (d) to (f) are performed until a desired rotational speed is reached (218).
20. Method as claimed in Claim 19,
    wherein the radial direction of the adjustment of the compensating mass (42) depends upon the direction of rotation of the carrier device (2) and the control unit (103) determines whether

    (i) the direction of rotation of the carrier device (2) permits adjustment of the compensating mass (42) in the direction which reduces the unbalance, or

    (ii) the direction of rotation of the carrier device (2) does not permit adjustment of the compensating mass (42) in the direction which reduces the unbalance,
    and wherein the control unit (103) automatically makes the following decision (211) on the basis of the determined alternatives (i) or (ii):

    in the case of determined result (i), further accelerating the carrier device (2),

    in the case of determined result (ii), reversing (212) the direction of rotation of the carrier device (2).
21. Method as claimed in Claim 19,
    wherein the radial direction of the adjustment of the compensating mass (42) depends upon the direction of rotation of the carrier device (2),
    wherein the compensating mass (42) can be adjusted between first and second end positions (42a, 42b) which are radially opposite one another,
    wherein the compensating mass (42) is adjusted, upon completion of a milling process, into the first or second end position (42a, 42b) depending upon which adjustment direction is possible owing to the direction of rotation of the carrier device (2), and
    in the subsequent milling process the carrier device (2) is started up in the opposite direction in order to ensure that the compensating mass (42) can be adjusted in the correct direction so that the carrier device (2) is accelerated alternately in the clockwise and anti-clockwise directions in successive milling processes.
22. Method as claimed in any one of the preceding Claims,
    wherein the direction and magnitude of the acceleration of the suspension of the carrier device are continually measured in at least two dimensions in a plane transversely with respect to the centre axis (24) in order to determine the acceleration ellipse spanned by the acceleration vector rotating in the plane and to determine, using the change in the acceleration ellipse upon adjustment of the compensating mass, at least the accuracy of the direction of the adjustment.

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