# Horizontal Bending Angle Optimization Method for Scraper Conveyor Based on Improved Bat Algorithm
## 1 Introduction  
The scraper conveyor is one of the key equipment for underground coal mining [1]. It not only transports coal, but also provides the running track of the shearer and the positioning of the hydraulic support. It is the connection point of the fully mechanized mining equipment [2; 3]. In the fully mechanized mining face, the middle slot of the scraper conveyor is pushed by the hydraulic support to the coal wall by a step (the length of the step is usually 600-1000 mm), which is pushed to the next cutting plane. At the same time, the adjacent middle grooves will be driven by each other and rotated to form a transition section. To ensure the stable operation of the scraper conveyor, the transition section will form two anti-symmetrical bending lines. This horizontal bending section presents an S shape, hence it is called the S-bending area [4]. The angle between the adjacent middle grooves of the S-bending area of the scraper conveyor is called the horizontal bending angle. The horizontal bending angle of the S-bending area of the scraper conveyor is selected from 1\({}^{\circ}\) to 3\({}^{\circ}\), and the horizontal bending angle used under the mine is usually determined empirically.  
Previous research on scraper conveyor has mainly focuses on the monitoring [5; 6] and calculation [7; 8; 9] of running load, dynamical problems [10; 11; 12], friction and wear [13; 14; 15]. However, studies rarely account for the effect of the horizontal bending angle of the S-bending area on the additional resistance, the running load, the production energy consumption ratio, the mean time between failures (MTBF) of the mining equipment and the shear cutting efficiency has been rarely investigated. In fact, if the horizontal bending angle of the S-bending area is improperly selected, the additional resistance will increase [16], the middle groove and the sprocket assembly will be seriously worn [17], the current fluctuation is large, the energy consumption of the mining equipment is high, the equipment service life is low and the MTBF is small.  
Bat Algorithm (BA) was proposed by [PERSON] in 2010 based on swarm intelligence [18; 19]. It simulates bat behavior, which avoids obstacles, detects preys and locates the roosting crevices in the dark. Based on the bionic principle, BA simulates the optimization and search process with a population bat individual movement processes and searches for the prey [20; 21]. BA has the advantages of simple structure, few parameters, strong robustness, and is easy to understand and implement. Since the BA was proposed, it has been widely applied in construction machinery [22], finances [23], forecasting [24], etc. However, similar to other optimization algorithms, the basic BA also has the disadvantage of falling into local optimum.  
Considering the above observations, a method based on improved BA (MBA) for optimizing horizontal bending angle is proposed. The rest of this paper is organized as follows. In Section 2, the basic theory of the mathematical models of the running resistance of scraper conveyor and BA are described. Then, the MBA and the whole flow of proposed horizontal bending angle optimization scheme are illustrated in Section 3. Some simulations and analysis according to the actual working conditions of the fully mechanized mining face are presented in Section 4 to validate the superiority of the proposed method. In Section 5, a mine application is presented to validate the practical effect. In Section 6, some conclusions and outlooks are summarized.