Gap width monitoring

Abstract

This disclosure relates to a method for monitoring the width (w) of a gap (1) between two grinding discs (2) in a grinding apparatus (10) for processing fibrous fluid (6). The method includes rotating a first grinding disc about a rotation axis of a first disc relative to a second grinding disc. The method also includes obtaining a spectrum of mechanical vibrations in the grinding apparatus caused by the rotation of the first disc relative to the second disc. The method further includes determining the frequency of vibration peaks within a predetermined frequency range of the obtained spectrum, the frequency of which is an indication of the gap width.

Description

Technical Field

[0001] This disclosure relates to monitoring the gap width between two grinding discs in a grinding apparatus used for processing fibrous fluids. Background Technology

[0002] In the paper industry, equipment such as dispersers, refiners, and dewatering machines are used to process slurries in the form of liquid dispersions. The fluid slurry is pressed between two grinding discs that rotate relative to each other around a rotational axis. The gap width between the discs, i.e., the axial distance between the discs, affects the processing efficiency. Therefore, an appropriate gap width needs to be set during operation.

[0003] Traditionally, before operation, a suitable gap width is set by axially pushing the grinding discs together as they rotate. The resulting sound, heard by the operator, defines the zero or minimum gap width. From this minimum value, the discs can be axially separated by the desired amount, after which grinding can begin. A drawback is that the gap width is not monitored during operation, and periodic interruptions are required for recalibration to find the minimum. Recalibration is often necessary because the grinding discs wear down during operation, affecting the minimum value and processing efficiency at a given gap width.

[0004] US2022 / 0098790 discloses a slurry grinding apparatus in which, in order to determine the minimum distance between substrates, mechanical vibration is detected on the apparatus, and the distance between substrates rotating relative to each other is reduced until the frequency and / or amplitude of the vibration and / or the frequency variation and / or amplitude variation exceed a limit value.

[0005] WO2022 / 043363 discloses sensing vibrations caused by relative rotation of two processing tools with a processing gap between them. The vibration intensity in the frequency range of 5-12 kHz is measured over time. When the vibration intensity exceeds a threshold, this indicates that the processing tools are in contact with each other, and the processing gap can be increased to prevent further such contact. To avoid false positives, intensity measurements can be performed at several consecutive time intervals.

[0006] US2007 / 125891 similarly discloses the measurement of axial vibration of a slurry mill over time. When the measured vibration indicator plates are colliding, the slurry flow rate increases or the plates further separate. Summary of the Invention

[0007] One object of the present invention is to monitor the gap width of a grinding device during operation.

[0008] According to one aspect of the invention, a method is provided for monitoring the gap width between two grinding discs in a grinding apparatus for processing fibrous fluid. The method includes rotating a first grinding disc about a rotation axis of a first disc relative to a second grinding disc. The method further includes obtaining a spectrum of mechanical vibrations in the grinding apparatus caused by the rotation of the first disc relative to the second disc. The method also includes determining the prevalence of vibration peaks within a predetermined frequency range of the obtained spectrum, the prevalence being an indication of the gap width.

[0009] According to another aspect of the invention, a controller is provided, comprising processing circuitry and a storage device storing instructions executable by the processing circuitry, thereby enabling the controller to perform embodiments of the methods disclosed herein.

[0010] According to another aspect of the present invention, a grinding apparatus is provided, which includes an embodiment of the controller disclosed herein, as well as a first grinding disc and a second grinding disc.

[0011] According to another aspect of the present invention, a computer program product is provided, the computer program product including a computer executable component, which, when the computer executable component is run on processing circuitry included in a controller, enables the controller to perform embodiments of the methods disclosed herein.

[0012] By obtaining the spectrum of mechanical vibration and determining the occurrence rate of vibration peaks in the spectrum, in the frequency domain, for example, determining how many peaks with a predetermined vibration amplitude (energy) exist within a predetermined frequency range of the spectrum, an indication of the gap width is provided. A smaller gap width results in a higher occurrence rate of vibration peaks, indicating a more difficult processing of fibrous fluids (e.g., slurries). The expected occurrence rate of vibration peaks can be known, for example, from previous operation of the grinding equipment, typically using the same type of grinding disc.

