Ball mill with automatically adjustable counterweight

Abstract

The invention relates to a ball mill, in particular a mono-planetary or mono-centrifugal ball mill on a laboratory scale, with a counterweight to provide a counter-moment of inertia for the grinding station or stations, wherein the counterweight can be adjusted by means of an adjustment device to change the counter-moment of inertia adapted to the moment of inertia of the grinding station or stations. According to the invention, the ball mill includes an automatic drive for the adjustment device, by means of which the direction of adjustment of the counterweight can be effected independently of the direction of rotation of the support device.

Description

Field of invention

[0001] The invention relates to a ball mill with an automatically adjustable counterweight, in particular a planetary or centrifugal ball mill on a laboratory scale with only a single grinding station (mono-ball mill). Background and general description of the invention

[0002] Laboratory-scale ball mills are used for a wide range of applications, especially for crushing and mixing samples and for mechanical alloying. The applicant has been manufacturing corresponding planetary ball mills on a laboratory scale for decades under the trademark pulverisette® (series 4 to 7) and they are described, for example, in DE 197 12 905, EP 1 945 364, DE 10 2006 047 481, EP 1 945 363, DE 10 2006 047 480, DE 10 2006 047 479, EP 1 933 984, EP 1 933 985, DE 10 2006 047 498, EP 2 010 329, EP 1 981 639 and DE 10 2010 044 254. An overview of the applicant's laboratory mills can also be found on its website at www.fritsch.de.

[0003] In planetary and centrifugal ball mills, grinding bowls are arranged eccentrically to a central axis and move in a circular path around this axis. The rotation of the grinding bowls exerts a radially outward centrifugal force on the material being ground.

[0004] In a centrifugal ball mill, the rotation of the grinding bowl around its own axis relative to the laboratory frame is prevented. In contrast, planetary ball mills are based on generating a combined circular and rotary motion for the grinding bowls by means of additional rotation around the grinding bowl axis within the laboratory frame.

[0005] Unlike a centrifugal ball mill, the drive of the grinding bowls in a planetary ball mill causes an absolute rotation of the grinding bowl around its own axis, the receiving or planetary axis. This results in an additional centrifugal force component being generated in a planetary ball mill compared to a centrifugal ball mill. This component is superimposed on the centrifugal force component generated by the rotation of the grinding bowls around the central axis. Finally, the Coriolis force also acts. These three forces combine to create a force field in the planetary ball mill, to which the grinding balls and the material being ground are subjected.

[0006] With specific dimensions of the rotating parts and specific rotational speeds, trajectories are generated for the grinding balls in a planetary ball mill. The grinding balls then move laterally through the grinding bowl until they strike its inner wall. Afterward, the grinding balls are carried along the inner circumference of the grinding bowl until the resulting force causes the lateral movement described above to occur again, and the grinding balls then perform a flying motion through the grinding bowl. This is also known as the "throwing regime." Unlike a centrifugal ball mill, a planetary ball mill can therefore achieve significantly better grinding results at higher rotational speeds.

[0007] The forces arising from the rotational movements of the various components, particularly in a planetary ball mill, can be relatively high, necessitating careful balancing of the mills. This problem is less critical in a centrifugal ball mill, allowing older models to be operated without a counterweight or with a fixed counterweight. However, laboratory planetary ball mills exhibit particularly large imbalances or forces. Therefore, for decades, these laboratory planetary ball mills were constructed using only a symmetrical arrangement of several grinding stations, e.g., two or four. Nevertheless, the applicant recently succeeded in constructing a laboratory planetary ball mill with only a single grinding station and counterweight, as described in patent DE 197 12 905 C2, which is hereby incorporated in its entirety by reference into the present disclosure.Such a laboratory planetary ball mill is also called a mono-ball mill or more precisely a planetary mono(ball) mill and is sold under the brand name "pulverisette". ® 6” distributed (see www.fritsch.de).

[0008] The pulverisette® 6 is a planetary monoball mill with a manually movable counterweight that compensates for the moment of inertia of the single grinding station.

[0009] A further development of the pulverisette® 6 is described in European patent EP 1 981 639 of the same applicant, in which the counterweight is adjusted automatically. While this design already represents an exceptionally sophisticated solution for the automatic adjustment of the counterweight, in the embodiment shown therein, the counterweight can only be adjusted in one direction for a specific direction of rotation of the support device. If this is the wrong direction (50% probability), the rotation of the support device must first be reversed before the counterweight can be adjusted in the correct direction.

[0010] This requires increased control effort and can extend the time required to adjust the counterweight. As a result, the grinding process can be delayed, and the ball mill will continue to operate with an imbalance for a longer period.

[0011] The present invention represents a further development and improvement of the ball mill described in European patent EP 1 981 639, which is therefore hereby incorporated by reference.

