Wireless monitoring-based coarse control method for vibrating screen of coal washing plant

Abstract

The present application relates to the field of vibration screen run coarse control, and particularly relates to a coal washing plant vibration screen run coarse control method based on wireless monitoring. According to the vibration signals, impact signals and current signals collected in real time after the vibration screen is started, a dynamic reference interval is constructed to replace the fixed threshold as the determination reference, the false alarm and the missed alarm caused by the fluctuation of the feeding working condition are avoided, and the accuracy of the run coarse determination is ensured. According to the change direction and the change rate of the vibration deviation and the impact deviation, pre-selection is performed, the deviation types are divided into pulse type, drift type or continuous type, so that the abnormality of the vibration screen is captured before the run coarse occurs, and passive alarm after the run coarse occurs is avoided, and time for early intervention is obtained.

Description

Technical Field

[0001] This invention relates to the field of coarse screen control, specifically to a method for controlling coarse screen coarseness in coal washing plants based on wireless monitoring. Background Technology

[0002] Vibrating screens are screening and grading equipment in coal washing plants. They use a vibrator to drive the screen box to reciprocate, separating the mixed materials according to particle size. However, vibrating screens operate in harsh environments with high dust, strong vibration, and high humidity for extended periods. It is difficult to completely avoid screen wear, local damage, or screen plate detachment, which leads to coarse material being passed through the screen, thus deteriorating the quality of the clean coal product. In severe cases, it can even cause the entire production line to shut down.

[0003] In response, existing technologies include using industrial cameras to capture images of slurry screens, identifying coal particle areas from these images, calculating the proportion of coarse particles in these areas, comparing it with a preset threshold, determining whether coarse particles have escaped, and issuing an alarm.

[0004] However, the existing technology still has the following two drawbacks: First, using a preset threshold as the basis for judging coarseness, when the feed is coarse and the screen is not damaged, the fixed preset threshold is prone to false alarms; when the feed is fine and the screen has been slightly damaged, the proportion of coarse particles in the large amount of fine material is insufficient, resulting in missed alarms; and when the alarm is triggered, the coarseness accident has already occurred, and the large particles have already caused irreversible damage to the subsequent equipment and product quality, making it impossible to capture and control the abnormality of the vibrating screen's operating status before coarseness occurs.

[0005] Secondly, the visual inspection method that uses industrial cameras to capture images of the slurry screen plate can only capture the appearance features of the material on the screen and cannot reflect the real-time changes in the operating status of the vibrating screen. When the camera's field of view is limited, the lens is contaminated by the slurry, or the lighting conditions change, the reliability of the inspection drops significantly. Furthermore, the deployment of wired cameras is limited by the length and direction of the cable, and long-distance cables are prone to breakage due to vibration fatigue, which further reduces the reliability. Summary of the Invention

[0006] The technical solution adopted by this invention to solve its technical problem is: a method for controlling coarseness of a vibrating screen in a coal washing plant based on wireless monitoring, which includes: after the vibrating screen is started, statistically analyzing the amplitude distribution of three equipment-end signals, including vibration signal, impact signal and current signal, within the sampling window, and constructing a dynamic reference interval corresponding to the current feeding condition.

[0007] Based on the dynamic reference interval, the vibration deviation, impact deviation and current deviation corresponding to the three device end signals are calculated in real time.

[0008] Based on the changing direction of vibration deviation and impact deviation, pre-screening is performed to determine the deviation type; the deviation types include pulse type, drift type and continuous type.

[0009] When the deviation type is pulse type, the system determines whether to trigger an anomaly warning based on the cumulative number of pulse type deviations; when the deviation type is drift type, the system determines whether to trigger a drift warning based on the corresponding deviation amplitude.

[0010] When the deviation type is continuous, the initial roughness level is determined based on the deviation ratios of vibration deviation, impact deviation, and current deviation.

[0011] The initial coarsening grade is corrected based on the upstream feed rate and the particle size distribution of the incoming material to obtain the final coarsening grade; a graded control command is output based on the final coarsening grade.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The present invention constructs a dynamic reference interval based on the vibration signal, impact signal and current signal collected in real time after the vibrating screen is started, so as to replace the fixed threshold as the judgment benchmark, avoid false alarms and missed alarms caused by fluctuations in the feeding conditions, and ensure the accuracy of coarseness judgment; according to the direction and rate of change of vibration deviation and impact deviation, pre-screening is performed to classify the deviation type into pulse type, drift type or continuous type, so as to capture the abnormality of the vibrating screen before coarseness occurs, avoid passive alarm only after coarseness occurs, and gain time for early intervention.

[0013] 2. This invention collects vibration signals, impact signals, and current signals by deploying vibration acceleration sensors on the side plates of the screen box, tuning fork-type contact sensors on the inner wall of the under-screen collection hopper, and current transformers in the power supply lines of the drive motor. After analog-to-digital conversion, these signals are transmitted to the central control center via their respective wireless transmission modules. This wireless transmission method replaces wired deployment, avoiding the breakage of long-distance cables due to vibration fatigue. At the same time, physical sensors replace industrial cameras, which are unaffected by dust and lighting conditions, ensuring the reliable operation of the monitoring system in harsh environments. Attached Figure Description

[0014] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 This is a schematic diagram of the method flow of the present invention;

[0016] Figure 2 A schematic diagram illustrating the process of constructing a dynamic reference interval for this invention;

[0017] Figure 3 This is a schematic diagram of the pre-screening process of the present invention;

[0018] Figure 4 This is a schematic diagram of the process for determining the initial coarseness grade in this invention. Detailed Implementation

[0019] Various exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It should be noted that, unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of the invention. Furthermore, it should be understood that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale.

