Detailed Description
As shown in fig. 1, the belt conveyor is driven by a traction motor 5, and the power of the traction motor 5 determines the running speed of the belt conveyor. The traction motor 5 is electrically connected to the frequency converter 2, and the frequency converter 2 controls the working frequency of the traction motor 5. The frequency converter 2 may be frequency-controlled by a technician at a local console 1, and more advantageously by a ground control device 4. The frequency converter 2 communicates with a ground control device 4 via an optical cable 3.
Fig. 2 shows the structure of the frequency converter 2 in fig. 1 and the frequency conversion principle. The frequency converter 2 is an electric energy control device that converts a commercial power supply into another frequency by the on-off action of a power semiconductor device. The equipment converts a power frequency power supply (50Hz or 60Hz) into alternating current power supplies with various frequencies through a frequency converter so as to realize the variable-speed operation of the traction motor 5. The frequency converter 2 includes:
a rectifier converting the alternating current from the power grid transformed by the transformer into direct current;
an inverter for inverting the direct current to an alternating current;
and a direct current intermediate circuit for smoothing the output of the rectifier, wherein the direct current intermediate circuit can be a sine filter. Because the inverter generates rectangular waves which are the superposition of sine waves and higher harmonics and are directly acted on the motor to damage the motor or improve the withstand voltage grade of the motor, and the utilization rate is low, a filter circuit consisting of a capacitor and an inductor is additionally arranged behind the motor to eliminate the harmonics and shape the rectangular waves into approximate sine waves.
And the control circuit controls the rectifier, the inverter and the direct current intermediate circuit, and the control method is application control or direct torque matrix control (DTC).
Fig. 2 shows only one example, and the frequency converter 2 may also be a vector control frequency converter, which needs to perform a large amount of operations, and may further include a CPU for performing torque calculation and some corresponding circuits as needed.
The output of the frequency converter 2 is connected to the supply frequency of the stator winding of the motor, so as to achieve the purpose of speed regulation. With the development of industrial technology, the variable frequency speed regulation can optimize the speed regulation performance and save energy and reduce consumption, so that the application and popularization of the variable frequency technology in the field of coal mines can not only obviously improve the performance and the automation degree of electromechanical equipment of coal mines, but also realize energy conservation and efficiency improvement and reduce the cost per ton of coal, and has great economic and social benefits for coal mine enterprises. At present, the coal mine frequency conversion technology is mainly applied to fully-mechanized coal mining machines, frequency conversion three machines, shuttle cars, continuous mining machines, belt sealing machines, pressure pumps and other equipment.
Referring to fig. 1 again, the frequency conversion device of the centralized control belt conveyor comprises a nuclear balance 8, the nuclear balance 8 is installed above a tail 9 of the tail belt winch 7, and the nuclear balance 8 is used for monitoring the coal flow on the tail belt conveyor 7 and transmitting a coal flow signal to the ground centralized control center 4 of the belt conveyor through an optical cable 2.
According to the prior art, the control frequency conversion signal for the automatic frequency conversion operation of the belt conveyor cannot be derived from the load of the belt conveyor, and other detection means should be adopted. As the main conveying system of the mine is generally a plurality of belt conveyor machines, a nucleon scale can be arranged on each tail belt conveyor to monitor the coal flow on each tail belt conveyor and transmit a coal flow signal to a belt conveyor ground centralized control center.
The tail adhesive tape machine is as follows: since the belt conveyor is installed in the mine from the main adit (inclined outlet or main vertical shaft bottom yard) to the working face and extends forward with the development of the well field, the belt conveyor at the inclined outlet in the main adit is generally called the first belt conveyor, so that the last belt conveyor is directly connected with the fully mechanized mining face transfer conveyor or continuous mining face feeding crusher, and in fig. 2, only two belt conveyors are shown, the last belt conveyor 7 and the first belt conveyor 7-1 are shown.