[0012] It is therefore an object of the present invention to provide a ball mill of the type mentioned at the outset in which the compensation of the imbalance is carried out quickly and precisely, so that the ball mill has the lowest possible imbalance during the grinding process, enables a high maximum speed and allows the grinding process to be started as quickly as possible.

[0013] A particular aspect of the object of the present invention is to provide a ball mill of the type mentioned above with a constructively elegant drive for the balancing mass to compensate for the imbalance.

[0014] The problem is solved by the subject matter of the independent claims. Further developments are defined in the dependent claims.

[0015] It is evident that the use of an adjustable counterweight is of particular importance for a mono-ball mill with only a single grinding station in order to compensate for the moment of inertia of this single grinding station. Therefore, the preferred case of the mono-ball mill is described below. However, it is also within the scope of the invention to use an adjustable counterweight for the (fine) control of the imbalance in a ball mill with several symmetrical grinding stations, for example, to compensate for the moment of inertia of different grinding bowls and / or fillings in the grinding stations and to further improve their smooth running.

[0016] According to the invention, a mono-ball mill, in particular a planetary or centrifugal ball mill on a laboratory scale, is provided, comprising a housing, a support device, preferably only a single grinding station, a drive for the support device and preferably the single grinding station, a mass balancing device arranged on the support device with a balancing mass, and an adjustment device for radially adjusting the balancing mass in order to change the counter-moment of inertia adapted to the respective moment of inertia of the grinding station – which depends on the grinding vessel and the filling – or to compensate for the moment of inertia. During operation of the mill, the support device rotates relative to the housing or, in the laboratory system, about a central axis.The grinding station comprises a grinding bowl receiving device for at least one grinding vessel, is rotatably mounted about a receiving axis eccentrically with respect to the central axis relative to the support device, and is guided by the support device about the central axis. The support device and the receiving device are preferably driven in opposite directions, e.g., by means of coupled belt drives by a single drive motor. Furthermore, in operation, the grinding station comprises at least one grinding vessel filled with material to be ground and grinding balls, which is inserted into the receiving device. The term "grinding balls" is intended to also include non-spherical grinding media, as known in the field. The grinding vessel is held in the receiving device when it is inserted and secured in the receiving device to operate the mill. Instead of one grinding vessel, several grinding vessels can also be stacked on top of each other in the single receiving device.In any case, a mono-ball mill does not have a second rotating grinding station opposite the one grinding station to compensate for its imbalance. Instead, the mass balancing device with its balancing mass is positioned opposite the mounting device with respect to the central axis to create a counter-moment of inertia for the single grinding station. This arrangement allows for a cost-effective and particularly compact ball mill design while maintaining high grinding capacity. In particular, unlike a mill with multiple grinding stations, it may even be possible for the mounting device, and potentially even the grinding vessel, to extend beyond the central axis or mass balancing plane.According to the invention, the mono ball mill has a motor-driven, in other words automatic, drive for the adjustment device that can be controlled from outside the carrier device, with which the counterweight can be automatically adjusted during the rotation of the carrier device.

[0017] This is highly advantageous because manual adjustment is eliminated, and the mill is suitable for integration with an automatic control loop, meaning the user no longer needs to worry about adjusting the counterweight, regardless of the grinding container used or its weight. Furthermore, the mill offers the possibility of gradual, speed-dependent adjustment, thus enabling particularly precise compensation for any imbalance.

[0018] According to the invention, the automatic drive for the adjustment device has a device for reversing the direction of rotation, so that the direction of adjustment of the counterweight can be effected independently of the direction of rotation of the support device, although the automatic drive of the adjustment device - without a separate motor of its own - is mechanically powered by the rotation of the support device relative to the housing or laboratory system, in other words, the drive energy for adjusting the counterweight is taken from the energy of the rotation of the support device.

[0019] This is particularly advantageous compared to the ball mill described in EP 1 981 639, since it eliminates the need to reverse the direction of rotation of the support device, regardless of the direction in which the support device rotates and regardless of the direction in which the counterweight must be adjusted to increase or decrease the moment of inertia. This allows for a significantly more elegant and faster compensation of the imbalance.

[0020] For control purposes, the ball mill preferably comprises a measuring device for measuring the dynamic imbalance and a control unit that automatically controls the drive of the adjustment device based on the measured imbalance. This allows the counter-moment of inertia to be automatically adjusted to the moment of inertia of the grinding station by means of the radial displacement of the counter-mass. More precisely, it compensates 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 established that even takes dynamic effects into account. The mass and displacement of the counter-mass are specifically 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 material to be ground and grinding balls or grinding media.

