Machine for fractionating ground grain products

Abstract

The machine for fractioning ground grain products is a plansifter or a cleaning machine for example, having a plurality of sieve stack pairs arranged next to each other, each of which comprises an upper sieve stack (3) and a lower sieve stack (4). Each of the sieve stack pairs is paired with a drive module (20) which has an electric motor and a centrifugal weight that can be rotated by said electric motor. The drive module (20) is arranged between the upper and lower sieve stack of the respective sieve stack pair. The upper sieve stack (3) and the lower sieve stack (4) can be approximately the same size, i.e. the number of sieves of the upper sieve stack and of the lower sieve stack can be the same or can differ by maximally 50% or maximally 30% for example.

Description

[0001] MACHINE FOR FRACTIONING

[0002] GRAIN MILLING PRODUCTS

[0003] The invention relates to a machine for fractionating grain mill products, for example a plansifter or a cleaning machine.

[0004] Machines for fractionating grain mill products are used to separate

[0005] Components of a ground material into coarser and finer grained components and, depending on the case, components of different densities and / or the removal of

[0006] Foreign bodies from the ground material. The separation of the ground material into different granular components is also called «classifying» or «fractionating». Plan sifters are generally used in grain mills to fractionate the ground grain products between and after passes through the roller mill of a grain mill. Also for a so-called control sifting, ie the

[0007] They can be used to sift through flour that is otherwise ready for sale.

[0008] Plan sifters feature stacks of sieves acting as plan sieves, often enclosed in so-called 'sieve compartments' or 'sieve boxes' with side walls and a lid. These sieves are set into horizontally oscillating movements by a drive mechanism, particularly circular oscillations in the sieve plane. According to the state of the art, the drive works as follows: An even number of sieve boxes are coupled together and arranged in two rows. Between the rows is a drive module containing a flywheel, which is set in a circular motion via a belt drive. The sieve box group with the drive module is suspended so that the flywheel on the one hand and the center of gravity of the sieve boxes on the other hand together form a flywheel system and orbit around a common axis of rotation (orbital axis) offset by 180° to each other.

[0009] This proven system has the first disadvantage that a gap must be maintained between the rows of screen boxes to accommodate the drive module, which requires a corresponding amount of space. Second, there is the disadvantage of limited adaptability: in order to increase or decrease the number of screen boxes, a drive dimensioned for the maximum number of screen boxes must always be used, meaning the drive is oversized for many applications. Third, the forces acting on the bearings of such a flywheel are considerable, and the requirements are correspondingly high.

[0010] Standalone plansifters consisting of a single screening compartment with a drive are also known. FR 1 426 099 and FR 840 946 each show an embodiment of such a standalone plansifter with a drive module arranged in the center, i.e., between an upper and a lower partial screen stack. GB201013 shows plansifters with one or two screening compartments, with a drive module in the center. In designs with two screening compartments, a common drive module is provided for both screening compartments.

[0011] EP 2 114 582 proposes providing each screening compartment with its own drive so that the plansifter can have not only an even but also an odd number of screening compartments. The drive comprises a drive device on the lid and one on the base, wherein the drive devices consist of annular toothed disks that interact with coils arranged on the outer ring and together with these form a reluctance motor. Inlet openings and outlet openings are arranged inside the toothed disks. This solution enables a flexible arrangement of the screening compartments. However, the performance of the drive units is limited, and the need for one drive unit each on the lid and the base makes the design comparatively complex.

[0012] It is an object of the invention to provide a machine for fractionating grain mill products, in particular a plansifter or a cleaning machine, which overcomes disadvantages of the prior art and which is flexible, robust and simple in construction.

[0013] According to one aspect of the invention, the machine for fractionating ground grain products comprises a plurality of sieve stack pairs arranged side by side, each having an upper sieve stack and a lower sieve stack. Each sieve stack pair is assigned a drive module which has an electric motor and a flywheel weight driven by the latter to rotate, i.e., a mass arranged eccentrically with respect to the axis of rotation of the rotation. The drive module is arranged between the upper and lower sieve stacks of the respective sieve stack pair. The upper sieve stack and the lower sieve stack can be approximately the same size, i.e., the number of sieves in the upper sieve stack and the lower sieve stack can be the same or differ, for example, by a maximum of 50% or a maximum of 30%. The machine is, for example, a plansifter or a cleaning machine for separating impurities from the ground product.

