Method for controlling the damping of the movement of a press roller of a high-pressure roller press and corresponding high-pressure roller press

Abstract

Method for controlling the damping of the movement of a loose roller (3) of a high-pressure roller press (1), wherein the high-pressure roller press (1) has a hydraulic system (8) which presses the loose roller (3) against a fixed roller (2) and thus maintains a predetermined nip pressure in the nip (7) between the loose roller (3) and the fixed roller (2) when ground material passes through the nip (7) between the loose roller (3) and the fixed roller (2), characterized by the use of an adaptive damping control, which controls the damping of a mechanical oscillation movement of the idler roller, where the adaptive damping control performs the following control steps - Measuring mechanical vibrations on the machine frame (4) at least at one point and / or - measuring pressure fluctuations in the hydraulic system (8) at least at one point and / or - Measuring electrical current fluctuations in the electrical current consumption of at least one drive motor, wherein the at least one mechanical vibration and / or the pressure fluctuation and / or the current fluctuation enter into a control loop of the control system as at least one disturbance variable (13), - Performing a vibration analysis as a mathematical operation in a process computer, - Determine at least one damping constant from the result of the vibration analysis, - comparing the at least one damping constant with a predetermined damping constant, wherein the predetermined damping constant is entered into the control loop as a reference variable (11), - Setting at least one adjustable throttle (15, 16.1) in the hydraulic system (8), wherein the throttle position of the respective adjustable throttle (15, 16.1) is entered into the control loop as a manipulated variable (12), wherein the respective adjustable throttle (15, 16.1) in the hydraulic system (8) exerts a damping effect on the movement of the loose roller (3) and thus the control loop is closed.

Description

[0001] The invention relates to a method for controlling the damping of the movement of a floating roller of a high-pressure roller press. The high-pressure roller press has a hydraulic system that presses the floating roller against a fixed roller, thus maintaining a predetermined nip pressure in the nip between the floating roller and the fixed roller when grinding material passes through the nip between the floating roller and the fixed roller. The invention further relates to a high-pressure roller press having such a control system.

[0002] High-pressure roller presses are often used to crush or compact granular material. These presses consist of two counter-rotating, usually equally sized, rotatably mounted press rollers that rotate at the same peripheral speed and form a narrow roller gap between them. The material to be crushed or compacted is pulled through this roller gap, whereby the material is crushed or compacted under the high pressure prevailing in the roller gap. The result of this treatment, namely crushing or compacting, depends largely on the material properties of the material to be crushed. The crushing in the roller gap described here was first described as high-pressure crushing by Schönert et al. in the German laid-open application DE 27 08 053 ​​A1 and has since been considered a type of crushing method alongside grinding by shearing and crushing.

[0003] High-pressure roller presses differ fundamentally from other presses used for comminution. In particular, high-pressure roller presses designed for crushing rock are not comparable to roller presses used for crushing grain, for example. Grain rollers grind grain. Grain rollers weigh a maximum of 100 kg. The overall design of a grain roller differs significantly from high-pressure roller presses. Furthermore, grain rollers operate with a shearing action. High-pressure roller presses, on the other hand, operate without shearing.

[0004] High-pressure roller presses also differ significantly from strip rollers used for rolling steel. Steel strip rollers are characterized by their smooth running. The steel between the strip rollers is either very ductile, because the steel to be rolled is hot-formed, or the steel is cold-formable. Consequently, the running smoothness of a steel roller is quite high due to the nature of the rolling process. It is therefore possible to operate a strip roller with two rollers arranged horizontally one above the other, with the nip pressure being generated by the dead weight of the rollers or by hydraulic aids. Vibration problems are not to be expected due to the ductility of the steel being rolled. Depending on the steel being rolled, strip rollers can reach nip speeds of up to 200 km / h.Steel belt rolling is comparable to a cake dough roller rolling over raw pizza dough, spreading the dough, although the forces acting in a steel belt roller are many orders of magnitude greater. High-pressure roller presses for crushing ore and rock achieve roller gap speeds in the low double-digit km / h range at best. Due to their high rotational speed, belt rollers operate at a rotational frequency desirably far removed from the natural frequencies of their own structure. With high-pressure roller presses, which operate at much lower speeds, the desirable state of a natural frequency far removed from the roller rotational speed is not possible.

[0005] The present invention relates to high-pressure roller presses for comminuting brittle material to be ground, such as rock and ore. The brittleness of the material to be ground is a prerequisite for the suitability of this grinding process for the respective material to be ground. Belt rollers for steel operate at the opposite extreme of high-pressure roller presses, namely with ductile steel, which deforms beneath the roller and does not spontaneously crush due to brittleness, thus avoiding the pressure in the roller gap. In high-pressure roller presses, the rollers are arranged horizontally next to one another, forming a roller gap through which the material to be ground passes vertically. High-pressure roller presses have a roller gap pressure of 50 MPa and more.Due to the horizontal mounting of the rollers and the operation with brittle material, the overall mechanical behavior of the high-pressure roller press is not comparable to that of vertically stacked strip rollers, which, moreover, exhibit dampened and smooth running due to the ductility of the steel being rolled. In high-pressure roller presses, the grinding material passes through the roller gap, which is not always uniform, and the high pressure generated by hydraulic presses that move the rollers horizontally can cause a high-pressure roller press to vibrate. Vibration can occur even with slight changes in the grinding material properties. For example, dry, brittle grinding material can entrain air in the roller gap during comminution.If a significant amount of highly comminuted material is present in the roller gap, the air trapped in the material can escape spontaneously during compaction of the material before it spontaneously breaks down due to brittle cracks, thus yielding to the roller gap pressure. The vibration behavior of the high-pressure roller press can thus be influenced by nonlinear forces, the description of which eludes the consideration of the classical analysis of a damped vibration. Undesirably, the natural frequencies of high-pressure roller presses lie in the range of external excitation frequencies, such as the sudden yielding during brittle fracture, the spontaneous escape of air from the highly compacted material to be ground, the inherent rotation of the grinding rollers, and feeding by a bucket elevator.