[0020] The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the invention or its application or use. Techniques, methods, and apparatus known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and apparatus should be considered part of the specification.

[0021] In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values.

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0023] The specific scheme of the method for controlling coarseness control of a vibrating screen in a coal washing plant based on wireless monitoring, provided by the present invention, is described in detail below with reference to the accompanying drawings.

[0024] Please see Figure 1 and Figure 2 As shown, the present invention provides a method for controlling the coarseness of a vibrating screen in a coal washing plant based on wireless monitoring, including: step S1, after the vibrating screen is started, statistically analyze the amplitude distribution of three equipment-end signals, including vibration signal, impact signal and current signal, within the sampling window, and construct a dynamic reference interval corresponding to the current feeding condition.

[0025] In this embodiment, vibration signals are collected using a vibration acceleration sensor installed on the side plate of the screen box; impact signals are collected using a tuning fork-type contact sensor installed on the inner wall of the under-screen hopper; and current signals are collected using a current transformer installed in the power supply line of the drive motor. Each sensor converts the collected signals from analog to digital and then transmits them to the central control center via its respective wireless transmission module.

[0026] After the vibrating screen is started, it first goes through a 5 to 15 second no-load operation phase. After the upstream feeder starts and the material enters the screen surface, the sliding window analysis begins.

[0027] Specifically, taking the current sampling time as the endpoint, a sliding window is formed by going back a certain time. The standard deviation of the vibration signal amplitude (i.e., the instantaneous amplitude of vibration acceleration) at all sampling times within the sliding window is calculated and denoted as the vibration acceleration standard deviation.

[0028] Next, the standard deviation of vibration acceleration in the subsequent sliding window is subtracted from the standard deviation of vibration acceleration in the preceding adjacent sliding window. The absolute value of this difference is then divided by the standard deviation of vibration acceleration in the preceding adjacent sliding window to obtain the relative rate of change of the vibration acceleration standard deviation. To avoid misjudgment, when 10 consecutive relative rates of change are all below the allowable limit, the feeding condition is determined to be in steady-state operation, the sampling window is opened, and the first sampling time of the sliding window corresponding to the first relative rate of change among the aforementioned 10 consecutive relative rates of change is taken as the starting time of the sampling window; otherwise, the feeding condition is not determined to be in steady-state operation, the sampling window is not opened, and the sliding window analysis continues.

[0029] Based on industrial control practices, the allowable limit is set at 5%; to ensure statistical representativeness, the length of the sliding window is set at 0.5s; considering that the material residence period of the vibrating screen is usually 15 to 30s, to ensure that the sampling window fully covers at least one material residence period, thereby collecting data that fully reflects the steady-state operating characteristics of the entire screen surface, the length of the sampling window is set at 30s.

[0030] If the sampling window is not opened after the maximum waiting time since the start of the sliding window analysis, a timeout alarm will be triggered, prompting staff to check for malfunctions in the vibrating screen and abnormal feeding upstream. At the same time, the sampling window will be forcibly opened with the end of the maximum waiting time as the start time. To avoid false alarms and ensure the timeliness of the timeout alarm, the maximum waiting time is set to 3 times the material residence time.

[0031] The material residence time was determined through on-site tracer experiments. Specifically, markers were placed at marked points on the vibrating screen surface and the time it took for the markers to reach another marked point on the screen surface was measured. The distance between the two marked points on the screen surface was measured, and the measured distance was divided by the measured time to obtain the material travel speed. Then, the screen surface length obtained from the technical documents of the vibrating screen was divided by the material travel speed to obtain the material residence time.

[0032] Within the sampling window, the amplitudes of the vibration signal, impact signal, and current signal are arranged in ascending order to obtain three amplitude sequences.

[0033] Taking a vibration signal as an example, its corresponding amplitude sequence is the acceleration sequence. The median of the acceleration sequence is extracted, and the difference between each vibration acceleration in the sequence and the median is calculated. The absolute value of the difference is divided by the absolute value of the median. When the result is greater than a preset proportion, the corresponding vibration acceleration is removed from the acceleration sequence, resulting in the retained segment of the vibration signal. To exclude instantaneous impacts while retaining periodic fluctuations, the preset proportion is set to 20%.

[0034] Next, the arithmetic mean and standard deviation of the vibration acceleration in the retained segments are calculated and used as the amplitude mean and amplitude standard deviation, respectively. Based on the statistical 3σ principle, the amplitude mean is increased by three times the amplitude standard deviation to obtain the upper limit of the vibration signal amplitude; the amplitude mean is decreased by three times the amplitude standard deviation to obtain the lower limit of the vibration signal amplitude; the upper limit of the amplitude is used as the upper limit of the dynamic reference interval, and the lower limit of the amplitude is used as the lower limit of the dynamic reference interval, thus obtaining the dynamic reference interval corresponding to the vibration signal.

[0035] It should be noted that if the number of vibration accelerations in the retained segment is less than two, the data in this sampling window is considered abnormal, the construction of the dynamic reference interval is abandoned, the sliding window analysis continues, and the system waits for the sampling window to open again. If, after the maximum waiting time has elapsed since the start of the sliding window analysis, the dynamic reference interval cannot be constructed due to insufficient vibration acceleration data in the retained segment, a sampling abnormality alarm will be pushed out, prompting staff to check the sensor status and the operating condition of the vibrating screen.

[0036] Similarly, by obtaining the upper and lower limits of the current signal amplitude in the same way, the dynamic reference range corresponding to the current signal can be obtained.