[0014] The pairs of sieve stacks arranged next to each other are mechanically coupled to each other in the sense that they can perform common, particularly horizontal, circular oscillations.

[0015] In this text, "screen stack" refers to an arrangement of screens arranged one above the other. The screens do not necessarily have to rest on top of each other, but can also be held by an external support structure, such as a box with slots for the screens.

[0016] Through the rotating movements of the flywheels, the machine is designed to cause the sieve elements of the sieve stacks to vibrate, for example, in the form of circular movements. In the context of this text, circular movements are included when referring to "vibrations."

[0017] The arrangement with a drive module between the upper and lower screen stacks has the advantage that the flywheel weight is distributed discretely to the point where the inertial forces occur per screen stack pair. This discretely divides and minimizes force flows. The required bearings are therefore subjected to less stress and can be smaller, and / or their service life can be increased. The overall mass is also reduced, which in turn has a positive effect on the bearings. Furthermore, no additional space is required for a central drive unit between the screen stacks. Furthermore, the inventive approach also allows the machine to be constructed from virtually any number of screen stack pairs, with the drive always being suitably dimensioned by design, and energy consumption and material wear being adapted to the number of screen stack pairs.

[0018] The sieve stacks can be arranged in sieve boxes, as is conventional. Alternatively, the use of such closed boxes can be dispensed with by designing the sieve elements so that they can be stacked on top of each other without the need for an external housing structure.

[0019] The sieves of the sieve stacks are primarily flat sieves, meaning they are horizontally aligned. The sieve plane is therefore parallel to the vibration plane.

[0020] The machine is specifically designed so that the flywheel weights of the drive modules oscillate synchronously.

[0021] The drive modules can each have a shaft that rotates relative to a base body, such as a housing, to which the flywheel is attached. The shaft can be mounted relative to the base body in a conventional manner using a bearing, such as a ball bearing, at each end of the shaft. The dimensions of the bearings are adapted to the constant load exerted on them during operation by the rotating flywheel, which is significantly lower than that of corresponding bearings in state-of-the-art central drive modules.

[0022] In some embodiments, the shaft is driven directly by the electric motor, with the electric motor's rotor connected to it in a rotationally fixed manner, or even by a magnetic section of the shaft, for example. Such a solution, which is free of gears or other speed-dependent elements (such as belts or similar), is particularly compact and also requires very little maintenance.

[0023] The motors can be synchronous motors, especially those with permanent magnets. Both internal rotor and external rotor motors are conceivable, although an arrangement with an internal rotor featuring permanent magnets can be particularly efficient.

[0024] The drive modules can each have a plurality of passage channels for the material to be screened. This allows the intended portions of the material to be transferred from the upper screen stack to the lower screen stack and then to the designated location. Thanks to the passage channels, this is possible without the need for a separate device on the outside of the screen compartments and / or drive modules for passing these portions through. This contributes to the compact design.

[0025] By providing the passage channels, the sieve stack pairs form functional units which functionally correspond to a sieve stack / sieve compartment of a plansifter (or a cleaning machine) according to the state of the art, which has approximately the same number of sieves as the upper and lower sieve stacks together.

[0026] The passage channels can, in particular, be located radially outside the path of the flywheel. This enables a design in which the flywheel is firmly attached to the shaft of the drive module. The passage channels can be designed as elongated slots. With a rectangular drive module layout, they can run parallel to the radially outer sides. The number of passage channels can be, for example, eight. A rectangular, for example, square, layout of the drive modules can be particularly advantageous because it allows the drive modules to be arranged side by side, for example, in a simply constructed frame.

[0027] Such a common frame can be advantageous regardless of the shape of the drive modules. It can form the mechanical support structure of the machine and also include structures for a suspension device by which the machine (here, this refers to the parts of the machine that are to be set in circular vibration, i.e., of course, excluding control and power electronics components) can be suspended. Furthermore, the frame can accommodate the upper screen stacks by having them rest directly or indirectly (e.g., via the drive modules on which they rest) on the frame, while the lower screen stacks are suspended from them.