[0006] In addition to the pressure in the roller gap, a number of parameters in the high-pressure roller press used for high-pressure comminution are crucial for optimal, energy-efficient, and low-wear comminution. For example, it is important that the rollers of the high-pressure roller press rotate without relative slippage, so that the rollers do not grind by shearing the material, but rather press it exclusively. Furthermore, it has been shown that the correct feed rate of fresh material per unit of time into the roller gap of the high-pressure roller press used also plays a significant role in the optimal function of the high-pressure roller press used.If the roller gap is fed with too little fresh material per unit of time, the high-pressure roller press operates as a crusher, especially when using rollers equipped with hard reinforcement elements, whereby the granular material to be crushed as fresh material is broken up by point loads. This type of crushing is less energy-efficient than high-pressure crushing and does not produce the desired fine product. If, on the other hand, the roller gap is fed with too much granular material as fresh material per unit of time, the ground material, consisting of fresh material and circulating material, becomes over-compacted in the roller gap, trapped air can no longer escape, and the roller gap of the high-pressure roller press used tends to become clogged.In this case, the resiliently mounted rollers deflect, the excess fresh material falls through the roller gap uncrushed, and the high-pressure roller press then returns to its previous state until it has to deflect repeatedly to allow the excess fresh material to pass through the roller gap. The roller press thus enters a first type of oscillatory motion, among other oscillatory movements, and begins to vibrate mechanically.

[0007] In addition to this type of mechanical vibration, which occurs when the rollers move back and forth in their flexible mountings at a frequency that is high compared to the moving masses, another vibrational movement exists within the high-pressure roller press in the form of an oscillating movement of the rollers, which is caused by the repetitive, braking effect of the overfilled roller gap on the rotating rollers. As a result of this rhythmic deceleration caused by an overfilled roller gap and renewed acceleration by the drive, the rollers enter a rotational vibration in which the torque and angular velocity of the rollers fluctuate evenly. This is particularly the case with driven rollers when a high-pressure roller press has only one driven roller with one idler roller.

[0008] Special types of oscillating movements can occur if the overload with too much fresh material occurs only in one part of the roll gap. The rolls can then exhibit a combined oscillation consisting of a back-and-forth movement of the rolls in a horizontal direction perpendicular to the extension of the roll gap and a rotational oscillation. The rolls can also undergo a slight, oscillating change of position, in which the respective roll rotates by very small angular amounts around a vertical axis. During this movement, the roll is not displaced evenly with both of its supporting bearing blocks; instead, the two bearing blocks at each end of a roll change their position alternately.

[0009] Mechanical vibration movements of very short duration and high frequency and amplitude in the form of an impact also occur when pieces of the fresh material that are too large pass through or when components that cannot be crushed by high-pressure treatment in the roller gap pass through, such as pieces of metal, i.e. hammer heads that are unintentionally found in the fresh material, large steel rivets or bolts, excavator teeth or other unwanted pieces of metal that can get into the fresh material during the extraction of the raw material.

[0010] Furthermore, mechanical vibrations can also occur within a high-pressure roller press during the start-up process if the ground material is not yet at equilibrium in circulation or if the circulating material has an unequilibrium composition. Finally, mechanical vibrations also occur when using fresh material that is wet and fine-grained.

[0011] If the frequency of one of the above-mentioned mechanical vibration movements happens to reach the frequency of a natural vibration of the high-pressure roller press, more energy is transferred to the entire system of the high-pressure roller press with each individual vibration movement, which can cause serious damage to the bearings, the roller surfaces and other components of the high-pressure roller press as a whole, not least because the rollers can reach a dead weight of over 50 t, larger rollers can even weigh 100 t, and an oscillating mass of this magnitude poses very great challenges even for very stable machine frames.

[0012] Naturally, the entire system of the high-pressure roller press is mechanically damped due to its design. This damping is provided, on the one hand, by the hydraulic system, in which the hydraulic fluid flows back and forth at high speed through the lines, which are thin compared to the diameters of the hydraulic rams or cylinders. The viscosity of the hydraulic fluid causes strong and rather linear damping as it flows through the lines at high speed. Linear damping can be described using the classic description of a damped oscillation. Furthermore, the movement of the bearing blocks on the slide rails of the floating rollers also absorbs a high level of mechanical energy in the form of friction, which dampens the oscillatory movement.The movement of the bearing blocks, however, does not follow linear damping, as the transition from static friction (no movement with slight surface deformation in the elastic range) to sliding friction occurs abruptly. Sliding friction also does not behave linearly. The resistance during sliding friction decreases with speed. Due to the multitude of possible vibrations, i.e. bending vibrations, torsional vibrations, vibrations damped by static / sliding friction, vibrations damped by the viscosity of the hydraulic fluid, and the multitude of external vibration excitations, such as periodic feeding of ground material by a bucket elevator, a large variety of different natural vibrations, i.e. different resonant frequencies, can be observed in a high-pressure roller press. The operating speed can also lead to vibratory movement if a bearing is running loose or if the rollers are radially out of alignment.

[0013] If the high-pressure roller press enters an unwanted vibration mode, it becomes apparent that the high-pressure roller press is no longer operating energy-efficiently and is also subjected to heavy mechanical stress.

[0014] In order to avoid or even prevent the formation of mechanical vibrations in the high-pressure roller press caused by overloading the roller gap with fresh material, the amount of fresh material fed in per unit of time can be controlled, for example by the feeding device feeding less fresh material into the roller gap per unit of time when undesired vibrations are detected in the high-pressure roller press. However, this has the disadvantage that a comparatively long follow-up time for the controlled system from the controlled feeding device until the vibrations are detected must be accepted. It takes a certain amount of time until the changed feeding of the roller gap with fresh material takes effect and the vibrations are ultimately reduced. By then, considerable damage to the high-pressure roller press may already have occurred or may have accumulated if this type of control intervention is required frequently.