[0037] For impact signals, since their signal characteristics are event-driven and their amplitude distribution exhibits non-normal and skewed features, a quantile method is used to construct a dynamic reference interval. Specifically, the 1st percentile in the corresponding amplitude sequence is taken as the lower limit of the amplitude, and the 99.7th percentile is taken as the upper limit of the amplitude. The 1st percentile is used to distinguish between no-impact and impact states; the 99.7th percentile is used to distinguish between normal impacts and abnormal impacts.

[0038] The dynamic reference interval characterizes the permissible statistical fluctuation range of signals from each equipment terminal during steady-state operation under the current feeding conditions.

[0039] Step S2: Based on the dynamic reference interval, calculate in real time the vibration deviation, impact deviation and current deviation corresponding to the three device end signals.

[0040] For vibration signals, the control center acquires the vibration acceleration at each sampling time. If the vibration acceleration is greater than or equal to the lower limit of the corresponding dynamic reference interval and less than or equal to the upper limit, it indicates that the screen box vibration is within the allowable statistical fluctuation range, and the vibration deviation is recorded as zero. If the vibration acceleration is greater than the upper limit of the corresponding dynamic reference interval, it indicates that the screen box vibration is abnormally enhanced and not within the allowable statistical fluctuation range; the difference between the vibration acceleration and the upper limit is taken as the vibration deviation, which is positive. If the vibration acceleration is less than the lower limit of the corresponding dynamic reference interval, it indicates that the screen box vibration is abnormally weakened and not within the allowable statistical fluctuation range; the difference between the vibration acceleration and the lower limit is taken as the vibration deviation, which is negative. Similarly, the current deviation is obtained in the same way.

[0041] Considering that when no material particles collide with the inner wall of the under-screen hopper, i.e., no impact event occurs, the impact signal only reflects the background fluctuations of the operating conditions and cannot be used as a basis for analyzing and quantifying the impact deviation, the impact deviation is calculated on a per-impact-event basis.

[0042] Specifically, the control center acquires the impact signal amplitude, i.e., the impact voltage, at each sampling time. To prevent false triggering caused by sensor background noise or transient electromagnetic interference, an impact event is determined to have started when the impact voltage is greater than the corresponding lower limit within a preset trigger duration. Otherwise, the impact event is not determined to have started, and subsequent impact voltages are evaluated. When an impact event is determined to have started, the impact voltage is first greater than the lower limit within the preset trigger duration, indicating that a physical impact has actually occurred. Therefore, the first sampling time within the preset trigger duration is taken as the start time of the impact event.

[0043] From the start of the impact event, to avoid interference from signal jitter during the impact attenuation process, the impact event is considered to have ended when the impact voltage drops below the lower limit within a preset confirmation period; otherwise, the impact event is not considered to have ended, and the impact voltage is continued to be judged. When the impact voltage is lower than the lower limit for the first time within the preset confirmation period, it indicates that the impact energy has dissipated and the physical impact process has essentially ended. Therefore, the first sampling time within the preset confirmation period is taken as the end time of the impact event.

[0044] To filter out background noise and transient electromagnetic interference, the preset trigger duration is set to 3 times the sampling period; to fully cover the decay time of the tuning fork touch sensor, the preset confirmation duration is set to 5 times the sampling period. The sampling period is a unified time interval for the central control center to synchronously sample the vibration acceleration sensor, tuning fork touch sensor, and current transformer, and it is read from the control parameters of the central control center.

[0045] Then, the maximum value of the impact voltage between the start and end times of the impact event is extracted as the peak amplitude of the impact signal. If the peak amplitude is greater than the upper limit of the corresponding dynamic reference interval, the difference between the peak amplitude and the upper limit is taken as the impact deviation, and the impact deviation is positive. If the peak amplitude is less than or equal to the upper limit of the corresponding dynamic reference interval, the impact deviation is zero.

[0046] It should be noted that between two consecutive impact events, that is, during the time period from the end of the previous impact event to the beginning of the next impact event, the impact deviation remains the same as that of the previous impact event, thus assigning a specific impact deviation to each sampling time.

[0047] Step S3: Based on the changing direction of vibration deviation and impact deviation, perform pre-screening to determine the deviation type; the deviation types include pulse type, drift type and continuous type.

[0048] Autocorrelation analysis was performed on the vibration acceleration sequence within the sampling window in step S1. Based on the half-power point principle in signal processing, the delay time at which the autocorrelation function value first decays to 0.5 was taken as the response time. The above autocorrelation analysis and autocorrelation function calculation processes all utilize existing techniques and will not be elaborated upon here.

[0049] Then, the signs of the vibration deviation and impact deviation are used as the direction of change; if the vibration deviation or impact deviation is zero, there is no corresponding direction of change and it is not used to determine whether the subsequent direction of change has changed.

[0050] In addition, since anomalies at the feed end of the screen require a material residence time before being transmitted to the tuning fork-type contact sensor on the under-screen hopper, twice the material residence time is used as the fixed duration of the observation window to ensure that the observation window fully covers the entire process from the occurrence to the end of the anomaly. The observation window is then captured backward from the current sampling time.

[0051] Please see Figure 3 As shown, in order to classify abnormal situations that deviate from the normal operating state of the vibrating screen in detail, thereby achieving graded response and avoiding false alarms, missed alarms and inappropriate responses, pre-screening is required to determine the type of deviation.

[0052] First, event recognition is performed after the observation window ends. For ease of description, vibration deviation and impact deviation are collectively referred to as deviation.

[0053] The event recognition process is as follows: if all corresponding deviations within the observation window are zero, they are recorded as zero values ​​throughout; if all corresponding deviations within the observation window are not zero, they are recorded as non-zero values ​​throughout.