[0028] Such a common frame accommodates the drive modules together. The drive modules thus share a common mechanical support structure and are mechanically coupled to one another. The machine is therefore not simply an ensemble of several standalone sifters arranged side by side, but a larger mechanical unit. It turns out that the concept of "one centrally arranged drive module per pair of screen stacks" with the shared mechanical support structure allows the advantages of standalone plansifters (flexibility) to be combined with the advantages of larger machines (particularly higher efficiency), while consistently optimizing drive power and requiring minimal space.

[0029] Such a common frame will, in particular, be positioned centrally in relation to the vertical axis, i.e., between the upper and lower screen stacks. The drive modules—that is, their electric motors and flywheels with housing—are housed in the common frame. In particular, they can be housed directly in the frame, i.e., they do not rest on a screen of the screen stack.

[0030] Additionally or alternatively, the frame can also accommodate electrical cables to supply the electric motors, e.g. inside the frame parts that form the frame.

[0031] In some embodiments, a majority of the electric motors of the drive modules are connected to a common power stage, meaning they are powered by the common power stage. This allows for savings in power electronic components, cables, etc. Even if one drive module, and thus one electric motor, is present per screen stack pair, thus requiring more electric motors than in the prior art, the electric motors per cluster with a common power stage can be operated and supplied as a single electric motor, which is very economical.

[0032] If the machine contains several such electric motor clusters and accordingly several power levels, the control for the circuit breakers in the power levels can be carried out by a common control module.

[0033] Alternatively, each drive module can have its own power level.

[0034] In some embodiments, the machine is configured so that the speed of the electric motors is selectable and can be read off. The screening efficiency can be optimized, for example, depending on the material to be screened—particularly by selecting the appropriate speed. Particularly in embodiments with at least one electric motor cluster with a common power stage, the drive modules can also be equipped with a mechanical stop that limits movement against the intended direction of rotation (reverse rotation) of the flywheel weights, while movement in the forward direction (the intended direction of rotation) is not impeded.

[0035] The machine can then be configured to perform the following procedure upon start-up: First, the flywheel weights are slowly moved in reverse until they rest securely against the mechanical stop. The motors are thus initially moved very slowly and with very little current backward until they reach a mechanical stop. If a motor reaches a mechanical stop, the electrical rotating field continues to rotate; the stall torque is exceeded. The rotating field continues to rotate so that the other motors can continue to rotate toward the stop. This reversing process continues until all motors are at their mechanical stop. This can be ensured by subjecting the rotating field to a rotation of approximately 360° or more.

[0036] This procedure may, where appropriate, be carried out for each performance level.

[0037] The mechanical stop can in particular be formed by a pendulum element which can be deflected relative to the flywheel between a home position and a deflected position. When the pendulum element is in the home position, it will rest against a stop element during a backward movement when the flywheel has reached an angular position defined by the stop element. During a forward movement, the pendulum element is deflected by a ramp so that the stop element does not impede movement in the forward direction. Furthermore, the pendulum element can be designed such that, due to its center of gravity, it is deflected into the deflected position by centrifugal force when the flywheel rotates fast enough so that it does not come into contact with the ramp during each revolution.

[0038] As an alternative to the procedure described above, alternative methods for aligning the flywheels are also possible. For example, instead of using a mechanical stop, the motors within a cluster could be individually controlled with switches ("contactors"). This would involve moving the motors one after the other to a specific position using an encoder or resolver. Under certain circumstances, a means could then be provided, such as a friction brake, to hold the motors in position before they are all set into synchronous rotation by supplying them with the appropriate power.

[0039] Optionally, for example, there can be a sensor per drive module that detects the position of the flywheel, e.g. by determining when the flywheel is in the immediate vicinity of a sensor position.

[0040] In embodiments where each drive module has its own power stage, such a sensor signal may be sufficient for alignment. Synchronization of the rotary movement can then also occur during ongoing—or especially during initial—operation.

[0041] In addition to the machine, a method for operating the machine is also the subject of the present invention. The method comprises, in addition to providing the machine as defined above, with or without special features of embodiments of the invention, the step of synchronously driving the flywheels of the drive modules to cause the screening compartments to vibrate. For this purpose, the machine—or more precisely, a mechanically coupled unit consisting of the screening stacks and the drive modules and, if applicable, the frame; excluding the machine's control and power electronics components—is mounted, e.g., suspended, in such a way that it is capable of horizontal circular vibrations.