[0021] A particularly significant advantage of the invention lies in the fact that the imbalance-inducing effects, which become progressively smaller with increasing rotational speed, can be measured, since the vibration-causing forces increase with rotational speed at a constant moment of inertia. This makes the sensitivity of the control inherently speed-dependent, so that the faster the mill rotates, the more precise the adjustment can be, thus enabling low-vibration operation of the mill even at the highest speeds. Because the counterweight can be adjusted in both directions, if the point of minimum imbalance is exceeded during rotation without reversing the direction of rotation of the support device, the counterweight can be moved back in the opposite direction. This allows for very precise fine-tuning, especially due to the speed-dependent sensitivity of the imbalance compensation.

[0022] Advantageously, the reversal of the direction of rotation is effected by a gearbox with reversing of the direction of rotation, which allows for simple and very reliable control of the automatic drive for the adjustment device.

[0023] For the laboratory ball mill according to the invention, the use of an accelerometer has proven advantageous for measuring the imbalance. The accelerometer is preferably fixed to the non-rotating suspension of the support device, e.g., to a suspension plate of the housing below the support device, and thus measures the acceleration of the suspension caused by the vibration during operation, i.e., during the rotation of the support device, in particular the magnitude and / or direction of the acceleration. Furthermore, the accelerometer preferably measures the acceleration at least two-dimensionally in the plane transverse to the central axis.

[0024] To determine the direction of the imbalance, the ball mill preferably has means for detecting the angular position of the support device during rotation about the central axis. A magnetic arrangement with magnets on the support device, preferably on its underside, has proven advantageous for this purpose. These magnets are detected by stationary Hall sensors, and the magnetic arrangement has, for example, a spatial coding to uniquely identify specific angular positions. To detect the angular position of the support device, the signals from the Hall sensors are continuously evaluated by the control unit during the rotation of the support device, and the determined angular position is synchronized with the measurement result of the accelerometer. This allows the control unit to determine the direction in which the balancing mass must be shifted to reduce, rather than increase, the imbalance.

[0025] It has proven advantageous to transmit the adjustment energy mechanically to the rotating support device. According to a correspondingly preferred embodiment of the invention, the automatic drive for the adjustment device comprises a drive shaft extending coaxially within the central axis, which is fixed to the housing and thus does not rotate in the laboratory system. The support device is rotatably mounted to the drive shaft, so that the support device rotates around the drive shaft, which does not rotate in the laboratory system. The central axis is preferably designed as a hollow axis, and the drive shaft projects from the hollow axis at an upper and lower end.The upper end of the central drive shaft is mechanically coupled to the adjustment mechanism via a gearbox, allowing the counterweight to be displaced radially to the central axis when the support structure is rotated relative to the drive shaft and when the gearbox drives the adjustment mechanism. The term "radial to the central axis" does not preclude the presence of an axial component in addition to the radially perpendicular component of the adjustment; for example, an oblique adjustment of the counterweight to modify other components of the inertial tensor.

[0026] The gearbox with reversing direction of rotation defines three gearbox states, namely firstly an idle state, secondly a first drive state for moving the counterweight in a first direction and thirdly a second drive state for moving the counterweight in a second direction opposite to the first direction.

[0027] The automatic drive for the adjustment device preferably comprises a linear actuator in addition to the drive shaft. This actuator moves the drive shaft parallel to the central axis to reverse the direction of rotation of the gearbox. The drive shaft thus simultaneously acts as a control rod for switching the gearbox, representing a simple, space-saving, and reliable solution.

[0028] The linear actuator for the axial displacement of the drive shaft / control rod is preferably attached to the base plate of the housing and drives the axial displacement of the drive shaft / control rod at its lower end, which protrudes downwards from the hollow shaft. This arrangement is space-saving and easy to maintain.

[0029] According to a preferred embodiment of the invention, the transmission is a switchable bevel gear transmission with a pair of opposing bevel gears mounted axially on the drive shaft. Transversely to the drive shaft, the bevel gear pair engages in opposite directions with a third bevel gear, which drives the adjusting device. By means of linear displacement of the drive shaft, either the first bevel gear or the second bevel gear of the bevel gear pair is selectively engaged with the drive shaft in order to drive the third bevel gear, which engages with the first and second bevel gears on opposite sides, either counterclockwise or clockwise, depending on which of the first and second bevel gears is engaged with the drive shaft.

[0030] According to this, the three gear states of the bevel gear drive are: a) an idle state in which the bevel gear unit rotates freely with the carrier device around the drive shaft, so that no adjustment of the adjusting device takes place, b) a first drive state in which the drive shaft is engaged with the first bevel gear in order to drive the third bevel gear and thus the adjusting device in a first direction and c) a second drive state in which the drive shaft engages with the second bevel gear in order to drive the third bevel gear and thus the adjusting device in a second direction opposite to the first direction, while the carrier device rotates in the same direction.