[0054] If the deviation value in the observation window changes from zero to a non-zero value, a deviation event is determined to have occurred. The sampling time when the deviation value changes from zero to a non-zero value is taken as the start time of the deviation event, and the sampling time when the deviation value returns to zero from a non-zero value is taken as the end time of the deviation event. The corresponding deviation event is recorded as a complete end event.

[0055] If the deviation value in the current observation window changes from zero to a non-zero value, but the corresponding deviation value does not fall back to zero afterward, the deviation event is determined to be unfinished. The corresponding deviation event is recorded as an unfinished event, and the sampling time when the corresponding deviation value becomes zero is tracked in subsequent observation windows. That is, a cross-window tracking operation is performed, and the deviation value corresponding to the cross-window tracking operation is recorded as the tracked deviation value.

[0056] The specific process of cross-window tracking is as follows: If the tracked deviation amount within the current observation window falls back to zero from a non-zero value, the sampling time when it falls back to zero is recorded as the end time of the corresponding deviation event. The time difference between the start and end times of the deviation event is calculated as the duration, and the current cross-window tracking process is terminated. The corresponding deviation event is recorded as a complete end event. If the tracked deviation amount falls back to zero from a non-zero value and then reappears as a non-zero value, it is considered a new deviation event. The sampling time when the non-zero value reappears is recorded as the start time of the new deviation event.

[0057] If the tracked deviation is continuously non-zero within the current observation window, the time difference between the sampling time when the tracked deviation first becomes non-zero and the end point of the current observation window is calculated as the first cumulative duration. When the first cumulative duration is greater than or equal to the fixed duration of the observation window, the current cross-window tracking process is forcibly terminated, and the corresponding deviation event is recorded as a timeout termination event. If the first cumulative duration is less than the fixed duration of the observation window, the corresponding deviation event is recorded as an unfinished event, and the cross-window tracking process of the tracked deviation continues.

[0058] Subsequently, window boundary backtracking verification is performed on deviations that are determined to be non-zero throughout the entire process. The backtracking verification process is as follows: with the current sampling time as the endpoint, backtracking is performed for a fixed duration of one observation window to confirm whether the deviation has experienced returning to zero. If the deviation has experienced returning to zero, the zeroing time with the smallest time difference from the current sampling time is taken as the most recent zeroing time. The time difference between the sampling time when the first non-zero value appears after the most recent zeroing time and the endpoint of the current observation window is calculated as the second cumulative duration.

[0059] If the deviation has not reached zero, the start time of the observation window is taken as the start time of this deviation event, i.e., the sampling time when the first non-zero value appears, and the second cumulative duration is taken as the fixed duration of the observation window. When backtracking is not possible due to reasons such as communication interruption recovery or sensor power-on, the same processing method is used for cases where the deviation has not reached zero.

[0060] After the backtracking verification is completed, the following judgment is made based on the second cumulative duration: if the second cumulative duration is greater than or equal to the fixed duration of the observation window, the corresponding deviation event is recorded as a timeout termination event; if the second cumulative duration is less than the fixed duration of the observation window, the corresponding deviation event is recorded as an unfinished event.

[0061] Then, based on whether there are any unfinished events after the current observation window ends, perform classification processing.

[0062] The classification process is as follows: If there are unfinished events after the current observation window ends, the deviation type is not determined for the time being. The deviation amount, start time of the deviation event, first cumulative duration, second cumulative duration and change direction of all unfinished events are passed to the next observation window as input for the cross-window tracking preprocessing in the next observation window.

[0063] If there are no unfinished events after the current observation window ends, the maximum value among the duration of all complete ending events and timeout termination events, the first cumulative duration, or the second cumulative duration is extracted as the baseline duration, and the corresponding deviation is used as the baseline deviation. If multiple maximum values ​​appear among the duration of all complete ending events and timeout termination events, the deviation at the earliest sampling time of the first non-zero value among the maximum values ​​is taken as the baseline deviation. If the sampling time of the first non-zero value is also the same, the impact deviation is taken as the baseline deviation.

[0064] Finally, the deviation type is determined: if both the vibration deviation and impact deviation are zero throughout, it is determined that no deviation event has occurred. Otherwise, a judgment is made based on the event type corresponding to the baseline deviation.

[0065] The process of determining the type of event corresponding to the baseline deviation is as follows: when the deviation event corresponding to the baseline deviation is a complete termination event, if the baseline duration is less than or equal to the response time, the deviation type is determined to be pulse type; if the baseline duration is greater than the response time, the deviation type is determined to be drift type.

[0066] When the deviation event corresponding to the reference deviation is a timeout termination event, if the direction of change does not change during the duration of the reference, the deviation type is determined to be continuous; if the direction changes during the duration of the reference, the deviation type is determined to be pulsed.

[0067] Step S4: When the deviation type is pulse type, determine whether to trigger an abnormality warning based on the cumulative number of pulse type deviations; when the deviation type is drift type, determine whether to trigger a drift warning based on the corresponding deviation amplitude.

[0068] First, the central control center counts the number of times that are identified as pulses within the sampling window, which is recorded as the reference pulse count. The reference pulse count represents the pulse frequency during steady-state operation under the current feeding conditions.

[0069] When the deviation type output in step S3 is pulse type, the central control center continuously counts the cumulative number of times that are judged to be pulse type within a time period with the current sampling time as the end point and the duration as the sampling window length.

[0070] If the cumulative number of vibrations exceeds the reference pulse count, and the system is not currently in an anomaly warning activation state, an anomaly warning will be triggered and marked as active; otherwise, no anomaly warning will be triggered. Triggering an anomaly warning indicates that the vibration may be due to loose components or localized screen damage causing intermittent coarseness, requiring staff to be alerted.