[0042] Optionally, the process also includes the step of starting the machine, whereby the flywheel weights are first moved slowly backwards until they reach a mechanical stop and only then are they driven by their electric motors to rotate in the forward direction.

[0043] Embodiments of the invention are described below with reference to the drawings. In the drawings, like reference numerals denote like or similar elements. The drawings show partially corresponding elements in different sizes from figure to figure. They show:

[0044] Fig. 1 : a view of a plansifter;

[0045] Fig. 2: The view of the plansifter according to Fig. 1 with partially removed sieve stacks and with two removed drive modules;

[0046] Fig. 3 a bottom view of the frame;

[0047] Fig. 4 is a view of a drive module for a plansifter according to Fig. 1;

[0048] Fig. 5 is a plan view of the drive module of Fig. 4;

[0049] Fig. 6 is a view of the drive module of Fig. 4 and Fig. 5, sectioned along the plane VI-VI; Figs. 7 and 8 are a detail of the drive module with two different positions of the pendulum bracket;

[0050] Fig. 9 is a diagram of the electric motors of the eight drive modules of the plansifter according to Fig. 1; and

[0051] Fig. 10 shows a plurality of possible arrangements of sieve stack pairs.

[0052] Figure 1 shows a plansifter 1 as used in grain mills. Figure 2 shows the plansifter with some of the screen stacks and some of the drive modules removed. The plansifter comprises a plurality of upper screen stacks 3 and lower screen stacks 4, shown only schematically, which are mounted on a common suspension device so that common horizontal oscillating movements are possible. In addition, the plansifter has flexible feed lines as the screening material inlet and also flexible outlet lines as the screening material outlet. Fig. 1 shows top-side inlets 6, to which the feed lines are connected, and bottom-side outlets 7 for the outlet lines. As an alternative to a design without an additional external screening unit housing, the screen stacks 3, 4 can also optionally be present in a separate screen box each.

[0053] A frame 11 serves as the mechanical support structure. It forms a supporting frame and accommodates the drive modules described in more detail below. The screen stacks are attached to the drive modules and thus indirectly to the frame 11, for example, by means of a clamping system consisting of rods and / or belts and / or other means; the clamping system is not shown in Figs. 1 and 2.

[0054] The frame 11 can have fastening structures 12 for the suspension device (which, for example, is formed in a conventional manner by flexible rods). Furthermore, it can form a cable guide for the drive modules 20, i.e., the frame 11 can also accommodate the electrical cables, for example, in a cavity inside the elements forming the support frame.

[0055] As can be seen particularly in the bottom view of the frame 11 according to Figure 3, the frame is essentially open. It has supports 13 on which the drive modules 20 are placed and relative to which they can also be secured. The supports 13 are arranged such that the drive modules 20 rest on them in the area of ​​their lower corners.

[0056] In Fig. 3 one can also see a possibility of an electrical supply 18, which connects the electric motor of the drive module 20 with the supply lines in the frame 11 and which is guided here along the underside of the drive module.

[0057] Figure 4 shows a drive module 20 in an oblique view from above. The drive module, defined by a housing 22, has a rectangular, in particular essentially square, footprint. Important for its function is the flywheel 23, which here is constructed from a plurality of plate elements 24 (other designs, e.g., from a monolithic block or other components, would also be possible) and which can be set in a circular motion by an electric motor described in more detail below. The direction of rotation 28 is represented in Fig. 4 by a block arrow; the axis of rotation 29 is also indicated in Fig. 4. In this text, terms such as "radial," "axial," etc., refer to this axis of rotation 29, unless expressly indicated otherwise.Of course, the functionality of this invention doesn't depend on the direction of rotation: The direction of rotation and everything associated with it could also be reversed, in which case the mechanical stop described in more detail below would be installed on the other side. The direction of rotation can, for example, be configurable.

[0058] The drive module 20 also has eight passage channels 25, one outer and one inner passage channel 25 along each side. All passage channels 25, including the inner passage channels, are arranged radially outside the path described by the flywheel 23. The flywheel 23 is constructed in such a way that it has a large mass and is arranged as far out as possible within the space available to it, which is why it has the approximate shape of a ring segment whose axial (vertical) extent essentially corresponds to the entire vertical extent of the drive module.

