The application of the fuzzy controller for tension system control of the scraper conveyor in the mines

The tension control of the automatic adjustment system of the scraper conveyor used for the initial tension of the chain of the scraper conveyor. A hydraulic control system was developed in accordance with the principle, and a theory of system control was created. The controller with a Fuzzy-PID controller used in the automatic tuning system was designed to limit the minimum tension point to a certain specified area. Modeling has shown that it is possible to avoid an increase in power loss due to higher tension and chain exit from the sprocket due to lower tension.


Introduction
As the load on the scraper conveyor becomes greater and the length becomes longer, the dynamic characteristics have an obvious influence on the performance of the drag conveyor [1,2]. And then this will lead to instability and reduced reliability of the scraper conveyor [3][4][5]. Especially the dynamic chain tension among other dynamic behaviors plays an important role in improving the performance of the scraper conveyor. In this article, it is mainly considered the principle of the selfadjusting system for chain tensioning, as well as analysis methods and related control theory to ensure efficient operation of the scraper conveyor [4,6]. The hydraulic systems were to control the tension of the scraper conveyor [8]. Moreover, the scraper conveyor was speed controlled by two PMSM motors with high stability, using the adaptive PSO-Fuzzy logic controllers [11] and the adaptive PSO-Bacterial foraging optimization speed stability control algorithm [12].
The load on the working surface of the scraper conveyor changes depending on the position of the shear (plow), and also changes the resistance to the conveyor and the tension in the chain, which leads to a change in the elastic lengthening of the conveyor chain [11]. Theoretical analysis proves that the elastic elongation of the chain of a heavy-duty 240(m) scraper conveyor is almost 0,8 m between idle and heavy-duty [13]. If the elastic elongation of the chain cannot be compensated for overtime, the tension at the point of minimum tension of the conveyor chain will decrease, even zero tension will appear. Both theories and experiments have proven that the initial tension of the scraper conveyor has IOP Publishing doi: 10.1088/1757-899X/1159/1/012018 2 a great influence on its running characteristics and resistance [6]. If the initial tension is too low, the operation will be unstable and the chain jump phenomenon will sometimes occur, causing the chain to get stuck and broken. In an accident, the initial voltage caused excessive resistance, resulting in high power consumption [2]. This paper presents a Fuzzy-PID controller that controls the tension of the chain conveyor under the impact of starting and stable working of the system in two cases of direct start and two-speed starting anti S type.

Conveyor pretension and minimum tension
The distribution of the chain tension during the operation of the scraper conveyor Figure 1 shows the dotted line is the initial, and the solid line is the tension distribution during operation, i S is the tension at each point during stable operation, 0i S corresponds to the initial tension, and : At the moment, the system has the lowest elastic elongation.
If the elastic coefficient k of the chain elasticity is constant, the elastic prolongation under pretension 01 S is: After the stable operation, the elongation is distributed along a solid line, then the elastic elongation at this time: that the elastic elongation of the system is the smallest, which is the optimal configuration of the conveyor power. For conveyors without automatic tension control, in order to make the tension at the point of minimum tension greater than zero during operation, the following must be done: Equations (5) and (6) are the initial voltage value when the engine power ratio is a specific value. When 2 2 min S S   =     is substituted, the pretension is determined without an adjusting device, 2 min S       is the minimum allowable value for the point of minimum tension.

Principle of automatic pretension of the scraper conveyor
The principle of automatic adjustment of the conveyor tension is to compensate for the tension change caused by elastic elongation (or contraction) of the chain by varying the distance between the two sprockets to achieve the goal of limiting the tension to a minimum tension point within a certain range. A scraper conveyor running on a working surface can change the center distance of two sprockets only due to the hydraulic cylinder pushing the sprocket and the drive element on the housing due to the limited space. Figure 3 shows the principle of scraper conveyor tension control. Voltage signals A S and B S are output by the sensor detection system, A S and B S are calculated after analyzing and filtering the signals [8].
The actual value is then determined using the "Comparator I" signal to determine the difference between A S , B S and the expected delta value. The "Comparator II" signal determines if there is; whether the product exceeds the acceptable error value and outputs the trigger value. The values are given according to the following formula: The actual value is then determined using the Comparator I signal to determine the difference between A S , B S and the expected delta value. The "Comparator II" signal determines if there is The hydraulic control system that implements the principle of Figure 3 is shown in Figure 4. The number "1" in the figure indicates the oil pump; the "2" is a group of bypass and safety valves; the "3" is a two-position two-way electromagnetic; the "4" solenoid proportional valves; the "5" is an accumulator that stores oil under pressure; the "6" is a 2/2 ways valve; the "7" is a 3-position 4-way valve and the "8" is a pressure switch.  A simplified mechanical model of a drag conveyor with an electro-hydraulic automatic tension control system is shown in Figure 4, and the corresponding dynamic differential equation: If the process of adjusting the tension at the initial conditions of the conveyor is investigated, the problem becomes more complex, since the force at each point of the concentrated mass of the For formula (9), to take the Laplace transform, there is: . .
The change in chain tension:  Figure 5. System Control principles Figure 6. Block diagram of the tension control system In order to study the basic characteristics of an even more simplified control system, a simplified closed-loop control system is shown in Figure 5. The .  The pressure-flow equation of the electro-hydraulic servo valve is:

Design Fuzzy-PID controller for scraper chain tension
The pressure-flow equation for the cylinder is: In the above formulas: , In the simulation analysis i F and i F * are used as detection signals, target value ( ) 21.000( ) In the previous section, we studied the control method of the pretension of the scraper chain and constructed the mechanical and mathematical models of the control in its simplified form. However, due to the large frictional resistance of the nose and the tail, the nonlinearity of the chain stiffness and the material. The non-uniform nature of the distribution, in fact, this control system has nonlinearity and time-varying. In order to better solve such control problems, The Fuzzy-PID control applies to this system, and now its principle is briefly described. Figure 7 is the fuzzy adjustment PID controller structure.  Create the dynamic differential equation of the whole system and combine the equations (8) and equations (13) -(17) to obtain the dynamic response of the system. The scraper conveyor system was a model on Matlab-Simulink R2018b software. The scraper conveyor system parameters [13][14][15][16] are described and programmed to calculate the output parameters, as shown in Figure 8 to Figure 16. Figure 8 to Figure 10 shows the forces of chains at point 2 in Figure 1. Figure 8 shows that during the start according used to the PID controller forces of chains, the scraper conveyor tension fluctuates IOP Publishing doi:10.1088/1757-899X/1159/1/012018 8 strongly to a peak of value 2.45.10 5 (N). The oscillating force fades out after 3 cycles and stables a time of 1.25 seconds with an around the value of 2.1.10 4 (N). When starting the scraper conveyor using the Fuzzy-PID controller for forces of chains. The forces of controlling the load tension are stable with decreasing fluctuation after 3 cycles, and then stable after 0.38 seconds at value 2.1.10 4 (N) in Figure 9. Comparing the tension control of the scraper conveyor with the PID controller and the Fuzzy-PID controller, the results clearly show that the Fuzzy-PID controller gives much better quality in Figure  10.      Figure 11 shows that the start according used to the PID controller for the hydraulic cylinder, the speed of the hydraulic cylinder large fluctuations to a peak of value 1.41(m/s). The velocity of the piston gradually stops after 7 cycles and stables a time of 10.25 seconds with an around the value zero. But when starting the scraper conveyor with the Fuzzy-PID controller for forces of chains. The velocity of the piston is decreasing fluctuation after 3 cycles and a peak of value 0.11(m/s), and then stable after 5.8 seconds at an around the value zero in Figure 12. Figure 13 compares the piston velocity between the PID controller and the Fuzzy-PID controller, the results show in detail that the Fuzzy-PID controller gives better control quality and is more reliable.    Figure 1 to stretch the chains of scraper conveyor, respectively. Figure 16 compares the thrust of the piston between the PID controller and the Fuzzy-PID controller, the results show that thrust of the piston the Fuzzy-PID controller gives better control quality and is more reliable. It can also be seen from the figure that the system tends to be stable after

Conclusion
The principle of automatic adjustment of the pretension force of the scraper conveyor chain has been studied and the hydraulic control system has been developed. The system control theory is an analysis and the Fuzzy-PID controller is applied to the control system and simulation is performed. The simulation results clearly show that the Fuzzy-PID controller is capable of automatically stabilizing the tension of the chains of the scraper conveyor. The process of controlling the chain tension of the chains via the Fuzzy-PID controller, which adjusts the hydraulic valve opening, controls the scraper conveyor to operate stably, less vibration, friction between the chains, and the upper surface. In addition, the conveyor tension control system helps to reduce chain jam, gear breakage, reduce the