[0031] This means that the automatic drive of the adjustment device, which can be controlled from outside the carrier device, is achieved indirectly by means of the mill's overall drive motor through a controllable force transmission between the drive shaft and the bevel gear drive.

[0032] Preferably, the adjusting device comprises a spindle drive for radially displacing the counterweight, e.g., consisting of a threaded spindle and a corresponding internal thread. The spindle drive can therefore be driven in either direction, independent of the direction of rotation of the support device, by means of the gearbox's direction switch. When the drive shaft is engaged with the gearbox, the drive, consisting of the drive shaft and gearbox, transmits the movement or force to the adjusting device, more precisely to the spindle drive, which radially displaces the counterweight. The threaded spindle preferably extends through an internal thread in the, for example, substantially U-shaped counterweight along its axis of symmetry.

[0033] The output from the bevel gear drive to the adjusting device is therefore achieved via the third bevel gear, which drives the spindle drive when the drive is in one of the two operating states. Advantageously, the third bevel gear directly drives the spindle of the spindle drive.

[0034] In the idle state, the self-locking mechanism of the adjusting device's spindle drive prevents internal rotation of the bevel gear drive, i.e., relative rotation between the bevel gears. However, to rotate the third bevel gear around its axis, which runs perpendicular to the central axis, and thus drive the adjusting device, only the self-locking mechanism of the spindle drive needs to be overcome.

[0035] Preferably, the drive shaft extends coaxially through the first and second bevel gears and has a drive lug between them. In the idle state, the bevel gear pair, and thus the bevel gear drive, rotates freely around the drive shaft. The drive shaft can then be brought into drive engagement with either the first or the second bevel gear by axial linear displacement, whereby the drive lug establishes a secure, preferably frictional and / or positive-locking connection with the respective first or second bevel gear. This fixes the corresponding first or second bevel gear rotationally relative to the housing, since the drive shaft is not rotatable with respect to the housing.Thus, the corresponding first or second bevel gear is set into rotation relative to the carrier device, which in turn sets the third bevel gear into rotation perpendicular to the central axis, thereby driving the adjusting mechanism. Due to the selectable positive connection with the first or second bevel gear, the third bevel gear, and thus the adjusting mechanism, can be driven in the desired direction regardless of the direction of rotation of the carrier device. The driver is designed, for example, as a thickening of the drive shaft to form a conical seat, a ball seat, a cylindrical face, or similar coupling mechanisms. However, a positive-locking engagement is also conceivable.

[0036] Preferably, the ball mill further comprises a switching state detector on the drive shaft, which detects the axial position of the drive shaft in order to detect at least one switching state, in particular the idle state of the gearbox.

[0037] Preferably, the support device comprises a rotating holding device for the balancing mass, on which the balancing mass is radially displaceable. The bevel gear drive is attached to the holding device in order to rotate with the support device.

[0038] According to an advantageous embodiment of the invention, the automatic drive of the adjusting device comprises a slip clutch which drives the spindle up to a predefined maximum torque and slips when the maximum torque is exceeded, e.g., when the counterweight runs against a stop (e.g., the outermost inner or outermost position) and the drive, e.g., due to a control error, continues to attempt to drive the adjusting device. This advantageously prevents damage to the gearbox or drive.

[0039] Accordingly, the invention provides a ball mill in which the imbalance is measured during the rotation of the carrier device and the counterweight is adjusted depending on the measured imbalance in order to automatically compensate the moment of inertia of the grinding station with the counter-moment of inertia and to ensure low-vibration operation in both directions regardless of the direction of rotation of the carrier device.

[0040] Preferably, the carrier device is accelerated to a target speed, and the imbalance is continuously measured during acceleration, particularly regularly or continuously, and transmitted to the control unit. Depending on the measured imbalance, the adjustment of the counterweight is controlled, thus forming a control loop for adjusting the counterweight. This control continues at least until the ball mill reaches the target speed, preferably even until the end of the grinding process. In other words, the moment of inertia is continuously controlled by means of the feedback signal from the measuring device to the control unit, at least during the start-up of the ball mill.The measured imbalance is therefore transmitted to the control unit and evaluated at least during the entire duration of the start-up process in order to continuously control the adjustment of the counterweight as the rotational speed increases, whereby the adjustment of the counter-inertia can take place stepwise or in several steps.