[0071] When the anomaly warning is active, if the cumulative number of pulses drops to less than or equal to the reference pulse number, it is determined that the frequency of abnormal impacts has returned to normal, the anomaly warning is lifted, and the anomaly warning activation mark is cleared; otherwise, the anomaly warning is not lifted, and the anomaly warning activation mark is maintained, thereby avoiding repeated triggering of the anomaly warning by the same anomaly.

[0072] When the deviation type is determined to be drift type, the absolute values ​​of all non-zero values ​​within the duration of the first deviation event in the observation window are extracted, and the maximum value among them is taken as the deviation amplitude. The deviation amplitude reflects the maximum degree of deviation from its dynamic reference range during this drift process.

[0073] If the deviation amplitude is greater than the difference between the upper and lower limits of the corresponding dynamic reference interval, and the current state is not in a drift warning activation state, a drift warning will be triggered and the screen will be marked as having a drift warning activation state; otherwise, a drift warning will not be triggered. Triggering a drift warning indicates that the condition of the vibrating screen is deteriorating and early intervention is required.

[0074] In the state of drift warning activation, in order to avoid the erroneous cancellation of drift warning due to momentary jitter, when the continuous duration of the corresponding deviation amount that triggers the drift warning returning to zero is greater than or equal to the preset confirmation duration in step S2, it is determined that the deviation has been eliminated, the drift warning is cancelled and the drift warning activation mark is cleared at the same time; otherwise, the drift warning is not cancelled and the drift warning activation mark is maintained.

[0075] Step S5: When the deviation type is continuous, determine the initial roughing level based on the deviation ratio of vibration deviation, impact deviation, and current deviation.

[0076] Please see Figure 4As shown, firstly, the absolute values ​​of vibration deviation, impact deviation, and current deviation at the last few sampling moments in the observation window are extracted respectively, and their average values ​​are calculated to obtain the mean values ​​of vibration deviation, impact deviation, and current deviation. Specifically, the last few sampling moments are taken from the last 20% of the sampling moments in the observation window to reflect the latest status and avoid misjudgment due to single-point interference.

[0077] Next, the vibration deviation from the mean is divided by the difference between the upper and lower limits of the dynamic reference interval corresponding to the vibration signal to obtain the deviation ratio of the vibration deviation, which is denoted as the vibration deviation ratio; similarly, the impact deviation ratio and the current deviation ratio are obtained.

[0078] Next, the process position type of the vibrating screen is obtained from the equipment parameter configuration in the central control center. The process position types include grading screen, desliming screen, and product screen. Among them, for the grading screen, the vibration signal responds more promptly to fluctuations in the feed, so the vibration deviation weight is set to 0.6 and the current deviation weight is set to 0.4; for the desliming screen, the current signal responds more promptly to load changes caused by media adhesion, so the vibration deviation weight is set to 0.4 and the current deviation weight is set to 0.6; for the product screen, the vibration signal and the current signal need to be considered in a balanced way, so the vibration deviation weight is set to 0.5 and the current deviation weight is set to 0.5.

[0079] Next, the vibration deviation ratio is multiplied by the vibration deviation weight, and the current deviation ratio is multiplied by the current deviation weight. The sum of the products yields the comprehensive deviation index. The comprehensive deviation index comprehensively reflects the overall degree of deviation between the operating state of the vibrating screen and the driving load.

[0080] Impact signals directly reflect the impact of large particles on the undersize hopper and are direct evidence of coarse material run-off. In order to avoid diluting its abnormal characteristics by vibration and current signals and to ensure the response speed of coarse material run-off judgment, the impact deviation ratio is not included in the calculation of the comprehensive deviation index.

[0081] Next, a classification judgment is made based on the comprehensive deviation index and the impact deviation ratio. Specifically, if any of the following conditions are met, the preliminary roughness level is determined to be level three: 1) the impact deviation ratio is greater than 3; 2) the comprehensive deviation index is greater than 5.

[0082] If neither condition 1) nor condition 2) is met, the initial roughness level is determined to be level 2 if the impact deviation ratio is greater than 2 or the comprehensive deviation index is greater than 3; otherwise, the initial roughness level is determined to be level 1.

[0083] Among them, conditions 1) and 2) are based on the action limit settings in the field of statistical process control; condition 1) indicates that the impact deviation is greater than 3 times the difference between the corresponding upper and lower limits, indicating strong large particle impact, the deviation of the impact signal is not caused by random fluctuations, and the confidence of screen breakage is high; condition 2) indicates that the overall deviation of the vibration signal and the current signal is greater than 5 times the difference between the corresponding upper and lower limits, and the vibrating screen is not caused by random fluctuations relative to steady-state operation.

[0084] In addition, an impact deviation ratio greater than 2 indicates that the average impact deviation is more than twice the difference between the upper and lower limits of the corresponding value, and there is a high possibility of large particle impact; a comprehensive deviation index greater than 3 indicates that the overall deviation between the vibration signal and the current signal is relatively large.

[0085] Step S6: Based on the upstream feed rate and incoming particle size distribution, correct the initial coarsening grade to obtain the final coarsening grade; based on the final coarsening grade, output the grading control command.

[0086] First, the central control center reads the feed rate of the upstream feeder from the weighing sensor within the corresponding time period of the observation window that is determined to be continuous, and calculates the arithmetic mean of the read feed rate as the current average feed rate; at the same time, the central control center reads the upper and lower limits of the rated feed rate from the equipment nameplate of the upstream feeder.

[0087] When the current average feed rate is greater than the upper limit of the rated feed rate, it is easy to cause the screen material layer to be too thick, and fine particles will be discharged before passing through the screen, resulting in overload and coarse material run-off. When the current average feed rate is less than the lower limit of the rated feed rate, it will not directly cause coarse material run-off, but it indicates that there may be blockage or flow interruption in the upstream feeding system.