[0013] By studying vibration peaks in the frequency domain rather than the time domain, the gap width can be monitored, not just whether the discs are in contact (colliding). According to the invention, the occurrence rate of vibration peaks in the frequency domain of the spectrum is determined. For example, the occurrence rate can be defined by the number of vibration peaks within a predetermined frequency range of the spectrum, or by the average distance between adjacent vibration peaks within that frequency range. Therefore, the occurrence rate can be considered as the density of vibration peaks at various frequencies in the spectrum.

[0014] It should be noted that any feature of any aspect may be applied to any other aspect (where applicable). Similarly, any advantage of any aspect may be applied to any other aspect. Other objects, features, and advantages of the appended embodiments will become apparent from the following detailed disclosure, the appended dependent claims, and the accompanying drawings.

[0015] Generally, all terms used in the claims should be interpreted according to their ordinary meaning in the technical field, unless otherwise expressly defined herein. Unless otherwise expressly stated, all references to “a / an / the element, device, component, apparatus, step, etc.” should be interpreted as referring to at least one instance of that element, device, component, apparatus, step, etc. Unless expressly stated otherwise, the steps of any method disclosed herein need not be performed in the exact order disclosed. The use of “first,” “second,” etc., for different features / components of this disclosure is intended only to distinguish these features / components from other similar features / components, and not to assign any order or hierarchy to these features / components. Attached Figure Description

[0016] Embodiments will be described by way of example with reference to the accompanying drawings, wherein:

[0017] Figure 1 This is a schematic side view of a longitudinal section of a grinding apparatus according to some embodiments of the present invention.

[0018] Figure 2 This is a schematic block diagram of a grinding apparatus according to some embodiments of the present invention.

[0019] Figure 3 This is a schematic block diagram of a controller according to some embodiments of the present invention.

[0020] Figure 4 This is a schematic flowchart illustrating some embodiments of the method of the present invention.

[0021] Figure 5 These are illustrative examples of the spectrum and occurrence rate of vibration peaks of mechanical vibration according to some embodiments of the present invention.

[0022] Figure 6 This is a schematic diagram illustrating an example of the occurrence rate of vibration peaks as a function of gap width according to some embodiments of the present invention. Detailed Implementation

[0023] The embodiments will now be described more fully with reference to the accompanying drawings, in which some embodiments are illustrated. However, many other embodiments of different forms are possible within the scope of this disclosure. Rather, the following embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of this disclosure to those skilled in the art. Throughout the description, the same reference numerals refer to the same elements.

[0024] Figure 1The illustration shows a grinding apparatus 10, such as a disperser, mill, or degreasing machine. The grinding apparatus is configured to process fibrous fluids, such as liquids in which fibers are suspended (i.e., liquid suspensions), such as pulps or bio-pulps used in papermaking. In the case of pulps, the fibrous fluid may include cellulose fibers. Thus, in some embodiments, the fibers in the fibrous fluid comprise cellulose or are composed of cellulose.

[0025] The grinding apparatus 10 includes a first grinding disc 2a and a second grinding disc 2b, which are arranged to rotate relative to each other about a rotation axis 5. Typically, the first grinding disc 2a and the second grinding disc 2b are arranged in corresponding parallel planes, and each grinding disc is arranged to be rotationally symmetrical about a line of symmetry corresponding to the rotation axis 5. For example, the first grinding disc 2a may be included (e.g., mounted) in a rotor 3a arranged to rotate about the rotation axis 5, while the second grinding disc 2b may be included (e.g., mounted) in a stator 3b arranged to remain stationary when the rotor 3a rotates. A gap 1 is formed between the first disc 2a and the second disc 2b, the gap width w being defined by the axial distance between the discs (or between the corresponding parallel planes of the disc arrangement). During operation, as the grinding discs 2a and 2b rotate relative to each other, the fiber fluid 6 is compressed through the gap 1 between the grinding discs 2a and 2b and is thus processed. For example, as shown in the figure, the fiber fluid 6 can be introduced into the gap 1 from, for example, an axial inlet formed in the stator 3b, so that when the fluid 6 flows from the axial inlet to the periphery of the grinding disc, the fluid 6 is processed by the grinding discs 2a and 2b in the gap 1, as indicated by the arrow in the gap 1 in the figure.