First embodiment
As shown in fig. 3, the method of the present invention comprises:
step 1: detecting the coal flow at a distance S from the head of the belt conveyor;
and S can be determined according to the belt speed of the belt conveyor. In coal mines, the belt speed V of the tail belt conveyor 7 is typically about 4 m/s with a nominal load of 3000 tons/h. A belt scale (e.g., a nuclear scale) is mounted on the final belt conveyor 7 to measure the coal flow, and the position of the belt scale is at a distance S from the head, preferably S =240 seconds. Thus, the time difference t = S/V =240/4=60 (second) =1 (minute) when the coal flow of the same part passes through the belt weigher and the belt head, and the coal flow signal is transmitted to the belt machine ground centralized control center 4 through the optical fiber. Of course, the distance S of the belt scale from the head may vary depending on the application.
On one hand, the tail adhesive tape machine 7 can always adopt a power frequency (50 Hz) driving mode to prevent the occurrence of the accident that the tail of the adhesive tape machine is buried.
On the other hand, the end tape machine 7 may be driven by frequency conversion as needed. If the conveying capacity is larger than the maximum productivity of the working surface when the tail sealing-tape machine is operated at power frequency, the operation frequency of the tail sealing-tape machine is reduced to a reasonable value. For example, if the actual conveying capacity of the end tape machine 6 at industrial frequency is 2200 tons/hour, and the instantaneous maximum production of the working surface for which the conveying task is performed is 1600 tons/hour, the rotation speed of the end tape machine can be reduced by 20%, i.e., the operation frequency of the end tape machine 7 can be 40 Hz. The specific reduction ratio can be set according to production needs.
Note that, although the coal flow rate is measured by a tool such as an electronic scale, the coal flow rate = an instantaneous coal flow rate × a belt conveyor speed. That is, when a certain belt conveyor accelerates, the coal flow rate flowing out from the unloading part of the head of the belt conveyor is increased in proportion to the belt speed (assuming that the coal flow rate on the belt conveyor is uniform), so when the control system predicts that the coal amount of the last belt conveyor is increased through the electronic scale, the control system must synchronously pre-accelerate all the belt conveyors in proportion to the coal amount increase within a preset time, and ensure that the acceleration speed of each upper belt conveyor is not less than that of the next belt conveyor, so as to prevent coal pressing or coal spraying accidents at the tail of each belt conveyor.
The principle of the invention is to control the frequency of the next belt conveyor 7-1 by detecting the coal flow on the belt conveyor at a distance S from the machine head, and comparing it with a threshold value. That is, the centralized control center 4 sends out an instruction in advance (generally, the advance time can be controlled to be about 1 minute to eliminate the error between the running speed signal and the actual speed and other errors) when the suddenly increased or decreased coal flow is about to reach the head of the tail belt according to the coal flow rate in a distance from the belt scale to the head of the tail belt 7, correspondingly increases or decreases the motor frequency of the next belt 7-1 in series to increase or decrease the operation capacity of the next belt in advance, and ensures that the next belt can adapt to the requirement of the coal flow rate change in time.
Step 2: adjusting the operating frequency of the next belt conveyor based on the comparison of the measured coal flow rate and the threshold;
the centralized control center 4 converts the coal flow signal into a main belt conveyor running frequency signal. After the centralized control center device 4 collects the coal flow rate signals on the belt conveyor at the tail part, the belt conveyor running frequency under different coal flow rates is determined in the same proportion according to the relation between the belt conveyor running frequency and the coal flow rate, namely according to the rated load when the belt conveyor runs at the power frequency (50 hz), and the coal flow rate value is converted into the main belt conveyor running frequency value.
For example, when the rated load is 3000 tons/hour when the belt conveyor is operated at commercial frequency, the coal flow rate corresponding to 40hz, which is 80% of the commercial frequency, is 0.8 × 3000=2400 tons/hour, so that the belt conveyor operation frequency value can be calculated based on the coal flow rate value, and when the condition is satisfied (the belt speed is adjusted up or down), the operation frequency value is automatically input into the belt conveyor operation frequency control frame, and the belt conveyor operation frequency can be automatically adjusted immediately.
In the actual process, in order to ensure the normal operation of the system, a margin is generally left or a corresponding coefficient is multiplied according to different conditions and operation conditions of the belt conveyor, the coefficient setting can be considered to be generally between 1.1 and 1.2, coal scattering can be caused if the coefficient is too low, and the margin coefficient of the belt conveyor is too large if the coefficient is too high, so that electric energy waste is caused.