[0015] The following state-of-the-art measures are known for monitoring the function of shredding devices: The publication US 2010 / 010 2152 A1 describes cone crushers equipped with proximity sensors, such as ultrasonic or laser sensors. By measuring the width of the exit gap, the gap width can be adjusted to the process conditions by raising or lowering the cone, thus avoiding uneven rotations that could damage the cone.

[0016] US 2004 / 025 5679 A1 describes a drum mill for crushing minerals, which has an acoustic sensor in the drum, with the help of which excessive loads on the drum, e.g. due to rock-like rock, can be detected.

[0017] DE 10 132 067 A1 discloses a method for acoustically monitoring hazardous operating conditions, such as slippage, in roller mills. For this purpose, the noises occurring in the roller mill, or rather the sound level, are recorded with a microphone, and the frequency spectrum is evaluated.

[0018] DE10 2011 018 705 A1 discloses a method for controlling the roll gap pressure depending on the observed vibration of the high-pressure roller press. Depending on the operating condition, the pressure in the hydraulic system is varied in order to always operate the high-pressure roller press close to its maximum pressure.

[0019] The German patent application DE 44 14 366 A1 also teaches reducing the hydraulic pressure when measured vibration amplitudes exceed a predetermined value over a certain period of time and, conversely, increasing the pressure when the predetermined vibration amplitudes are not exceeded.

[0020] German patent DE 196 47 483 B4 discloses a high-pressure roller press with a variable bladder accumulator in its hydraulic system, which absorbs pressure peaks in the hydraulic system. Pressure peaks are generated when material that cannot be crushed by brittle fracture passes through the heavy roller presses, forcing the press rollers to make sudden and very rapid evasive movements while opening the roller gap. Changing the gas volume of the bladder accumulator changes the spring constant of the buffer system and thus the pressure increase when the volume in the hydraulic system changes. Changing the gas volume in the bladder accumulator changes the stiffness of the spring system.

[0021] German patent application DE 10 2007 059 072 A1 teaches a high-pressure roller press with two idler rollers. In this high-pressure roller press, the roller gap pressure is also maintained via a hydraulic system that acts on the roller position. The specified location also teaches that in order to minimize the viscosity-related resistance of the pressure medium flowing through the lines, it is necessary to keep the flexible lines of the hydraulic system short. Since the roller gap position must be controlled when using two idler rollers, it is necessary for the entire system to operate with as little damping as possible to enable rapid adjustment of the roller gap position.

[0022] Patent application EP0320853A2 relates to a high-pressure roller mill for comminuting brittle material to be ground. Its central feature is an adaptive damping control system for the movable roller, which dampens longitudinal vibrations running transversely to the roller gap. A hydraulic throttle is used for this purpose, the damping effect of which is adjusted in real time to the vibration state of the roller. Control is achieved by means of a vibration measuring device, which changes the throttle effect via a controller, for example, an actuator or a switchable solenoid valve in a bypass line. This prevents the occurrence of resonant vibrations and enables stable operation of the mill even with changing material properties.

[0023] None of the publications disclose how these undesirable operating conditions associated with press roller vibration can be prevented or eliminated in advance, i.e., at the stage of their development. It would therefore be desirable if a high-pressure roller press could be operated in a controlled manner so that mechanical vibrational movements do not occur. The object of the invention is therefore to operate a generic high-pressure roller press in such a way that mechanical vibrational movements do not occur.

[0024] The object of the invention is achieved in that the high-pressure roller press has adaptive damping in the hydraulic system according to claim 1. A specific method for adaptive damping is specified in claims 2 to 6. A high-pressure roller having adaptive damping, consisting of a throttle in the hydraulic system and a corresponding control device, is specified in subclaims 7 to 12.

[0025] The special feature of this control system is that the high-pressure roller press can be operated at a constant hydraulic pressure despite the vibration control. This protects the hydraulic pump, which is not subjected to constant load changes, and allows the high-pressure roller press to operate in its ideal condition for more time, thus becoming more efficient.

[0026] The equation of motion of an oscillating system can be described by assuming harmonic oscillation behavior m*d2xdt+c*dxdt+k*x=0 with x equal to the position coordinate, t equal to the time, m equal to the moving mass, c equal to the damping coefficient and k equal to the restoring force.

[0027] All high-pressure roller presses described so far rely on a linear element to control or regulate vibration behavior. The linear element is the restoring force k in the aforementioned equation. To adaptively prevent the tendency to vibrate when vibration occurs, the restoring force is changed. Therefore, k in the equation of motion is changed.

[0028] Assuming that the moving mass of a press roll is and remains unchangeable, an alternative to intervening in the system, which obeys the previously mentioned equation of motion, or can at least be described by it to a good approximation, is to intervene in the damping constant c.

[0029] In order to avoid vibrations during operation of a high-pressure roller press, the idea of ​​the invention is to adjust the damping using a control loop so that when a vibration is detected, the settling behavior of the loose roller of a high-pressure roller press is such that the settling behavior corresponds as closely as possible to the aperiodic limiting case of a damped oscillator. A settling time or relaxation time is specified as the control element, within which the system has returned to a non-oscillating state after the occurrence of a forced vibration, for example when a component of the ground material that cannot be crushed by brittle fracture passes through it or when the composition of the ground material changes and / or the moisture content of the ground material changes. The forced vibration, which is calculated using vibration analysis, enters the system as a disturbance variable, and a damping element is entered into the control loop as the manipulated variable.The coupling path of the control loop is the path of the forced oscillation of the idler roll, which is to be avoided, and the damping of the idler roll's movement, both of which interact with each other. Since the idler roll can also be overdamped and, if damped too strongly, can enter the so-called and undesirable "creep mode," control is necessary. This not only prevents the creep mode detectable by vibration analysis, but also prevents the vibration that occurs if the damping is too low. Since the observable and undesirable natural frequency of the idler roll in a high-pressure roller press is close to its operating rotation frequency or close to its harmonics, a high-pressure roller press can easily excite itself into oscillating states during operation.Adaptive damping via the control system enables smooth operation of the high-pressure roller press, which operates outside the ideal operating parameter range of the roller gap with the shortest possible time. The ideal operating parameters are the rotational speed of the press rollers, the roller gap width, the roller gap pressure, and the grinding material flow as the ratio of the grinding material feed rate to time.