[0026] The clearance width w can be adjusted by axially shifting at least one of the grinding discs 2a and 2b, for example, by moving the rotor 2a axially toward the stator 2b to decrease the clearance width w, or moving it away from the stator 2b to increase the clearance width w. However, the actual clearance width w (i.e., the distance between the discs, in millimeters or other units of length) can be difficult to know based solely on the axial position of the rotor 3a, for example, because the thickness of the grinding discs 2a and 2b can vary due to design or wear.

[0027] Figure 2 The illustration shows a grinding apparatus 10, for example, according to Figure 1The grinding apparatus 10 includes a vibration sensor 22 for sensing mechanical vibrations generated by the rotation of the discs relative to each other. The vibration sensor 22 allows the acquisition of a vibration spectrum. The vibration sensor may include an accelerometer, but any other vibration sensor, such as a laser vibrometer, may be used additionally or alternatively. The grinding apparatus 10 may include a housing 21 that at least partially surrounds a first grinding disc 2a and a second grinding disc 2b, for example, at least partially surrounding a rotor 2a and a stator 2b. Mechanical vibrations generated by the rotation of the discs relative to each other, for example, when fluid 6 is compressed through gap 1, can propagate to the housing. Therefore, the vibration sensor 22 can be conveniently arranged to sense vibrations in the housing 21, for example, by being mounted on the housing 21, especially if the vibration sensor 22 includes an accelerometer.

[0028] The grinding apparatus 10 may also include a controller 20 for controlling the operation of the grinding apparatus. In some embodiments, the controller 20 controls the rotational speed of the grinding discs (one or more) and any axial displacement of the grinding discs (one or more). The controller 20 may, for example, send control signals to cause the first disc 2a to rotate about its axis of rotation 5. For example, the controller 20 may receive a signal 23 from a sensor 22, from which the controller 22 may obtain a spectrum. Based on the vibration spectrum, the controller may also determine the occurrence rate of vibration peaks. In some embodiments, the controller may control a user interface, for example for communicating with or presenting information to a user / operator (e.g., a human user) of the grinding apparatus 10.

[0029] Figure 3 The diagram illustrates a controller 20. The controller 20 includes processing circuitry 31, such as a central processing unit (CPU). Processing circuitry 31 may include processing units in the form of one or more microprocessors. However, other suitable devices with computing capabilities may be included in processing circuitry 31, such as application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or complex programmable logic devices (CPLDs). Processing circuitry 31 is configured to run one or more computer programs or software (SW) 33 stored in a storage device 32 containing one or more storage units (e.g., memory). Storage units are considered computer-readable devices 32, forming a computer program product as a computer-executable component together with the SW 33 stored thereon, and may be, for example, in the form of random access memory (RAM), flash memory or other solid-state storage, or a hard disk, or a combination thereof. Processing circuitry 31 may also be configured to store data in storage device 32 as needed. The controller 20 may also include a communication interface 23, for example for receiving sensor signals 23 from a vibration sensor 22.