[0088] Therefore, if the current average feed rate is greater than the upper limit of the rated feed rate or less than the lower limit of the rated feed rate, the feed rate is determined to be abnormal; otherwise, the feed rate is determined to be normal.

[0089] Meanwhile, the control center obtains the upper limit of the feed particle size from the process design documents of the vibrating screen, and obtains the particle size distribution data of the upstream incoming material from the online particle size analyzer installed on the upstream transfer belt. From the particle size distribution data, the percentage of the volume of particles larger than the upper limit of the feed particle size in the upstream incoming material at each sampling time is extracted and recorded as the over-limit percentage.

[0090] Arrange the excess percentages corresponding to each sampling time in the sampling window included in step S1 in chronological order of sampling time to obtain the excess percentage sequence; calculate the arithmetic mean and standard deviation of the excess percentage sequence, and denot them as the average percentage and the standard deviation of the percentage, respectively; based on the experience design in the field of statistical process control, add the average percentage to three times the standard deviation of the percentage to obtain the excess ratio.

[0091] The system monitors the percentage of samples exceeding the limit at each sampling time after the sampling window in real time. When the percentage of samples exceeding the limit is greater than the proportion of samples exceeding the limit, it indicates that the incoming material particle size is too large, which leads to accelerated screen wear. In this case, the incoming material particle size is determined to be abnormal. When the percentage of samples exceeding the limit is less than or equal to the proportion of samples exceeding the limit, the incoming material particle size is determined to be normal.

[0092] Subsequently, based on the above judgment results, the initial coarsening level is revised. Specifically: if there is an abnormality in the feed rate or the particle size of the incoming material when the initial coarsening level is level two or three, it indicates that the cause of the coarsening may be upstream rather than a problem with the vibrating screen itself. Therefore, the initial coarsening level is lowered by one level as the final coarsening level, and an upstream incoming material abnormality alarm is pushed to prompt priority investigation of upstream problems. If there is no abnormality in the feed rate or the particle size of the incoming material, it indicates that the cause of the coarsening is a problem with the vibrating screen itself. Therefore, the initial coarsening level is directly used as the final coarsening level, and a screen breakage warning is pushed.

[0093] When the initial coarsening grade is Level 1, since the deviation is relatively minor, the final coarsening grade will be set to Level 1 regardless of whether there are abnormalities in the feed rate or the particle size of the incoming material.

[0094] Next, based on the corrected final coarsening level, the central control center outputs the corresponding grading control command. Specifically, when the final coarsening level is level one, the first control command is output to adjust the inverter output frequency and the vibrator excitation force to change the material's movement speed and stratification effect on the screen surface, thus restoring the screening process to normal.

[0095] The process for determining the adjustment direction of the inverter output frequency and the excitation force of the vibrator is as follows: If the impact deviation is positive, it indicates that the screen material layer is too thick or the material is moving too slowly. The adjustment direction is determined to be positive, and the excitation frequency and excitation force need to be increased to speed up the material movement. If the impact deviation is negative, the adjustment direction is determined to be negative, and the excitation frequency and excitation force need to be reduced.

[0096] The calculation process for the single-time adjustment amplitude of the inverter output frequency and the vibrator excitation force is the same. Taking the calculation of the single-time adjustment amplitude of the inverter output frequency as an example: calculate the absolute value of the difference between the inverter output frequency and the upper limit of the adjustable range of the inverter output frequency, as a reference difference; combine the reference difference and the specifications of the vibrating screen to determine the single-time adjustment amplitude. Specifically, for large vibrating screens with a screen length greater than or equal to 4.8m, due to their large inertia and slow response, 5% of the reference difference is taken as the single-time adjustment amplitude to prevent overshoot caused by an excessively large single-time adjustment amplitude; for medium and small vibrating screens with a screen length less than 4.8m, due to their small inertia and fast response, 10% of the reference difference is taken as the single-time adjustment amplitude to ensure timely adjustment. The upper limit of the adjustable range is obtained from the technical documents of the inverter or vibrator.

[0097] After adjusting the inverter output frequency and exciter excitation force, the central control center continuously monitors the impact deviation. If the impact deviation falls back to the dynamic reference range within one observation window, the first-level control is deemed effective, and the currently adjusted parameters are maintained. If the impact deviation does not fall back to the dynamic reference range within one observation window, the currently adjusted parameters are used as a benchmark, and adjustments are made in the adjustment direction with single-stage adjustment amplitudes. If the first-level control is still not deemed effective after three consecutive adjustments, adjustments are made in the opposite direction of adjustment with single-stage adjustment amplitudes, i.e., reverse adjustment is performed to avoid unidirectional over-adjustment leading to deterioration of the operating conditions.

[0098] If, after reverse backoff adjustment, the impact deviation falls back to the dynamic reference range within one observation window, the reverse backoff adjustment is deemed effective, and the parameters after this backoff are maintained. If, after reverse backoff, the impact deviation does not fall back to the dynamic reference range within one observation window, the parameters after this backoff are used as the benchmark, and reverse backoff adjustment continues.

[0099] If the reverse back adjustment is still not effective after three consecutive reverse back adjustments, it indicates that the current impact deviation is not caused by the frequency or excitation force deviation of the inverter. At this time, the frequency and excitation force of the inverter are restored to the values ​​before the first control command is output, and the final coarseness level is upgraded to level two. The second control command is executed, and at the same time, a level one control invalid alarm is pushed to prompt the staff to check whether there is a mechanical fault in the vibrating screen.