[0041] The invention will now be explained in more detail with reference to exemplary embodiments and the figures, wherein the features, regardless of whether they are disclosed in the description, the claims, the figures or otherwise, also individually define essential components of the invention, even if they are described together with other features. Brief description of the characters

[0042] They show: Fig. 1. A three-dimensional view of a planetary monoball mill with the housing open. Fig. 2 a cross-section through the support device with grinding station, leveling mass and housing base plate, Fig. 3 A three-dimensional view of the carrier device with the grinding station hidden, from a slanted top view, Fig. 4 a cross-section through Fig. 3, Fig. 5a a cross-section through the bevel gear unit in idle state, Fig. 5b a cross-section through the bevel gear in the first drive state, Fig. 5c a cross-section through the bevel gear in the second drive state, Fig. 6 an enlarged section from Fig. 2, Fig. 7 a schematic view of the inner end face of the threaded spindle, Fig. 8 an enlarged section from Fig. 4 in the area of ​​the linear actuator, Fig. 9 A view of the housing base plate from a low angle. Detailed description of the invention

[0043] Fig. Figure 1 shows a planetary monoball mill 1 according to the invention with a housing 2. The housing 2 has a lid 4 that can be opened to access the inner grinding chamber 6 of the planetary monoball mill 1, in which the carrier 8 rotates. In this example, the lid 4 is designed as a rotating lid, but a hinged lid can also be used, for example. A single grinding station 10 with one or more stacked grinding vessels 12 is rotatably mounted eccentrically on the carrier 8. A mass balancing device 14 for compensating the moment of inertia of the single grinding station 10 is arranged on the carrier 8 opposite the grinding station 10.

[0044] Referring to Fig. 2. The grinding station 10 has a receiving device 16 for receiving the grinding vessel 12, in which the grinding vessel 12 is firmly clamped to withstand the high dynamic forces that occur in a planetary ball mill. In the present embodiment, the grinding vessel has a capacity of 500 ml, which is already a relatively large grinding vessel for a laboratory planetary ball mill, and the support device rotates at a maximum speed of approximately 800 revolutions per minute. These are relatively demanding conditions for such a mill. However, the invention can also be used for laboratory planetary ball mills with smaller grinding vessels, e.g., 80 ml or 250 ml.

[0045] The support device 8 comprises two disc-shaped blocks 18 and 19, bolted together, in the form of a pulley 18 and a support disc 19. A drive motor, via a V-belt (both not shown) and the pulley 18, rotates the support device 8 around the central axis 20, causing the grinding station 10 with the support disc 19 to rotate in a circular path around the central axis 20. A toothed belt drive 22, coupled to the belt drive of the pulley 18, additionally drives the self-rotation of the grinding station 10 around the eccentrically mounted planetary axis 24, so that the grinding station rotates around the central or sun axis 20 and simultaneously rotates around its own planetary axis 24. In this embodiment of a planetary ball mill, these two directions of rotation are opposite.

[0046] The central axis 20 is rigidly attached to the housing base plate 32 and has a mounting flange 34 for this purpose, which is screwed to the housing base plate 32 by means of screws 36. The support device 8 is rotatably mounted on the stationary central axis 20, which is designed as a bearing journal, by means of two ball bearings 28, 30. The housing base plate 32 also has vibration-damping feet 38.

[0047] The coupled belt drive 22 comprises a first toothed belt pulley 26, which is mounted between the two ball bearings 28, 30 on the central axis 20, and a second toothed belt pulley 27, by means of which the self-rotation of the grinding station 10 about the planetary axis 24 is driven via the toothed belt 31. In the present planetary monoball mill, the speed ratio of the self-rotation of the grinding station 10 about the planetary axis 24 relative to the rotation about the central axis 20 (so-called relative speed ratio k) is k = -2. An integer relative speed ratio such as k = -2 has the advantage that the grinding station 10 is always positioned in the same orientation at the front discharge position under the rotating housing cover 4. If this is not necessary, other relative speed ratios, especially between k = -1.6 and k = -2.2, or between k = -1.7 and -2.0, may also be considered, possibly in conjunction with a different center distance.At speed ratios in these ranges, a particularly high energy input into the material being ground takes place, so that a high grinding performance can be achieved.

[0048] The central axis 20 is designed as a hollow axis, with a drive shaft 40 extending axially in the central channel 21 of the central axis 20. Both the central axis 20 and the drive shaft 40 are rotationally fixed in the laboratory system, and the support device rotates with the grinding station 10 on one side and the mass balancing device 14 on the other about the central axis 20 and the drive shaft 40.

[0049] Referring to the Fig. 2, Fig. 3 to Fig. The mass balancing device 14 comprises a rigid holding device 44 for the balancing mass 46, connected to the carrier disk 19 of the carrier device 8. In horizontal section, the balancing mass 46 essentially has a splayed U-shape with a central section 48 and two legs 50, 52 extending obliquely outwards. This shape of the balancing mass 46 saves space, as the legs 50, 52 can be extended beyond the central axis 20 to minimize the counter-inertia.