[0030] Figure 4 Some embodiments of the method disclosed herein are illustrated. The method is used to monitor the width w of a gap 1 between two grinding discs 2 in a grinding apparatus 10 for processing fibrous fluid 6. The method includes rotating the first disc 2a of the grinding disc about a rotation axis 5 of the first disc relative to a second disc 2b of the grinding disc S1. The method also includes obtaining a spectrum 50 of mechanical vibrations in the grinding apparatus 10 caused by the rotation S1 of the first disc 2a relative to the second disc 2b. The method further includes determining, within a predetermined frequency range 52 of the obtained spectrum 50 of S2, the occurrence rate of a vibration peak 54, which is an indication of the gap width w. In some embodiments of the invention, the method further includes shifting, S4, at least one of the first disc and the second disc 2 along the rotation axis 5 during rotation S1. In some embodiments, the shift S4 is to gradually reduce the gap width w until the determined occurrence rate of S3 exceeds a predetermined occurrence rate threshold T, defining a minimum value m of the gap width. In some embodiments, the method may then include monitoring, S5, the change of the minimum value over time, which indicates progressive wear of the first disc and / or the second disc 2. In some other embodiments, the shift S4 is used to adjust the gap width w so that the occurrence rate of the determined S3 is kept within a predetermined occurrence rate range R.

[0031] Figure 5 The vibration spectrum 50 is illustrated. The spectrum can represent vibration amplitudes (energy) at different frequencies, i.e., in the frequency domain rather than the time domain, for example, at any given time or time interval, the frequency f is on the X-axis and the vibration amplitude A is on the Y-axis, as shown. The spectrum includes or consists of mechanical vibrations within the grinding apparatus 10 (e.g., its housing 21), caused by the rotation S1 of the first disc 2a relative to the second disc 2b. For example, the mechanical vibrations can be measured over time (during a predetermined time interval), for example, by obtaining the sensor signal 23 of S2 from the vibration sensor 22. Frequency analysis can then be performed on the measured vibration data to obtain the spectrum 50. As described herein, the mechanical vibrations depend on the gap width, but also on, for example, the rotational speed of the rotor 3a, the number of teeth in the grinding discs 2a and 2b, and the construction and / or wear of said teeth.

[0032] From the spectrum 50, vibration peaks 54 at various frequencies can be determined, wherein if the vibration amplitude A at a particular frequency exceeds a predetermined threshold 51, then the particular frequency at the vibration peak is defined as the particular frequency. The frequency resolution that separates vibrations of different frequencies from each other can be predetermined, for example, depending on the sampling frequency and sampling time (i.e., the number of samples).

[0033] When determining the occurrence rate of vibration peaks 54 in the S3 spectrum 50, vibration peaks within a predetermined frequency range 52 can be considered. The occurrence rate can be considered as the density of vibration peaks in the frequency domain of the spectrum, i.e., the number of peaks at various different frequencies within each predetermined frequency range of the spectrum. In some embodiments, the occurrence rate of vibration peaks 54 is defined by the number of vibration peaks within the frequency range 52. Additionally or alternatively, in some embodiments, the occurrence rate of vibration peaks 54 is defined by the average distance 53 between adjacent vibration peaks 54 within the frequency range 52. Because the average distance 53 between peaks 54 within the range 52 depends on the number of peaks 54 within the range 52, whether to consider the number of peaks 54 and / or the average distance 53 between the peaks 54 may simply be a matter of easier analysis.

[0034] Figure 6 The illustration shows an example of the occurrence rate of determining, for example, the number of vibration peaks 54 as a function of the gap width w, which is measured, for example, as the axial position of one of the grinding discs 2a and 2b, or as the axial position of the rotor 3a. Generally, the occurrence rate increases as the gap width w decreases. When the occurrence rate exceeds a predetermined occurrence rate threshold T, a minimum gap width m, known as zeroing, can be defined. Therefore, the minimum value m of the gap width w can be defined by axially shifting one grinding disc 2a towards the other grinding disc 2b by S4 until the occurrence rate of the determined S3 exceeds the predetermined occurrence rate threshold T.

[0035] In some embodiments, it may be necessary to maintain a relatively constant occurrence rate of vibration peak 54 during operation of the grinding apparatus 10, and this is typically achieved by adjusting the gap width w by axially shifting one of the discs in disc S4 as needed. Therefore, in some embodiments, one disc in disc S4 may be axially shifted to adjust the gap width w such that the determined occurrence rate of S3 is maintained within a predetermined occurrence rate range R. For example, in some embodiments, during operation of the grinding apparatus 10, the grinding disc 2a may be axially shifted from a defined minimum gap width w to an operating gap width defined by the occurrence rate of vibration peak 54 within the occurrence rate range R. The occurrence rate at the operating gap width may vary over time, for example, decreasing due to wear of the grinding discs; this is why axial shifting S4 during operation, for example, axially moving the rotor 3a toward the stator 3b, is performed to maintain the occurrence rate within the occurrence rate range R.