More preferably, the present invention further comprises step 3: when the coal flow rising change value exceeds a certain range, correspondingly increasing the rotating speed of the adhesive tape machine;
this is because, considering that the coal flow is constantly changing, frequently adjusting the rotation speed of the belt conveyor has no great practical significance, an amplitude limit value should be set, and for example, when the predicted rising change value of the coal flow exceeds 10%, the rotation speed of the belt conveyor should be automatically adjusted up by 10% immediately. Besides the tail adhesive tapes, the speed of the main adhesive tape conveyors connected in series needs to be increased synchronously, and the belt speed or the conveying capacity of the former adhesive tape conveyor needs to be higher than that of the latter adhesive tape conveyor.
More preferably, the present invention further comprises step 4: when the coal flow rate reduction change value exceeds a certain amplitude and lasts for a certain time, correspondingly reducing the rotating speed of the belt conveyor;
compared with the belt speed up-regulation of a belt conveyor, the belt speed up-regulation device has the advantages that the descending only meets the requirement of energy conservation, and the phenomena of coal flow congestion, coal scattering and the like cannot be caused by delaying the descending. Considering that the yield of the working face is reduced or stopped in a short time (for example, a slight pause phenomenon occurs in the coal cutting process of the coal mining machine), the belt speed of the belt conveyor is not reduced, so that the condition that the belt speed is immediately adjusted upwards after the belt speed is reduced is avoided. The key point of the belt speed downward regulation of the belt conveyor is that only part of working faces are in production to cause coal flow insufficiency, part of working faces are in production to cause yield reduction and the like, and various light load phenomena which cause the belt conveyor to be long in time are caused, for example, the coal flow reduction duration of the belt conveyor exceeds 2 minutes, and the reduction range is minimum to exceed 10%, and at the moment, the rotating speed of the belt conveyor is required to be automatically reduced. The belt speed downward regulation amplitude of the belt conveyor is also regulated with the coal flow, and downward regulation requires synchronous downward regulation of the main belt conveyors connected in series, and the belt speed or the transport capacity of the former belt conveyor should be kept higher than that of the latter belt conveyor.
Second embodiment
In a second embodiment of the present invention, a different method is used to control the frequency of the tape machine. The method of the second embodiment comprises:
step 1: the coal flow is measured at intervals at the head S of the belt conveyor. The measurement method in this step is the same as that in the first embodiment, and is not described herein again.
The coal flow signal reading interval delta t is set in relation to S, belt speed, and coal flow. The smaller the Δ t interval, the more accurate the measurement of the coal flow on the belt machine and the more precise the control of the belt machine. Generally, the faster the belt speed, the greater the coal flow, and the smaller the interval Δ t.
Step 2: calculating the coal flow distributed from the S position to the belt conveyor head to obtain a coal flow sequence, and selecting a maximum value Qmax;
qmax is the maximum value of the coal flow distributed on the section of the belt surface which is cut off from the head of the belt conveyor as the starting point to the tail of the belt conveyor in the direction S. Assuming that the coal flow signal reading interval is set to Δ t =10 seconds, the distance of the nucleon balance from the tape head is S =270 meters, the coal flow measured during a 10S period is Q =2000 tons/hour, the operation speed of the end tape machine is V =4.5 meters/second, and the coal flow advances by 10 × 4.5=45 meters over a period of 10S, so that the coal flow at 45 meters at 10 seconds is 2000 tons/hour. When the coal flows pass through the nuclear balance, the dynamic position of the coal flows on the belt conveyor can be calculated, so that the dynamic distribution condition of different coal flows on the belt conveyor at intervals of 10 seconds after the nuclear balance is obtained, as shown in fig. 4.