[0059] In Fig. 4 one can also see a pendulum bracket 41 and a stop plate 42 which serve to bring the flywheel weight 23 into a defined position before starting, which will be explained in more detail below with reference to Fig. 7 and Fig. 8.

[0060] Figure 5 shows the drive module in a top view, and Figure 6 shows a section through plane VI-VI in Figure 5. In addition to the passage channels 25, Figure 6 particularly shows the shaft 31, which is rotatably mounted relative to the housing 22 by a bracket 33, each with a ball bearing 32 on the top and bottom sides. The flywheel 24 is attached to the shaft 31 (attachment means 34).

[0061] Shaft 31 is directly connected to or forms the rotor of the electric motor, i.e., without gears, belts, gears, or other transmission means that could potentially convert the speed. In the illustrated embodiment, permanent magnets 35, mounted externally on shaft 31, form the rotor of the electric motor, while stator 36, with its coils and soft magnets for generating a rotating magnetic field, is attached to the housing.

[0062] Figures 7 and 8 illustrate one possibility for moving the flywheel to a defined position before starting the machine. This may be necessary if, for example, the flywheels of the various drive modules run out to different distances during a shutdown. If the flywheels 23 of the drive modules 20 are moved to a defined position in a common process before starting, synchronous operation is possible, even when multiple motors are operated with a common power stage (with a common power electronic converter).

[0063] For this purpose, a pendulum bracket 41 is attached to the flywheel 23, which cooperates with a stop plate 42 during a slow backward rotation (in Fig. 7 and 8 corresponding to a movement towards the observer) to form a stop, while a rotation in the opposite forward direction (direction of rotation 28 in Fig. 4) is not hindered.

[0064] The pendulum bracket is pivotally mounted about an axis 43. Fig. 7 shows the state in which the tip 44 of the pendulum bracket rests against the stop 45 formed by the stop plate 42 (which can, for example, be attached to a cover not visible in Figs. 7 and 8). A backward movement beyond the position shown in Fig. 7 is not possible.

[0065] A forward movement, however, is not prevented by the stop plate 42, since the radially inner narrow side of the stop plate 42 forms a ramp 48 which deflects the pendulum plate 41 during a forward movement. To ensure that the tip 44 of the pendulum plate 41 does not touch the ramp 48 with every revolution during a rapid rotation in the forward direction and the pendulum plate is not deflected, the center of gravity of the pendulum plate 41 is arranged below the axis 43. In the example shown, this is achieved by a weight section 47 of the pendulum plate 41 below the axis 43. When the flywheel is at rest or moving only slowly, the pendulum plate 41 is aligned vertically as shown in Fig. 7. During a rapid rotation, the centrifugal force causes a deflection into the position shown in Fig. 8, in which the tip 44 of the pendulum plate is radially inside the stop plate 42 and never touches it.

[0066] The machine can now be programmed so that upon start-up, it first slowly rotates the motors backward by at least approximately one full rotation, ensuring that all flywheel weights are safely pushed to their stops. They are then all in the defined position. The motors are then synchronized to rotate forward.

[0067] Figure 9 illustrates the principle of feeding several of the motors 51 of the various drive modules through a common power stage 53. Figure 9 illustrates eight motors, each motor belonging to one of the drive modules 20 and being a synchronous motor, for example, as described with reference to Figure 6, with a rotor having at least one permanent magnet 35. In the embodiment of Figure 9, four motors are assigned to each of the two power stages 53, thus forming a common motor cluster—in terms of control technology, they essentially correspond to a single motor. During operation, the motors with a common power stage 53 run synchronously per se, in that the same rotating field is generated in each of the motors, and the rotors follow the rotating field. The power switches in the power stages 53 are controlled by a common control module 52. For the absolute position, this module includes a position sensor for each power stage 53.

[0068] In the physical realisation of the machine and as an alternative to the configuration shown, the control system can also be an integral part of the power levels 53.

[0069] In some embodiments, the machine is configured so that the speed can be precisely specified and displayed using the control module 52. Screening efficiency can be optimized by selecting the appropriate speed.

[0070] Fig. 9 schematically shows an input and / or output unit 55, which can be used to set and read the speed. In Fig. 9, the input and / or output unit 55 is schematically illustrated as a computer that communicates with the control module via an interface. However, other solutions are conceivable, e.g., a control panel on the control module, a control element (slider, rotary knob, etc.) with a readout option, etc.