[0050] The compensating mass 46 is mounted in the holding device 44 so as to be linearly displaceable transversely to the central axis 20. Different grinding vessels 12 have different masses, e.g., due to different materials, wall thicknesses, or grinding vessel sizes, and thus different moments of inertia with respect to the central axis 20. In the example shown here, the grinding vessel 12 is a double-walled grinding vessel with a 500 ml grinding cup 54, consisting of a stainless steel housing 56 and an agate inlet 58. The grinding cup lid 60 also consists of a stainless steel housing 62 and an agate inlet 64. In addition to the grinding cup 54 itself, the grinding cup contents (not shown) of grinding balls and material to be ground also contribute to the variable moment of inertia of the grinding station 10. The moment of inertia of the grinding station 10 is balanced by the counter-moment of inertia of the holding device 44 and the radially displaceable compensating mass 46.The counter-moment of inertia of the mass balancing device 14 can therefore be changed to compensate for the changing moment of inertia of the grinding station 10 by displacing the balancing mass 46 radially with respect to the central axis 20. The linear radial drive, and thus the adjustment of the balancing mass 46, is effected by an adjustment device 65, which comprises a threaded spindle 66 and a threaded insert 68 in the balancing mass 46, in which the threaded spindle 66 is guided.

[0051] Referring to the Fig. In sections 5a to 5c, the radially extending threaded spindle 66 to the central axis 20 and drive shaft 40 is driven by a switchable planetary gear set, in this example designed as a bevel gear set, which is attached to the holding device 44. For this purpose, the gear set 70, designed as a bevel gear set, has a U-shaped bracket 72, which is attached to a vertical support 45 of the holding device 44 by screws 74.

[0052] In the holder 72, an upper and lower bevel gear 76, 78 are rotatably mounted by means of ball bearings 80, 82. The two bevel gears 76, 78 each have a coaxial central bore 84, 86 through which the vertical drive shaft 40 extends. The upper and lower bevel gears 76, 78 are positioned opposite each other at their ends and engage on opposite sides with the third bevel gear 88, which is mounted on the horizontal drive shaft 90 of the threaded spindle 66 and directly drives it. The drive shaft 40 is rotatably and linearly displaceably mounted in the gearbox 70 by means of bearings 81, 83.

[0053] The drive shaft 40 has a driver 92 in the form of a thickening between the upper and lower bevel gear 76, 78. Fig. Figure 5a shows the idle state of the bevel gear transmission 70, in which both the upper and lower bevel gears 76, 78 are not engaged with the drive shaft 40, but rotate freely around the drive shaft 40, since the driver 92 is in a neutral position and is not in engagement with either of the two bevel gears 76, 78. Therefore, the gears in the Fig. In the idle state shown in Figure 5a, the entire bevel gear drive 70 rotates freely around the drive shaft 40, so that the horizontal drive shaft 90 and the threaded spindle 66 are not driven. In this idle state, the self-locking mechanism of the spindle drive 66, 68 prevents radial movement of the counterweight 46, so that the moment of inertia does not change.

[0054] To adjust the counterweight 46 during the rotation of the carrier device 8, the drive shaft 40 is either moved upwards ( Fig. 5b) or downwards ( Fig. 5c) is shifted until the driver 92 is in close engagement with either the upper bevel gear 76 or the lower bevel gear 78. Then, with the same direction of rotation of the carrier device 8, either the upper bevel gear 76 is stationary relative to the device housing 2, thus driving the horizontal drive shaft 90 in one direction, or the lower bevel gear 78 is stationary relative to the device housing 2, thus driving the horizontal drive shaft 90 in the other direction, since the gearbox 70 rotates around the drive shaft 40 and a constraint is created between the respective stationary bevel gear 76 or 78 on the one hand and the third bevel gear 88 on the other. Thus, without reversing the direction of rotation of the carrier device 8, the spindle drive 66, 68 can selectively move the counterweight 46 either towards a higher moment of inertia (outwards) or towards a lower moment of inertia (inwards).The drive shaft 40 thus also functions as a push rod for controlling the gearbox 70.

[0055] In this embodiment, the engagement of the drive shaft 40, or the driver 92 within the hollow bore 84 or 86, with the upper or lower bevel gear 76, 78 is achieved by means of a frictional connection via a conical seat between the driver 92 and the respective bevel gear 76 or 78. For this purpose, the driver 92 or the thickening has conical end sections 92a, 92b and the two bevel gears 76, 78 have matching conical bores 84, 86.