The first calculation method for calculating the maximum coal flow Qmax within the length of S is:
1) at the beginning, Qmax =0, the first time the coal flow Q1 is measured at S;
2) after an interval Δ t =10 seconds, the coal flow rate Q1 traveled V Δ t =4 × 10=40 meters < S (270 meters), Qmax was the maximum of 0 and Q1, it is clear that Qmax = Q1, the coal flow rate sequence on the belt conveyor is Q1 and Q2 which was just measured;
3) repeating the above steps until the 6 th time interval when the earliest measured Q1 traveled to the head over 6 10 seconds (4 x 10 x 6=240 meters), the existing coal flow sequences on the belt conveyor measured at this time were Q1, Q2 … Q5 (Qmax was the largest of the 5 coal flows), and the just measured Q6;
4) after the interval Δ t =10 seconds again, Q7 was measured, the first measured Q1 traveled 240+4 × 10=280>270 meters, Q1 had flowed out of the taping machine head, when the existing sequences on the taping machine were Q2, Q3 … Q6 (Qmax was the largest of the 5 coal flows), and Q7 just measured.
In essence, from the length S, the belt speed V, several coal flow sequence values within the length S can be determined. However, in practice, the belt speed varies, which affects the value of the coal flow rate, and when the same coal flow travels to different positions on the belt conveyor, the coal flow rate also varies with the variation of the belt conveyor operating speed. That is to say the values of the coal flow series are dynamically changing. The coal flow value is in direct proportion to the running speed of the belt conveyor.
For example, the nucleon balance measures that the coal flow value of a certain part on the belt conveyor is 2000 tons/minute, the running speed of the belt conveyor is 4 meters/second, and after the coal flow runs on the belt conveyor for a period of time, the running speed of the belt conveyor is reduced to 2 meters/second, and the coal flow value of the certain part is changed to 2000 × 2/4=1000 tons/minute. Thus, for each measured coal flow Qn, its distance traveled = current distance + current belt speed Δ t. A distance of travel greater than S indicates to run out of the tape machine, and Qmax is not counted in the next measurement.
And step 3: measuring the coal flow Q1 at the position of the length S away from the head of the belt conveyor, comparing the coal flow Q1 with the maximum value Qmax, and adjusting the running frequency of the belt conveyor in the next step according to the comparison result;
and automatically adjusting the running frequency of the motor of the next belt conveyor according to the coal flow Q1 at the length position from the tail belt conveyor head S. If Q1 is greater than Qmax, the motor frequency of the next belt conveyor is automatically increased according to the size of Q1, and the increased frequency value is in direct proportion to the coal flow value.
In addition, because the coal flow of the belt conveyor is changed all the time and the nuclear balance measures the dynamic coal flow, the numerical jump is large, and the meaning of frequently adjusting the frequency of the next belt conveyor is not large, the frequency is adjusted only when the exceeding amount exceeds a certain range, such as the exceeding amount reaches more than 10 percent, so as to eliminate the influence of the jump of the measured value. In actual production, the jump range of the reading of the electronic scale is still larger, the change of the coal flow is not obvious when the electronic scale is observed, and the influence of jumping of the coal flow value can be eliminated by adopting an average value method, for example, the average value is taken as the change basis of the coal flow, wherein the average value is one section every 10 s.
For the coal flow on the belt conveyor, for example, gradually reducing to a certain extent, such as the Q1 reduction extent exceeds 10%, and Q1< Qmax, the running speed of the belt conveyor at the lower part is automatically reduced according to the Q1 value reduction proportion.
Third embodiment
In a third embodiment of the present invention, a different method is used to control the frequency of the tape machine. The method of the third embodiment comprises:
step 1: the coal flow is measured at a distance S from the head S of the belt conveyor.
Advantageously, a belt conveyor may be employed to measure, continuously monitor the flow of coal therethrough in real time.
Step 2: calculating the coal flow distributed from the position S to the belt conveyor head to obtain the coal flow value on the belt surface;
the belt conveyor collects the coal flow value at a certain moment, so that the coal flow value on the belt surface with the length S can be obtained by integrating the moment value in time.
And step 3: comparing the coal flow value with a threshold value to adjust the working frequency of the next belt conveyor;
generally, the frequency value of the next belt conveyor is in direct proportion to the coal flow value, and since the coal flow of the belt conveyor is changed all the time and the nuclear balance measures the dynamic coal flow, the value jump is large, and the significance of frequently adjusting the frequency of the next belt conveyor is not great. Therefore, the frequency can be adjusted when exceeding a certain range, such as exceeding amount of more than 10%, so as to eliminate the influence of jump of the metering value. The specific method is the same as in the second embodiment.