[0030] In the previously known control system for preventing vibration conditions in a high-pressure roller press, the ideal operating parameters are precisely those that are intervened in, namely the roller gap pressure, which can be adjusted via the hydraulic pressure and is proportionally related to it, and the roller gap width, which inevitably increases as the pressure drops. The average rotation frequency of the press roller can be assumed to be almost constant due to its large mass and the associated moment of inertia. The grinding material flow can also be assumed to be reasonably constant with appropriate control by a feeding device. However, the grinding material behavior is not sufficiently constant, particularly with regard to the tendency of the grinding material to entrap air, and the homogeneity of the grinding material. The largest average disturbance variables are therefore the variation in the grinding material properties, followed by the uniformity of the grinding material flow.These two disturbances cause the idler roll of a high-pressure roller press to vibrate itself due to rotation. Adaptive damping control is more suitable than previously known methods to minimize the time the roll gap pressure and geometry deviate from the ideal state.

[0031] The method described here for controlling the damping of the movement of a loose roller of a high-pressure roller press, wherein the high-pressure roller press has a hydraulic system which presses the loose roller against a fixed roller and thus maintains a predetermined nip pressure in the nip between the loose roller and the fixed roller when ground material passes through the nip between the loose roller and the fixed roller, can, in a specific embodiment of the method, have the following steps: measuring mechanical vibrations on the machine frame at at least one point and / or measuring pressure fluctuations in the hydraulic system at at least one point, and / or measuring electrical current fluctuations in the electrical current consumption of at least one drive motor as a first step, wherein the at least one mechanical vibration and / or the pressure fluctuation and / or the current fluctuation are entered into a control loop of the control system as at least one disturbance variable.After the measurement, a vibration analysis is performed as a mathematical operation in a process computer. Such vibration analyses can include low-pass filtering, high-pass filtering, or band-pass filtering. A Fourier transformation, particularly a fast Fourier transformation, can be performed. Statistical data smoothing methods, such as singular value decomposition, can be applied. Mathematical Gaussian convolutions and noise suppression systems can also be used. Finally, mathematical lock-in amplifier simulations can be used, in which the signals to be filtered are modulated with a periodic signal. The expert is free to choose an ideal vibration analysis.Once the vibration has been determined through vibration analysis, the next step is to determine at least one damping constant from the results of the vibration analysis. The damping constant is the constant before the first-order differential term in an equation of motion for a harmonic, damped oscillator. Given a known vibration behavior, this damping constant allows us to infer the expected settling behavior of the entire system. If the damping constant is too large, the idler roll of the high-pressure roller press to be controlled would tend toward undesirable creep, in which the high-pressure roller press operates outside of its ideal state and thus operates inefficiently, but still consumes energy.If the damping is too low, the idler roller of the high-pressure roller press would be prone to mechanical vibrations, which could cause severe damage to the high-pressure roller press, the foundation, and, in the worst case, to the surrounding area, such as cracks in structures due to vibrations transmitted through the ground to the foundation of a factory building. The next control step involves comparing at least one damping constant with a predetermined damping constant, with each predetermined damping constant being input into the control loop as a reference variable. The damping constant indirectly describes the settling time or relaxation time of the idler roller.The result of the comparison leads to the next control step, namely setting at least one adjustable throttle in the hydraulic system. The throttle position of the respective adjustable throttle is entered into the control loop as a manipulated variable, and the respective adjustable throttle in the hydraulic system exerts a damping effect on the movement of the idler roller, thus closing the control loop. The step of comparing the determined damping constant with the target damping constant can also be performed using a known PID control, a PI control, a PD control, or even an ID control, where P stands for "proportional," I for "integral," and d for "differential." This control strategy is well known to measurement and control engineers, and reference is made to the relevant specialist literature.

[0032] The previously described specific implementation is particularly suitable for controlling a high-pressure roller press system, in which a large number of forced vibration states can be measured. Unlike strip rollers, which, due to the nature of the rolling process with ductile steel, operate in a relatively quiet, i.e., low-vibration, state, high-pressure roller presses exhibit vibrations that originate, for example, from the following sources: higher-frequency vibrations due to the use of so-called "stud lining," i.e., the equipping of the surface of a press roller with a large number of hard particles; inhomogeneous grinding material properties; sudden brittle fracture of the grinding material to be ground; frequency converters with industry-typical 400 Hz alternating current with very high power consumption in the vicinity of the system (so-called mains hum); the same applies to 50 Hz or 60 Hz, depending on the existing mains frequency. Further vibrations may be generated by knocking bearings, the rotation of the press roller itself if it is worn out, and possiblyis no longer ideally cylindrical or is showing initial surface damage as a sign of wear. Finally, the machine frame exhibits various types of natural frequencies, be it bending vibrations of steel belts, torsional vibrations, or longitudinal vibrations. These vibrations can also occur as torsional vibrations of the shaft driving the idler roller at very high loads. Finally, unwanted bearing vibrations caused by gear meshing can also be found in the overall vibration pattern of a high-pressure roller press.