[0071] An advantage of the inventive approach already mentioned above is that the number and arrangement of the screen stack pairs is fundamentally freely configurable; even an odd number of screen stack pairs is possible. Figure 10 illustrates a variety of possibilities. Each of the images AI schematically represents an arrangement of screen stack pairs 3, 4 and also illustrates possible positions of fastening structures 12 for a suspension device. According to arrangement A, a machine can have only a single screen stack pair. Arrangements BD show 2, 3, or 4 screen stack pairs arranged in a row; longer rows are also conceivable. Arrangements EH each contain two rows of screen stack pairs.It can also be seen that, in contrast to the prior art, essentially no spacing is required between adjacent rows, whereas in the prior art the drive module is generally located between two rows, which is why they must be spaced apart, as is the case, for example, in arrangement I. Arrangements with two (or more) rows and with larger spacing between the rows, as shown in Figure 1 and with fewer or more pairs of screen stacks per row than shown in Fig. 10, are also an option for machines according to the present invention. The space between the rows can then be used appropriately if necessary, since it does not require a larger drive module spaced horizontally from the pairs of screen stacks, as is the case with screen stacks in the prior art.

[0072] Many other arrangements are conceivable. For example, in a rack as shown in Fig. 3, individual positions can remain unoccupied. Alternatively, arrangements with three rows of pairs of screen stacks or even irregular arrangements are also conceivable if the suspension is adapted accordingly.

Claims

PATENT CLAIMS 1. Machine for fractionating grain milling products, comprising a plurality of adjacent pairs of sieve stacks, each with an upper sieve stack (3) and a lower sieve stack (4), further comprising a drive module (20) between the upper and lower sieve stacks (3; 4) of a plurality of the sieve stack pairs, wherein the drive modules (20) each comprise an electric motor and a flywheel (23) which can be driven by the electric motor to a rotary motion.

2. Machine according to claim 1, which is configured to drive the flywheels (23) of the drive modules (20) synchronously.

3. Machine according to claim 1 or 2, wherein the drive modules (20) each have a shaft (31) rotatable relative to a base body, wherein the electric motors each have a stator (36) and a rotor (35) and wherein the rotor (35) is connected to the shaft (31) in a rotationally fixed manner or is formed by it.

4. Machine according to one of the preceding claims, wherein the electric motors are permanent magnet synchronous motors.

5. Machine according to one of the preceding claims, wherein the drive modules (20) each have a plurality of passage channels (25) through which portions of the grain milling product can pass from the upper sieve stack (3) to the lower sieve stack (4). Machine according to one of the preceding claims, wherein the drive modules (20) each have a housing (22) with a rectangular, in particular square, floor plan. Machine according to one of the preceding claims, comprising a frame (11) in which the drive modules (20) are accommodated. Machine according to claim 7, wherein the frame (11) has fastening structures (12) for a suspension device for suspending the machine, and wherein the upper screen stacks (3) rest directly or indirectly on the frame (11) and the lower screen stacks (4) are suspended directly or indirectly from the frame (11). Machine according to claim 7 or 8, wherein the frame accommodates electrical lines for supplying the electric motors of the drive modules (20). Machine according to one of the preceding claims, wherein the electric motors (51) of a plurality of the drive modules (20) are supplied by a common power stage (52).Machine according to one of the preceding claims, which is configured to move the flywheels in a direction opposite to a planned direction of rotation at start-up until they reach a mechanical stop, and only then to set them into a rotary motion in the planned direction of rotation. Machine according to claim 11, wherein the mechanical stop is formed by a pendulum element which, during a rotational movement of the flywheel in the intended direction of rotation, is deflected from a basic position to a deflected position, in which deflected position it does not impede the rotational movement. Machine according to any one of the preceding claims, wherein a rotational speed of the flywheels (23) is selectable and wherein the machine is configured so that the rotational speed can be read. Method for operating a machine according to any one of the preceding claims, wherein the flywheels of the drive modules are moved into a synchronous Rotary motion is set in motion, while a unit with the sieve stacks and the drive modules is mounted in such a way that it is capable of circular horizontal vibrations.

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