In this way, for the next belt conveyor, the running frequency of the belt conveyor is adjusted in advance by predicting the coal flow change situation coming from the tail of the belt conveyor in a future period of time (such as predicting the coal change situation within 5 minutes), so that reasonable centralized control of a plurality of belt conveyors is realized.
In addition, the tail sealing-tape machine is preferably selected to be a crossheading sealing-tape machine close to the working face, so that all crossheading sealing-tape machines and all roadway sealing-tape machines behind the tail sealing-tape machine can realize variable-frequency operation.
It should be noted that, because the frequency converter driving the frequency conversion of the belt conveyor consumes electric energy, the starting point value of the frequency conversion drive of the belt conveyor should be set, for example, the frequency conversion drive can be adopted when the coal flow is below 90% of the rated value of the belt conveyor, for an inclined drift or inclined shaft with a larger angle, the starting point value of the frequency conversion drive of the belt conveyor should be lower, for example, the frequency conversion drive can be adopted when the coal flow is below 80%.
Fourth embodiment
In the present embodiment, a preferred technical method is described to improve the above centralized control method.
The threshold value in the foregoing embodiment may be set by the load (current value or active power) or the operating frequency of the next tape machine. If the carrying capacity of the next belt conveyor can be loaded with the upcoming coal flow, the operating frequency of the next belt conveyor does not need to be increased. But rather the question whether to reduce the frequency. That is, the threshold is variable and can be modified.
1. Correcting the operating frequency of each belt conveyor according to the current load of the belt conveyor
When the main tape conveyor is too long, for example, 8 tape conveyors are used in total, and the total tape surface of the tape conveyor is 12Km, a calculation error may occur. Therefore, the operating frequency of each belt conveyor can be corrected according to the current load, namely the current value or the active power of the belt conveyor.
If the loading capacity of a certain lane belt conveyor (the energy-saving effect of the lane belt conveyor is more obvious) is 50% of the rated value during power frequency operation, when the operation frequency is 25Hz, the belt conveyor is in a full-load state, the belt conveyor does work at the moment, and the current value or the active value of the motor is reduced to a desired value (mainly depending on the reduction of the additional load generated by the belt surface of the belt conveyor due to speed reduction). If the current value or the active value of the motor after frequency conversion is larger than a first expected value, the coal on the belt surface of the belt conveyor can be judged to flow fully, the risk that the coal overflows the belt surface exists, and the frequency conversion value is adjusted. Correspondingly, if the current value or the active value of the motor of the belt conveyor after frequency conversion is lower than a second expected value, the frequency conversion value of the belt conveyor is adjusted downwards, wherein the first expected value is larger than the second expected value.
2. And a belt scale is additionally arranged at a proper position of the adhesive tape machine to correct the calculation accuracy.
For example, a belt conveyor with a total length of 12km measures the coal flow at 6km, obtains an actual value, compares the actual value with a previous calculated value, and takes a larger value. The reason should be analyzed and corrected when the difference between the two is large for a long time.
When the coal flow is too small and is reduced to a certain value, a part of the motors can be automatically stopped to reduce the reactive loss.
In addition, when it is necessary to simultaneously speed up a plurality of sealing-tape machines, the speed-up amount of the former sealing-tape machine is larger than that of the latter sealing-tape machine, and the speed-up time of the former sealing-tape machine is slightly earlier than that of the latter sealing-tape machine, so as to prevent the coal piling phenomenon.
Fifth embodiment
The automatic frequency conversion can also be realized by adopting a sectional frequency conversion method, for example, the main belt conveyor shares the coal amount of one fully mechanized coal mining face and two tunneling faces. When the fully-mechanized mining face stops producing and the tunneling working face is still producing, the coal flow is very small, so that the conveying speed of each main belt conveyor can be automatically adjusted downwards according to a stop signal of the fully-mechanized mining face crossheading belt conveyor, for example, the motor is adjusted downwards to be 20 Hz.
Sixth embodiment
And the belt conveyor at each part can be started and stopped automatically along the coal flow. Because the coal flow change on each belt conveyor is predicted in advance, when each working face starts to produce, each belt conveyor can be started again when the coal flow is about to reach the machine head of the belt conveyor, for example, the belt conveyor is started 1 minute in advance, and the belt conveyor is stopped automatically immediately when the coal flow is exhausted, so that the idle running phenomenon is avoided.