[0033] In order to filter out precisely the vibration required for control from the complex vibration spectrum and to ignore the vibrations that are unavoidable, for example high-frequency mains hum, bearing damage, rhythmic loading of the high-pressure roller press with ground material by a bucket elevator or undesirably rhythmic conveying of an overloaded conveyor belt, it is suitable to carry out a Fourier transformation (frequency transformation) for vibration analysis and to carry out the control only based on selected peaks in the frequency-transformed spectrum.A sequence of the following steps is suitable for structuring the vibration analysis: Fourier transforming the measured vibrations and / or pressure fluctuations and / or electrical current fluctuations; selecting predetermined linear combinations of individual frequency components from the Fourier-transformed vibrations; determining a damping constant for the individual Fourier-transformed vibrations from a time series of the frequency components; and feeding the damping constant back into a controller. The damping constant can be determined by regression, with the regression calculation being based on a linearized exponential function. Thus, an exponential coefficient of a decay curve is calculated using statistical methods. Here, too, reference is made to the relevant literature on statistical data analysis.

[0034] For data preparation, it is suitable to process the data from a measured oscillation diagram with a mathematical low-pass filter before the Fourier transformation.

[0035] Today's microcontrollers used in measurement and control units are capable of processing very complex and large amounts of data. To simplify data analysis, it can be advantageous to weight the determined damping constants and combine them into a weighted damping constant when controlling for a linear combination of specific vibration states ("Vibration 1 with frequency 1 is only relevant if vibration 2 with frequency 2 also occurs simultaneously"). This can be achieved by weighting the various damping constants and combining the weighted damping constants into a single value if more than one damping constant is determined.

[0036] A very special type of damping is achieved through the use of an adjustable throttle check valve in the hydraulic system. A throttle check valve is characterized by a fluid flow that is evenly throttled in both directions, with the strength of the throttling effect being adjustable using an actuator. However, a check valve is located parallel to the throttle. The check valve opens to flow in a first direction and closes to flow in a second, opposite direction.The use of a throttle check valve, which is installed in the hydraulic system in such a way that the floating roller can move freely away from the fixed roller with virtually no additional throttle damping and only against the restoring force of a bladder accumulator in the hydraulic system (undamped), but can only move back to the fixed roller with damping, allows the settling time (relaxation time) of the floating roller to be significantly shortened, thus further improving the damping effect. While the throttle check valve introduces a strong nonlinear term into the equation of motion that describes the movement of the floating roller, this nonlinear term makes the analytical description and calculation of the settling time almost impossible.For a control system, however, the underlying mathematical model is irrelevant if only the relaxation time, which is determined by the number of zero crossings of the movement and the time required for this, is used as a measure for the damping constant.

[0037] Due to the constant pressure control of the high-pressure roller press, it is necessary for the hydraulic system to have an off switch and / or the idler roller to have a stop to prevent the idler roller from coming into direct contact with the fixed roller when idling. If the rollers touch each other under pressure, this can more easily cause damage to the surface reinforcement with hard particles. To make the high-pressure roller insensitive to unwanted idling, the hydraulic system can be provided with an automatic pressure cut-off, which is triggered when the idler roller comes closer than a predetermined distance to the fixed roller. A mechanical switch on the machine frame detects the approach of the idler roller to the fixed roller. A similar result can also be achieved with a mechanical stop.

[0038] The invention is explained in more detail with reference to the following figures. They show: Fig. 1 a high-pressure roller press with locations of exemplary strain gauges, Fig. 2 an exemplary, unprocessed vibration diagram of a vibration detector, Fig. 3 that vibration diagram from Fig. 2 after processing by a low-pass filter, Fig. 4 the edited vibration diagram Fig. 3 after Fourier transformation, Fig. 5 Selecting a Fourier coefficient from Fig. 4 as a representation over time, Fig. 6 Representation of a Fourier series from Fig. 4, which is selected via a threshold, Fig. 7 an inverse transformation of the selected Fourier series from Fig. 6, Fig. 8 Illustration of the effect of insufficient (too low) damping on the vibration behavior of the idler roller, Fig. 9 Illustration of the effect of ideal (optimal) damping on the vibration behavior of the idler roller, Fig. 10 Illustration of the effect of excessive damping on the vibration behavior of the idler roller, Fig. 11 a high-pressure roller press with hydraulic system from the STATE OF THE ART Fig. 12 an embodiment of the high-pressure roller press according to the invention with the maximum number of vibration sensors and an optional throttle check valve, Fig. 13 Repetition of the figures Fig. 8, Fig. 9 and Fig. 10, which occur when using an adjustable throttle, for comparison with comparable diagrams, when using a throttle check valve in Fig. 14, Fig. 14 diagrams from figures Fig. 8, Fig. 9 and Fig. 10, but when using a throttle check valve.

[0039] In Fig. Figure 1 shows a generic high-pressure roller press 1, which has two counter-rotating press rollers as a fixed roller 2 and a loose roller 3, which are housed in a machine frame 4, which in turn is equipped with sensors 20 at different positions for detecting oscillatory movements. The two press rollers, fixed roller 2 and loose roller 3 of the high-pressure roller press 1, are pressed against one another via hydraulic rams 17 and 18, but without touching one another. By means of a feeding device (not shown here), the material to be ground is fed into the roller gap 7 of the high-pressure roller press 1 between the fixed roller 2 and the loose roller 3 and is thereby ground by the pressure prevailing between the two rotating press rollers, fixed roller 2 and the loose roller 3. The ground material is ground by brittle fracture, avoiding any shearing stress.Strain gauges 20 are mounted at various points on the machine frame 4 of the high-pressure roller press 1 as sensors for detecting vibrational movements. The vibrations measured by the strain gauges 20 are transmitted to an evaluation device (not shown here), where the amplitude and / or frequency of the measured vibrational movement is compared with a predetermined target value. If the amplitude exceeds a critical value at a predetermined frequency, which is determined by a Fourier transformation or, more generally, by frequency filtering, the position of a throttle valve (not shown in this drawing) is changed, thereby increasing the damping of the movement.When the intensity of the oscillation movement falls below the previously determined critical range due to the increase in the damping effect of the throttle valve, the damping is slowly reduced again using a control strategy, preferably according to the PID method, so that the roller press 1 always operates in a damping range that brings the mechanical oscillation movement of the loose roller as close as possible to the aperiodic limiting case of damped oscillation. Since the entire system of the high-pressure roller press 1, with the not necessarily linear damping of the movement of the bearing blocks in the machine frame 4, cannot be fully described by an equation of motion for a damped harmonic oscillation, the control strategy pursues damping that corresponds as closely as possible to the movement pattern of the aperiodic limiting case with an initial deflection in a first direction, a return with slight overshoot and a slow approach to the zero position.