[0100] When the final coarsening stage reaches level two, a second control command is output to reduce the feeding speed of the upstream feeder. This reduces the feed rate and the thickness of the screen fabric, providing sufficient time and space for the fine-grained material to pass through the screen. The single speed reduction amplitude is set based on the same criteria as the single adjustment amplitude. Specifically, for large vibrating screens, the single speed reduction amplitude is 5% of the current feeding speed; for medium and small vibrating screens, the single speed reduction amplitude is 10% of the current feeding speed.

[0101] After reducing the feeding speed of the upstream feeder, the central control center continuously monitors the impact deviation. If the impact deviation decreases to the dynamic reference range within an observation window, the secondary control is deemed effective, and the current reduced feeding speed is maintained. If the impact deviation does not decrease to the dynamic reference range within an observation window, it indicates that reducing the speed alone is insufficient to solve the coarseness problem. The final coarseness level is upgraded to the third level, the third control command is executed immediately, and a screen breakage warning is pushed out.

[0102] When the final coarsening level is three, the third control command is output to drive the diversion flap valve at the discharge port to switch to the bypass position, thereby temporarily diverting the material on the vibrating screen to the bypass to prevent unqualified products from entering the subsequent process.

[0103] After the material is diverted, the central control center continuously monitors the impact deviation. When the impact deviation falls back to the dynamic reference range within an observation window and remains there for a preset confirmation period, a flap valve reset command is generated, driving the diversion flap valve to switch back to the main channel position. Otherwise, a diversion abnormality alarm is pushed and staff are prompted to check the diversion flap valve and bypass channel on-site. At the same time, the diversion flap valve is kept in the bypass position, and a screen breakage warning is continuously pushed until staff confirm on-site and manually reset it.

[0104] The above embodiments can be implemented, in whole or in part, by software, hardware, firmware, or any other combination thereof. When implemented using software, the above embodiments can be implemented, in whole or in part, in the form of a computer program product.

[0105] Those skilled in the art will recognize that the modules and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0106] In addition, the functional modules in the various embodiments of the present invention can be integrated into one processing module, or each module can exist physically separately, or two or more modules can be integrated into one module.

[0107] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

[0108] Finally, the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for controlling coarseness in a vibrating screen of a coal washing plant based on wireless monitoring, characterized in that, Includes the following steps: Step S1: After the vibrating screen is started, the amplitude distribution of the three equipment-end signals, including vibration signal, impact signal and current signal, is statistically analyzed within the sampling window to construct a dynamic reference interval corresponding to the current feeding condition; vibration signal, impact signal and current signal are collected respectively by the vibration acceleration sensor deployed on the side plate of the screen box, the tuning fork-type contact sensor on the inner wall of the under-screen collection hopper and the current transformer of the drive motor power supply line; The process of constructing a dynamic reference interval is as follows: After the vibrating screen is started, several sliding windows are defined with the current sampling time as the endpoint; Calculate the standard deviation of the vibration signal within the sliding window, and then calculate the relative rate of change of the standard deviation of the vibration signal within adjacent sliding windows. When multiple consecutive relative rates of change are all below the allowable limit, the sampling window is determined to be open. Within the sampling window, the amplitudes of the vibration signal, impact signal, and current signal are arranged in ascending order to obtain an amplitude sequence. For vibration and current signals, the median of the amplitude sequence is extracted, and the difference between each item in the amplitude sequence and the median is calculated. Amplitude items whose absolute difference exceeds a preset proportion of the absolute value of the median are removed to obtain the retained segments. Calculate the mean and standard deviation of the amplitude of the retained segments; Based on the mean amplitude and standard deviation of amplitude, determine the upper and lower limits of amplitude for each signal. For impact signals, the lower quantile of the corresponding amplitude sequence is taken as the lower limit of amplitude, and the higher quantile is taken as the upper limit of amplitude; The upper and lower limits of the amplitude are used as the upper and lower limits of the corresponding dynamic reference interval; Step S2: Based on the dynamic reference interval, calculate in real time the vibration deviation, impact deviation and current deviation corresponding to the three device end signals; The calculation process for vibration deviation and current deviation is as follows: For vibration signals, if the amplitude of the vibration signal is greater than the lower limit of the corresponding dynamic reference interval and less than the upper limit, then the vibration deviation is zero. If the vibration signal amplitude is greater than or equal to the upper limit of the corresponding dynamic reference interval, then the vibration deviation is the difference between the vibration signal amplitude and the upper limit. If the amplitude of the vibration signal is less than or equal to the lower limit of the corresponding dynamic reference interval, then the vibration deviation is the difference between the amplitude of the vibration signal and the lower limit. Similarly, the current deviation can be obtained by following the calculation process of vibration deviation. Step S3: Based on the changing direction of vibration deviation and impact deviation, perform pre-screening to determine the deviation type; Deviation types include pulse type, drift type, and persistent type; Step S4: When the deviation type is pulse type, determine whether to trigger an abnormality warning based on the cumulative number of times it is determined to be pulse type; When the deviation type is drift, determine whether to trigger a drift warning based on the corresponding deviation amplitude. Step S5: When the deviation type is continuous, determine the initial coarsening level based on the deviation ratio of vibration deviation, impact deviation, and current deviation. Step S6: Correct the initial coarsening grade according to the upstream feed rate and incoming particle size distribution to obtain the final coarsening grade; output the grading control command according to the final coarsening grade.