In order to predict the control time point more accurately, the time point of the coal flow of each belt conveyor to arrive or the time point of emptying can be predicted according to the time point of starting or stopping of the adjacent belt conveyor in the coal direction of each belt conveyor and the running speed, so that the accurate automatic starting or stopping is realized.
In summary, the invention automatically reads the coal flow values of different periods on the last belt conveyor of the plurality of belt conveyors connected in series through the metering devices such as the nuclear balance, and calculates the travel distance of the coal flow on the belt conveyor at each period according to the equivalent value of the running speed and the length of each belt conveyor, thereby obtaining the coal flow dynamic distribution condition on each belt conveyor.
According to the coal flow dynamic distribution condition on each belt conveyor, the coal flow change trend about to enter each belt conveyor is pre-judged, the variable frequency control instruction is appropriately sent in advance according to the coal flow about to be increased or decreased, the running speed of each belt conveyor is increased or decreased in advance, the operation performance of each belt conveyor can be matched with the changed coal flow in time, and the effects of ensuring production, saving electric energy, reducing abrasion and the like are achieved.
According to the centralized control method. Referring to fig. 1 again, the centralized control system and core of the belt conveyor of the invention is that a belt scale and a control device 4 are additionally arranged on the belt conveyor, and the belt scale and the control device interact with a frequency converter 2 and a traction motor 5. The nucleon scale is arranged at a distance S from the machine head of the belt conveyor and is used for connecting the measured coal flow to the control device 4 through an optical cable. The control device 4 receives the coal flow measured by the nucleon scale, and calculates to obtain a calculated coal flow; and adjusting the working frequency of the next belt conveyor according to the comparison between the calculated coal flow and the threshold value. After calculating the adjusted working frequency value, the control device 4 sends the working frequency value to the frequency converter 2, and the frequency converter 2 drives the traction motor 5 to change the working frequency. The specific adjustment is as described in the above parameter method embodiment.
Briefly, in one embodiment, the control device 4 calculates that when the calculated coal flow rate increase or decrease change value exceeds the threshold value by a certain amplitude, the frequency converter 2 correspondingly adjusts the operating frequency of the next belt conveyor up or down.
In another embodiment, the nucleon balance calculates the coal flow at intervals of time Δ t at a length S from the head of the belt machine. The control device calculates the coal flow distributed from the position S to the belt conveyor head to obtain a coal flow sequence, selects the maximum value Qmax of the coal flow as the calculated coal flow, and measures the coal flow Q1 at the position of the length S from the belt conveyor head as the threshold value. The maximum coal flow Qmax is obtained by dynamic calculation of the belt speed of the belt conveyor, and the interval time delta t is determined by the belt speed of the belt conveyor, the length S and the coal flow.
In another embodiment, the control device calculates the coal flow rate distributed from the position S to the belt machine head after detecting the coal flow rate at the position S away from the belt machine head, and obtains the coal flow rate value on the belt surface as the calculated coal flow rate.
In another embodiment, the control device corrects the operating frequency of each belt conveyor according to the current load of the belt conveyor and sends the corrected value to the frequency converter, and the frequency converter controls the operating frequency of the belt conveyor through the traction motor according to the corrected value.
In yet another embodiment, the control means calculates: if the current value or the active value of the motor of the belt conveyor after frequency conversion is higher than a first expected value, the working frequency of the belt conveyor is adjusted upwards; and if the current value or the active value of the motor of the belt conveyor after frequency conversion is lower than a second expected value, the working frequency of the belt conveyor is adjusted downwards, wherein the first expected value is larger than the second expected value.
In a further embodiment, a plurality of belt scales may be provided, each mounted in an intermediate position of the current tape machine, each connected to the control system by optical fibres. The control device obtains the actually measured coal flow, compares the actually measured value with the measured coal flow, adjusts the working frequency of the current belt conveyor according to the larger value of the actually measured value and the measured coal flow, and sends the adjusted value to the corresponding frequency converter.
The present invention is not limited to the above-described embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention are intended to be equivalent substitutions and should be included within the scope of the present invention.