[0040] In Fig. Figure 2 shows, by way of example, a vibration diagram as F1(t) (function 1 over time t), which could have been recorded by almost any motion sensor. The abscissa shows the mechanical displacement D, and the ordinate shows time t. The following sensors are particularly suitable for measuring vibration: strain gauges 20 at various locations on the machine frame 4. Strain gauges 20 can measure longitudinal vibrations of a metal belt of the machine frame 4, as well as torsional vibrations of a drive shaft. Acceleration sensors at just as many locations on the machine frame 4 can measure bending vibrations of the corresponding metal belt when it vibrates like a guitar string. Although the spatially resolved amplitude of this vibration is very small, usually in the range of a few µm, it is sufficient to measure characteristic vibrations.Acceleration sensors can also measure when the entire high-pressure roller press 1 performs a corresponding counter-movement in space due to the back-and-forth oscillating idler roller 3. Other suitable measurement sources include the pressure recording in the hydraulic system 8 and the measurement of the current consumption of the drive motors. Each vibration source has its own typical superposition of negligible vibrations, such as the very strong mains frequency or converter frequency when measuring current consumption, the rotation frequency and its harmonics when measuring accelerations using acceleration sensors, and again the mains frequency when measuring longitudinal vibrations, and the frequency that arises from the brittle fracture of the ground material, more as gray noise, i.e., not Gaussian noise with hard signal peaks. An acceleration sensor directly on a bearing block will detect an actual vibration of the idler roller as the dominant vibration.The aim of the invention is to regulate the damping state with detected vibrations before the high-amplitude back and forth movements of the loose roller 3 occur.

[0041] For initial signal conditioning, the signal can be subjected to low-pass filtering, which suppresses gray noise and the mains frequency. The result of the low-pass filtering is shown in Fig. 3 the low-pass filtered signal of the displacement-time diagram Fig. 2 is shown as F2(t) (function 2 at time t). Essentially, two oscillations of different frequencies are visible here: a dominant fundamental oscillation and a harmonic, along with traces of higher harmonics.

[0042] In Fig. Figure 4 shows the Fourier transform, which can be understood as a frequency filtering of a signal in parallel channels a)... b) ... n). The Fourier transform converts the signal from Fig. 3 into a frequency-time diagram, where the frequency from channel a) is a function F a (f,t) (function a) with respect to frequency f and time t), channel b) as a function F b (f,t) (function b) with respect to frequency f and time t) and channel n) as a function F n (f,t) (function n) with respect to frequency f and time t).

[0043] The dominant oscillation in channel a) is selected here and is in Fig. 5 as a plot of a) over time t. The coefficient x(a) of the damping part e -(x(a)*t) The vibration is suitable for regression analysis to determine a damping coefficient with which the damping control can be carried out. A regression analysis of the time course of the coefficient F a(f, t) allows a value x(a) to be determined assuming a negative-exponential curve. It has been observed in the invention that the oscillation of the floating roller 3, which is to be prevented, can be detected early on by typical frequency patterns that are found in the natural vibration frequencies of the machine frame of the high-pressure press. Even very strong, solid steel belts of a machine frame of a high-pressure roller press already exhibit very strong, machine-frame-specific vibration patterns clearly before any oscillation of the floating roller 3 occurs. To detect this pattern, it is only necessary to monitor a high-pressure roller press 1 with a sensitive vibration analysis and to identify the vibration patterns shortly before the floating roller vibration to be avoided occurs.This can be done using common statistical methods, namely temporal correlation analysis, but it is also possible for a skilled person to recognize the pattern with the naked eye. Once the pattern has been recognized, it can be programmed into the control system as a typical, machine-frame-specific pattern.

[0044] Depending on the observed oscillation pattern, it is possible to select different coefficients after the Fourier transformation. In the simplest case, it is also possible to define a threshold and identify all coefficients that exceed the threshold as the dominant oscillation component. This procedure is described in Fig. 6, in which the coefficients a) and b) exceed a threshold value in C (coefficient). An inverse transformation of these Fourier coefficients shows that a dominant and a higher harmonic oscillation with different phase positions in this example are present according to the distance from the natural frequency. The two inversely transformed oscillations are shown in Fig. 7 shown.

[0045] In Fig. In Figure 7, the upper oscillation is represented as the displacement D of the frequency with coefficient a) over time t). The lower oscillation diagram shows the displacement D of the frequency with coefficient b) over time t.

[0046] The control strategy now determines from the decay of the oscillation in, for example, Fig. 7 via a continuous signal ( Fig. 5) a coefficient x(a) for the damping of the equation of motion for a telltale vibration in the machine frame 4 of a high-pressure roller press 1. This signal is the feedback signal to the control loop. If the damping is too strong, and thus the coefficient x(a) is too large, the damping of the movement of the idler roller 3 is reduced by partially opening a throttle valve of a throttle in the hydraulic system 8 of a high-pressure roller press 1, and vice versa. The different control states are shown in Figures Fig. 8 (damping too low), Fig. 9 (damping ideal) and Fig. 10 (damping too high). If the damping is too low, the idler roller 3 can only settle after several vibration cycles in the event of an externally imposed vibration, for example, by rotation of the idler roller 3 at a predetermined speed, a roller gap pressure determined for this speed, which is proportional to the hydraulic pressure of the hydraulic rams 17 and 18, and an inappropriate material property of the ground material. If a 100 t roller oscillates back and forth at a frequency significantly greater than 1 Hz, the resulting shocks transmitted to the ground can cause damage in the immediate vicinity. It has already been observed that an improperly operated and unmonitored high-pressure roller press has caused cracks in the foundation of a nearby industrial building. This situation must be avoided at all costs. If the damping is too high, the high-pressure roller press 1 will run smoothly. The resulting creep ( Fig. 10), in which after deflection of the idler roller 3, it only slowly returns to the ideal operating point at D = 0, means that the high-pressure roller press is operating inefficiently for this time. The roller gap is too large and passing material is not crushed, but at most broken into large pieces. The hatched area under the curve in Fig. 10 shows the displacement over time. The larger the displacement D, the less efficient the high-pressure roller press 1 operates. Fig. 9 shows how the idler roller 3, after a deflection, for example due to the passage of an excavator tooth or the passage of an oversized piece of ground material, already after a short time of a single overshoot at time t max is back in equilibrium and thus at the ideal operating point.