[0036] The present disclosure has been described above primarily with reference to several embodiments. However, as will be readily understood by those skilled in the art, other embodiments besides those disclosed above may also be within the scope of the present disclosure as defined by the appended claims.

Claims

1. A method for monitoring the width (w) of a gap (1) between two grinding discs (2) in a grinding apparatus (10) for processing a fiber fluid (6), executed by a controller (20), the method comprising: The first disk (2a) of the grinding disk is rotated about the rotation axis (5) of the first disk relative to the second disk (2b) of the grinding disk. Obtain the spectrum (50) of the mechanical vibration in the grinding apparatus (10) caused by the rotation of the first disk (2a) relative to the second disk (2b); Within a predetermined frequency range (52) of the obtained spectrum (50), the occurrence rate of vibration peaks (54) is determined, the occurrence rate being the density of vibration peaks in the frequency domain of the spectrum, and the occurrence rate being an indication of the gap width (w).

2. The method according to claim 1, wherein each vibration peak in the vibration peak (54) in the spectrum (50) is defined as a vibration peak at the specific frequency (f) of the peak by exceeding a predetermined vibration amplitude (A) threshold (51) at a specific frequency of the peak.

3. The method according to any one of the preceding claims, wherein the occurrence rate of the vibration peak (54) is defined by the number of vibration peaks within the frequency range (52), or by the average distance (53) between adjacent vibration peaks within the frequency range.

4. The method according to any one of claims 1 to 2, further comprising: During the rotation, at least one of the first disk and the second disk is shifted along the rotation axis (5) to: Gradually decrease the gap width (w) until the determined occurrence rate exceeds a predetermined occurrence rate threshold (T), and define a minimum value (m) for the gap width; or The gap width (w) is adjusted so that the determined occurrence rate is kept within a predetermined occurrence rate range (R).

5. The method according to claim 4, further comprising: The minimum value is monitored to change over time, and the change indicates the progressive wear of the first disk (2a) and / or the second disk (2b).

6. The method according to any one of claims 1 to 2, wherein the spectrum (50) is obtained by means of a vibration sensor (22), the vibration sensor including, for example, an accelerometer.

7. The method according to claim 6, wherein the vibration sensor (22) is arranged to measure the vibration of the housing (21) of the grinding equipment (10).

8. The method according to any one of claims 1 to 2, wherein the spectrum (50) is obtained when the fiber fluid is passed through the gap (1).

9. The method of claim 8, wherein the fiber fluid is a slurry.

10. The method of claim 8, wherein the fiber fluid is a bio-plasma.

11. The method according to any one of claims 9 to 10, wherein the fibers in the fiber fluid comprise cellulose.

12. The method according to any one of claims 9 to 10, wherein the fibers in the fiber fluid are composed of cellulose.

13. A controller (20), comprising: Processing circuit (31); as well as The storage device (32) stores instructions (33) that can be executed by the processing circuit (31), thereby enabling the controller (20) to operate in a grinding apparatus (10) comprising two grinding discs (2) to perform the method according to any one of the preceding claims.

14. A grinding apparatus (10), comprising: The controller (20) according to claim 13; as well as First grinding disc and second grinding disc.

15. The grinding equipment according to claim 14, wherein the grinding equipment (10) is a disperser, a fine grinder or a dispersing machine.

16. A computer program product (32) comprising a computer executable component (33) for causing the controller (20) to perform the method according to any one of claims 1 to 12 when the computer executable component (33) is running on a processing circuit (31) included in a controller of a grinding apparatus (10) comprising two grinding discs (2).

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