2. The method for controlling coarseness of a vibrating screen in a coal washing plant based on wireless monitoring as described in claim 1, characterized in that, The calculation process for impact deviation is as follows: For impact signals, when the amplitude of the impact signal is greater than the lower limit of the corresponding dynamic reference interval within the preset trigger duration, the impact event is determined to have started, and the first sampling time within the preset trigger duration is taken as the start time. From the start time, when the amplitude of the impact signal falls back to the lower limit of the corresponding dynamic reference interval within the preset confirmation time, the impact event is determined to be over, and the first sampling time within the preset confirmation time is taken as the end time. Extract the peak amplitude of the impact signal between the start and end times. If the peak amplitude is greater than the upper limit of the corresponding dynamic reference interval, the difference between the peak amplitude and the upper limit is taken as the impact deviation; otherwise, the impact deviation is zero. Between two consecutive impact events, the impact deviation remains the same as that between the two impact events.

3. The method for controlling coarseness control of a vibrating screen in a coal washing plant based on wireless monitoring as described in claim 2, characterized in that, The pre-screening process is as follows: The observation window is cut back to a fixed duration from the current sampling time; the fixed duration is determined based on the ratio of the screen surface length of the vibrating screen to the material travel speed. The vibration deviation and impact deviation are used as the deviation values, and the sign of the deviation values ​​is used as the direction of change; the response time is determined based on the vibration signal within the sampling window. When the deviation value in the observation window changes from zero to a non-zero value, a deviation event is determined to have occurred. The sampling moment when the deviation changes from zero to a non-zero value is taken as the start time of the deviation event, and the sampling moment when the deviation falls back to zero from a non-zero value is taken as the end time of the deviation event. If there are unfinished deviation events within the current observation window when the current observation window ends, the tracking will continue in subsequent observation windows until the deviation event ends or the termination condition is triggered. If there are no unfinished deviation events at the end of the current observation window, the baseline duration is determined based on the duration of all deviation events, and the deviation type is determined to be impulsive, drifting, or persistent based on the baseline duration, response time, and direction of change.

4. The method for controlling coarseness control of a vibrating screen in a coal washing plant based on wireless monitoring as described in claim 2, characterized in that, The process for determining whether an anomaly warning has been triggered is as follows: The cumulative number of times the deviation type is determined to be pulse-type is counted within a time period with the current sampling time as the end point and the length of the sampling window as the duration. If the cumulative number of times is greater than the total number of times it is determined to be pulse type within the sampling window, and it is not currently in the anomaly warning activation state, then it is determined to trigger an anomaly warning and is marked as an anomaly warning activation state; When the anomaly warning is active, if the cumulative number of occurrences falls back to less than or equal to the total number of occurrences identified as pulse-type within the sampling window, the anomaly warning is deactivated and the anomaly warning activation status marker is cleared.

5. The method for controlling coarseness control of a vibrating screen in a coal washing plant based on wireless monitoring as described in claim 3, characterized in that, The process for determining whether a drift warning has been triggered is as follows: Extract the absolute values ​​of all non-zero values ​​within the duration of the first deviation event in the observation window, and take the maximum value as the deviation magnitude. When the deviation type is determined to be drift type, if the deviation amplitude is greater than the difference between the upper and lower limits of the dynamic reference range of the corresponding signal, and the current state is not in the drift warning activation state, then the drift warning is triggered and marked as the drift warning activation state. If the deviation value corresponding to the deviation value that triggers the drift warning is greater than or equal to the preset confirmation time, then the drift warning is determined to be canceled and the drift warning activation status flag is cleared.

6. The method for controlling coarseness control of a vibrating screen in a coal washing plant based on wireless monitoring as described in claim 3, characterized in that, The process of determining the initial coarseness grade is as follows: Extract the absolute values ​​of vibration deviation, impact deviation, and current deviation at the last few sampling times in the observation window, and then calculate their average values ​​to obtain the mean values ​​of vibration deviation, impact deviation, and current deviation. Divide the vibration deviation from the mean by the difference between the upper and lower limits of the dynamic reference interval corresponding to the vibration signal to obtain the deviation ratio of the vibration deviation, which is denoted as the vibration deviation ratio. Similarly, the impact deviation ratio and the current deviation ratio are obtained; The weights are determined according to the process position type of the vibrating screen, and the vibration deviation ratio and the current deviation ratio are weighted and summed to obtain the comprehensive deviation index. Based on the comprehensive deviation index and the impact deviation ratio, the initial roughness level is divided into three levels: Level 1, Level 2 and Level 3.

7. The method for controlling coarseness control of a vibrating screen in a coal washing plant based on wireless monitoring as described in claim 6, characterized in that, The process of obtaining the final coarseness level is as follows: The average value of the feed rate of the upstream feeder within the observation window is taken as the current average feed rate; the upper and lower limits of the rated feed rate are obtained, and when the current average feed rate is greater than the upper limit or less than the lower limit, the feed rate is determined to be abnormal; The excess ratio is determined based on the proportion of particles exceeding the upper limit of feed size in the incoming material within the sampling window; the volume percentage of particles larger than the upper limit of feed size in the upstream incoming material at each sampling time is extracted and recorded as the excess ratio; when the excess ratio is greater than the excess proportion, the incoming material particle size is determined to be abnormal. If the initial coarsening grade is level two or three, and there are abnormalities in the feed rate or the particle size of the incoming material, the initial coarsening grade will be downgraded by one level and used as the final coarsening grade; otherwise, the initial coarsening grade will be used directly as the final coarsening grade.

8. The method for controlling coarseness control of a vibrating screen in a coal washing plant based on wireless monitoring as described in claim 7, characterized in that, Hierarchical control instructions include: When the final coarseness level is level one, the first control command is output to adjust the inverter output frequency and the excitation force of the vibrator. When the final coarsening level is level two, the second control command is output to reduce the feeding speed of the upstream feeder; When the final coarsening level is three, the third control command is output to drive the diversion flap valve at the discharge port to switch to the bypass position.

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