[0056] Referring to the Fig. 6 and Fig. The threaded spindle 66 comprises the horizontal or centrally extending radial drive shaft 90 and a coaxial threaded sleeve 94, wherein the horizontal drive shaft 90 is rotatably mounted on both sides in the holding device 44. The threaded sleeve 94, and thus the counterweight 46, is driven by the horizontal drive shaft 90 via a detent and slip clutch 96. The detent and slip clutch 96 includes a spring-loaded ball plunger 98, which extends in a transverse bore 100 of the horizontal drive shaft 90 and engages radially in longitudinal grooves 102 in the threaded sleeve 94 in a positive-locking manner. With this internal positive-locking detent and slip clutch 96, the threaded spindle 66 is driven up to a predefined maximum torque via the detent connection 98, 102.Thus, the outer threaded sleeve 94 is driven by the spring-loaded plunger 98 to drive the threaded spindle 66, provided that the maximum driving torque of the spring-loaded plunger 98 in the longitudinal grooves 102 is not exceeded. However, if the maximum driving torque of the ball plunger 98 in the longitudinal grooves 102, or maximum torque for short, is exceeded, e.g., if the counterweight runs against the inner or outer stop 104, 106, the detent and slip clutch 96 slips to protect the mechanism from damage.

[0057] Referring to the Fig. 8 and Fig. 9 The drive shaft 40 is axially driven by a linear actuator 108, which is mounted in an opening 110 in the base plate 32. For this embodiment, a linear actuator of type L4218M1404 from Nanotec is used (see www.nanotec.de). The linear actuator 108 is attached to the base plate 32 from below by a flange plate 116. At its lower end 112, the drive shaft 40 includes an axle or shaft section 114, which belongs to the linear actuator 108 and is directly driven linearly by the linear actuator 108 to move the entire drive shaft 40 axially.

[0058] The axle or shaft section 114 of the linear actuator 108, and thus the drive shaft 40, protrudes from the underside of the linear actuator 108. At this lower end 112, the drive shaft 40 is coupled to a displacement detection device 118, which detects the axial position of the drive shaft 40. In this example, an aperture 120 is attached to the lower end of the drive shaft 40, which moves axially with the drive shaft 40, and whose axial position is detected by a photoelectric sensor 122. The photoelectric sensor is attached to the flange plate 116 by a circuit board 126. The drive shaft 40, including the axle or shaft section 114 of the linear actuator 108, therefore protrudes downwards from the base plate 32 to detect the axial position of the drive shaft 40.

[0059] In the illustrated example, the position detection device 118 detects the neutral position of the push rod or the drive shaft 40, i.e., the idle state of the gearbox 70, and is thus an example of a switching state detector for the gearbox 70. For the upper or lower drive state of the gearbox 70, the push rod or the drive shaft 40 is pushed further upwards or downwards by the linear actuator into the respective bevel gear 76, 78, thereby engaging the thickened section of the drive shaft 40 in the respective bevel gear 76, 78, thus locking it in place and indirectly driving it. When the drive shaft 40 is pushed to its end position in the respective bevel gear 76, 78, the current consumption of the linear actuator 108 increases. A current measuring device detects this increase in current and thus the upper or lower end position of the drive shaft 40, i.e., the first or second drive state.However, it is also conceivable to detect all three states with the same measuring device, e.g. via a light barrier arrangement or a rotary encoder on the threaded spindle 66 as a switching state detector.

[0060] Referring again to Fig.A two-dimensional accelerometer 128 is attached to the device housing 2, specifically to the base plate 32. If the support device 8 rotates and the counterweight 46 is not optimally adjusted, the support device 8 vibrates and transmits this vibration to the suspension with the base plate 32. The accelerometer 128 measures the direction and magnitude in both dimensions (x and y directions) of the horizontal plane of the acceleration of the base plate 32 generated by the unbalance vibrations. The measured acceleration vector rotates perpendicular to the central axis 20 and thus spans an acceleration ellipse, the magnitude of which represents a measure of the unbalance. Due to differing stiffness in the two dimensions of the horizontal plane, the acceleration ellipse can be significantly eccentric.Therefore, for the quality of the control signal, it is advantageous to determine the magnitude of the acceleration along the first principal axis of the ellipse and to use this as a measurement variable for the control device 130, by means of which the automatic adjustment of the counterweight 46 is controlled.

[0061] It is evident to the person skilled in the art that the embodiments described above are to be understood as examples, and that the invention is not limited to these, but can be varied in many ways without leaving the scope of protection of the patent claims.