[0047] In Fig. 11 shows a high-pressure roller press from the PRIOR ART, comprising a fixed roller 2 and a loose roller 3. The loose roller 3 is pressed against the fixed roller 2 by hydraulic rams 17 and 18. Hydraulic fluid from a reservoir 23 is pumped into the pistons of the hydraulic rams 17 and 18 by means of a hydraulic pump 19 to exert force. In order to compensate for sudden load peaks (passage of an excavator tooth, a piece of metal, an overly large piece of ground material), a bladder accumulator 14 is provided which has a pressurized air cushion against which the hydraulic fluid can expand when it is pushed in pulses out of the pistons of the hydraulic rams 17 and 18 back into the line system of the hydraulic system by a jerky movement of the loose roller 3.

[0048] In Fig. Figure 12 shows an embodiment of the high-pressure roller press according to the invention. The essential element here is an adjustable throttle 15 or an adjustable throttle check valve 16 between the hydraulic system 8 and the bladder accumulator 14. The throttle 15 or the throttle check valve 16 can dampen the movement of the idler roller 3 at a constant working pressure in the roller gap 7. If a throttle check valve 16 is used, hydraulic fluid can flow quickly and undamped through the bypass 16.2 towards the bladder accumulator 14 and expand there in the event of a sudden displacement of the idler roller 3. However, the return flow from the pressurized bladder accumulator 14 is dampened by the throttle 16.1 because the free cross-section for the flow of the hydraulic fluid is limited by the throttle 16.1. The viscosity of the hydraulic fluid thus generates a counterforce that opposes the flow velocity of the hydraulic fluid.The high-pressure roller press 1 has various vibration sensors, each generating an individual vibration diagram as a disturbance variable 13. These sensors include strain gauges 20 at various locations on the machine frame 4, acceleration sensors at these same locations, a digital pressure gauge 21 in the hydraulic system 8 for detecting pressure fluctuations, and a digital ammeter 22 for detecting vibrations in the current consumption of the electric drive motors. All of these sensors provide a vibration diagram that can be processed as previously described. From a determined damping coefficient, which represents the vibration behavior of the idler roller 3, the control device determines a control value for the throttle 16.1, for example, using the PID control strategy. The throttle 16.1 influences the vibration behavior of the idler roller 3, thus closing the control loop.In this example of a high-pressure roller press 1, a position switch 24 is provided to prevent the loose roller 3 from contacting the fixed roller 2 under pressure. If the loose roller 3 comes too close to the fixed roller 2, the position switch 24 shuts off the hydraulic pump 19 to prevent damage to the hard body reinforcement (pattern on the press rollers, loose roller 3 and fixed roller 2, consisting of rectangles).

[0049] In the figures Fig. 13 and Fig. 14 shows the different effects of a throttle 15 and a throttle check valve 16 on the settling time (relaxation time) of the loose roller 3. Fig. 13 is merely a repetition of the figures Fig. 8, Fig. 9 and Fig. 10. In Fig. 14 shows in the middle example that a throttle check valve 16 leads to a significant shortening of the settling time (relaxation time) t max to t max, neuIn the event of an evasive movement, the idler roller 3 can retract without or with little damping, opening the roller gap 7, which is shown in the middle diagram of Fig.14 is shown with an arrow in bold on the far left pointing to the right. The bold arrow represents a fast and unrestrained or undamped movement. During this return movement, the check valve 16.2 is open and hydraulic fluid flows through the bypass, the check valve 16.2 past the throttle 16.1. During the forward movement of the idler roller 3 towards the fixed roller 2, the check valve 16.2 is closed and the hydraulic fluid from the bladder accumulator 14 must take the path through the throttle 16.1. Due to the throttle 16.1, the return movement of the idler roller 3 is slower due to the pressure in the bladder accumulator 14 and with damping, represented by an arrow to the left (not in bold), which represents a slower movement due to stronger damping. Considerable kinetic energy is dissipated in the process. The overshoot amplitude behaves for the period of the return almost as in the case with only one throttle 15 without a bypass / check valve 16.2.As soon as the reversal point is reached during the overshoot, the idler roller 3 moves back to its ideal position without damping (right, bold arrow pointing to the right) due to the force of the compacted ground material. The return is faster when using a throttle check valve 16 than with damping in both directions with a throttle 15 acting equally in both flow directions. The rapid movement in one direction shortens the settling time (relaxation time) t. max, neusignificantly shorter, so that the high-pressure roller press 1 is only operated outside of its optimal operating point for a very short period of time. It should be noted at this point that the introduction of a throttle check valve introduces a strong anharmonic component into the motion system of the loose roller 3, which can lead to stronger harmonics in the equation of motion, and thus stronger jerk moments (third derivative of position with respect to time in an equation of motion) can occur, which can travel through the ground as shock waves and have an effect in undesirable locations. However, a major advantage of the invention is that the vibration analysis controls the adaptive damping in such a way that the shocks occur only to a greatly reduced extent.However, the unavoidable impact that occurs, for example, when an excavator tooth passes through the roller gap is accompanied by significantly lower shock wave transmission to the soil due to the unbraked or undamped evasive movement of the idler roller 3 than with a movement damped in both directions. Thus, the strong impacts into the soil or the machine frame are attenuated, but the avoided rhythmic anharmonic vibration components are amplified. Since the stronger vibration components are compensated for from the outset, the damping method offers advantages across the entire range of applications. LIST OF REFERENCE SYMBOLS 1 high-pressure roller press 2 fixed rollers 3 Loose roller 4 machine frames 7 Roller gap 8 Hydraulic system 10 controllers 11 Leading variable 12 Control variable 13 Disturbance 14 bladder storage 15 Throttle, adjustable 16 Adjustable throttle check valve 16.1 Throttle, adjustable 16.2 Bypass, check valve 17 hydraulic rams 18 hydraulic rams 19 Hydraulic pump 20 strain gauges 21 digital pressure gauge 22 digital ammeter 23 storage 24 position switches 30 Vibration diagram 31 Fourier transformation a time series b time series D Deflection C coefficient the base of the natural logarithm p pressure t time tmax settling time (relaxation time) t max, neu shortened settling time, shortened relaxation time f frequency F Function of