Claims

[1] Ball mill (1), in particular planetary or centrifugal ball mill on laboratory scale, comprising a housing (2), a support device (8) which is rotatably mounted relative to the housing (2) about a central axis (20), at least one grinding station (10) with a receiving device (16) for at least one grinding vessel, which is rotatably mounted about a planetary axis (24) to the support device (8) and is carried by the latter about the central axis (20) and at least one grinding vessel (12) which can be filled with material to be ground and grinding balls and inserted into the receiving device (16), a drive (18) for the carrier device (8), a drive (22) for the receiving device (16), a mass balancing device (14) with an adjustable balancing mass (46) to form a counter-moment of inertia for the grinding station or grinding stations (10), an adjusting device (65) for adjusting the counterweight (46) in order to change the counter-moment of inertia adapted to the moment of inertia of the grinding station or grinding stations (10), an automatic drive for the adjustment device (65), characterized by , that the counterweight (46) is adjustable in different directions independently of the direction of rotation of the support device (8) in that the automatic drive for the adjustment device (65) has a switchable gearbox (70) with reversal of direction of rotation, wherein the switchable gearbox (70) defines an idle state, a first drive state for moving the counterweight in a first direction and a second drive state for moving the counterweight in a second direction opposite to the first direction. [2] Ball mill (1) according to claim 1, designed as a mono-ball mill with only one grinding station (10), wherein the mass balancing device (14) with the adjustable balancing mass (46) is arranged opposite the one grinding station (10) with respect to the central axis (20) in order to form a counter-moment of inertia for the one grinding station (10). [3] Ball mill (1) according to claim 1 or 2, comprising a measuring device (128) for measuring the imbalance, and a control device (130) which controls the automatic drive of the adjustment device (65) depending on the measured imbalance in order to automatically adapt the counter moment of inertia to the moment of inertia of the grinding station or grinding stations (10) by means of displacement of the balancing mass (46), wherein the displacement of the balancing mass (46) is automatically controlled in the direction in which the imbalance is reduced without reversing the direction of rotation of the support device (8). [4] Ball mill (1) according to one of the preceding claims, wherein the energy used for the automatic adjustment of the counterweight (46) is taken from the rotational energy of the carrier device (8), in that the automatic drive of the adjustment device (65), without a separate motor of its own, is mechanically powered from the rotation of the carrier device (8) relative to the housing (2). [5] Ball mill (1) according to one of the preceding claims, wherein the automatic drive for the adjusting device (65) comprises a drive shaft (40), wherein the support device (8) is rotatably mounted relative to the drive shaft (40) and wherein the drive shaft (40) is coupled to the adjusting device (65) by means of a transmission (70) such that the counterweight (46) is radially displaceable when the support device (8) is rotated relative to the drive shaft (40). [6] Ball mill (1) according to one of the preceding claims, wherein the automatic drive for the adjusting device (65) comprises a drive shaft (40) and a linear actuator (108) which displaces the drive shaft (40) parallel to the central axis (20) in order to switch the direction of rotation of the gearbox (70). [7] Ball mill (1) according to one of the preceding claims, wherein the central axis (20) is designed as a hollow axis and the automatic drive for the adjusting device (65) comprises a drive shaft (40) which runs coaxially inside the hollow axis (20) and is mounted in a rotationally fixed manner relative to the housing (2), so that the support device (8) rotates coaxially around the drive shaft (40) which is fixed in the laboratory system when the ball mill (1) is operated. [8] Ball mill (1) according to claim 7, wherein the automatic drive has a switchable bevel gear transmission, wherein the drive shaft (40) is linearly displaceable at least between three positions in order to switch at least the following three switching states of the transmission (70): a) an idle state in which the bevel gear unit with the carrier device (8) rotates freely around the drive shaft (40), so that no adjustment of the adjusting device (65) takes place, b) a first drive state in which the drive shaft (40) engages with a first bevel gear (76) to effect a drive of the adjusting device (65) in a first direction and c) a second drive state in which the drive shaft (40) engages with a second bevel gear (78) to effect a drive of the adjusting device (65) in a second direction opposite to the first direction, while the carrier device (8) rotates in the same direction. [9] Ball mill (1) according to claim 8, wherein the first and second bevel gears (76, 78) are engaged opposite each other at their ends with a third bevel gear (88) and the third bevel gear (88) is in drive connection with the adjusting device (65), wherein the drive shaft (40) has a driver (92) which, when the drive shaft (40) is moved, can be selectively brought into close contact with the first or second bevel gear (76, 78) in order to fix the respective first or second bevel gear (76, 78) rotationally relative to the housing (2) and thus to set it in rotation relative to the support device (8) in order to drive the adjusting device (65) in the desired direction regardless of the direction of rotation of the support device (8). [10] Ball mill (1) according to one of the preceding claims, further comprising a switching state detector (118) which detects at least one switching state of the transmission (70). [11] Ball mill (1) according to one of the preceding claims, wherein the support device (8) comprises a co-rotating holding device (44) for the counterweight (46) on which the counterweight (46) is suspended radially displaceable and wherein the gearbox (70) is attached to the holding device (44). [12] Ball mill (1) according to one of the preceding claims, wherein the drive of the adjusting device (65) comprises a slip clutch (96-102) which slips when the counterweight (46) runs against a stop (104, 106) and the drive continues to attempt to drive the adjusting device (65). [13] Ball mill (1) according to one of the preceding claims, wherein the adjusting device (65) comprises a spindle drive (66, 68) for radial displacement of the counterweight (46) and the spindle drive (66, 68) can be driven selectively in both directions by means of direction switching of the gearbox (70) independently of the direction of rotation of the carrier device (8).

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