Claims

[1] Method for controlling the damping of the movement of a loose roll (3) of a high-pressure roll press (1), wherein the high-pressure roller press (1) has a hydraulic system (8) which presses the loose roller (3) against a fixed roller (2) and thus maintains a predetermined roller gap pressure in the roller gap (7) between the loose roller (3) and the fixed roller (2) when regrind passes through the roller gap (7) between the loose roller (3) and the fixed roller (2), characterized by the use of an adaptive damping control system, which controls the damping of a mechanical oscillating movement of the loose roller, the adaptive damping control performs the following control steps - Measuring mechanical vibrations on the machine frame (4) at at least one point and / or - Measuring pressure fluctuations in the hydraulic system (8) at at least one point and / or - Measuring electrical current fluctuations in the electrical current consumption of at least one drive motor, wherein at least one mechanical vibration and / or pressure fluctuation and / or current fluctuation is entered as at least one disturbance variable (13) into a control loop of the control system, - Performing a vibration analysis as a mathematical operation in a process computer, - Determine at least one damping constant from the result of the vibration analysis, - Comparing the at least one damping constant with each predetermined damping constant, wherein each predetermined damping constant is entered into the control loop as a reference variable (11), - Positioning at least one adjustable throttle (15, 16.1) in the hydraulic system (8), wherein the throttle position of the respective adjustable throttle (15, 16.1) is entered into the control loop as a manipulated variable (12), wherein the respective adjustable throttle (15, 16.1) in the hydraulic system (8) exerts a damping effect on the movement of the loose roller (3) and thus the control loop is closed. [2] Method according to claim 1, characterized by the use of a check valve (16.2) in parallel to the adjustable throttle (16.1), which is connected to the hydraulic system in such a way that - a movement of the loose roller (3) while opening the roller gap (7) allows hydraulic fluid to pass through the assembly of throttle (16.1) and check valve (16.2) and - a movement of the loose roller (3) under narrowing of the roller gap (7) allows hydraulic fluid to pass only through the adjustable throttle (16.1). [3] Method according to one of claims 1 or 2, characterized by a sequence of the following steps in vibration analysis - Fourier transforming the measured vibrations and / or pressure fluctuations and / or electrical current fluctuations, - Selecting predetermined linear combinations of individual frequency components from the Fourier-transformed oscillations, - Determining a damping constant for the individual Fourier-transformed oscillations from a time series of the frequency components, - Feeding the damping constants back into a controller (10). [4] Method according to any one of claims 1 to 3, characterized by - Low-pass filters for the measured vibrations and / or pressure fluctuations and / or electrical current fluctuations before the Fourier transform step. [5] Method according to any one of claims 1 to 3, characterized by - Weights of the different damping constants, - Combine the weighted damping constants into one value if more than one damping constant is determined. [6] High-pressure roller press (1), comprising - at least one fixed roller (2), and - at least one loose roller (3), wherein the high-pressure roller press (1) has a hydraulic system (8) which presses each loose roller (3) assigned to a fixed roller (2) against the assigned fixed roller (2) and thus maintains a predetermined roller gap pressure in the roller gap (7) between the loose roller (3) and the fixed roller (2) when ground material passes through the roller gap (7) between the loose roller (3) and the fixed roller (2), characterized by , that an adaptive damping control according to one of claims 1 to 5 controls the mechanical vibration movement of the loose roller. [7] High-pressure roller press according to claim 6, comprising characterized by, that an adjustable throttle (15, 16.1) is present in the hydraulic system (8), which can be adjusted via a controller (10) to regulate the damping of the fluid flow in the hydraulic system (8). [8] High-pressure roller press according to one of claims 6 or 7, characterized by , that the hydraulic system (8) maintains a constant pressure (p). [9] High-pressure roller press according to one of claims 6 to 8, characterized by , that the hydraulic system (8) has an automatic pressure cut-off which is triggered when the loose roller (3) comes closer to the fixed roller (2) than a predetermined value, wherein a mechanical switch (24) on the machine frame (4) detects the approach of the loose roller (3) to the fixed roller (2) and / or that the high-pressure roller press has a mechanical stop for the loose roller which prevents the loose roller from touching the fixed roller under pressure. [10] High-pressure roller press according to one of claims 8 to 10, characterized by, that the controller (10) operates according to claims 1 to 5. [11] High-pressure roller press according to any one of claims 6 to 10, characterized by , that the hydraulic system (8) is buffered by a bladder accumulator (14) which is connected to the hydraulic system (8) via the adjustable throttle (15, 16.1). [12] High-pressure roller press according to one of claims 7 to 11, characterized by , that the adjustable throttle (16.1) has a check valve, so that it is a throttle check valve.

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