## 4 SPL between Different Steps of Intelligent Mining and Backfilling Operations for the Whole Face  
### Division of Sequential Actions of the Intelligent Backfilling Operation for the Whole Face  
The overall cycling operation time of the backfilling working face includes the cycling time of coal mining and backfilling operations. The coal mining by the coal shearer can be considered as a continuous operation. The time it takes is relatively short compared with the hydraulic support motion process, hydraulic support adjusting process, dumping process, and tamping process. Therefore, the cutting depth and mining height of the coal shearer have little impact on the sequential operation time of the solid backfilling working face. However, the length of the working face is the main factor affecting the cycling operation time. It determines the advance length that can be achieved daily. According to the working face length and the cycling operation time of the backfilling process, three shifts of production (18 h) are usually arranged per day with one shift for maintenance (6 h) or two shifts for production (16 h), with one shift for maintenance (8 h). Therefore, the maximum shutdown time, i.e., maintenance time, of the backfilling working face per day is 6-8 h. The daily advance length that can be achieved is mainly determined by the cycling time of the backfilling process. For the whole backfilling working face, the optimal operation implies achieving parallel, autonomous execution of the mining and filling processes through the shearer, scraper conveyor, hydraulic supports, and perforated bottom discharge scraper conveyor. For this purpose, one should ensure that the equipment and mechanisms executing different mining and filling processes do not interfere with each other and fulfill specified functions in a spatially and temporally organized manner. The spatial sequence refers to an appropriate spatial alternation of processes executed by different equipment at different frame positions in the working face. Temporal sequence refers to the chronological order of specific processes involving different mechanisms within a specific frame, which are organized temporally to complete the mining and backfilling operations. Based on the above principles, this study designed the cyclic parallel mining and backfilling operations in the fully mechanized mining face, as shown in Figure 6.  
It is easy to see that the operation cycle is divided into distinct stages. Representative time points demarcating different stages are chosen as the benchmarks for analysis: 23:52 (end-oblique cutting knife stage), 00:14 (cutting triangular coal stage), 00:32 (end-brake bottom coal-cleaning stage), and 01:13 (central coal-cutting stage). Over the longitudinal section of the working face, we can divide the mining and intelligent solid backfilling operation cycle into four distinct stages. Thus, we obtain the relationship between the spatial positions of the equipment executing the corresponding processes at different stages, as shown in Figure 7.  
Figure 6: Illustration of the cyclic parallel mining and backfilling operations in the intelligent backfilling face. Figure 7: _Cont._  
1. End-oblique cutting knife stage: When the shearer moves to the end of the working face, the hydraulic support behind it follows the shearer and moves to the position of the rear drum. The scraper conveyor follows accordingly, and a curved segment for oblique knife-cutting is formed at the end. The shearer moves reversely, obliquely cutting the coal bodies ahead via the curved segment. As the end-oblique cutting knife stage is completed, the backfilling operation is orderly. The perforated bottom discharge scraper conveyor dumps the backfill material in groups, followed by tamping by the tamping mechanism. 2. Cutting triangular coal stage: Following the end-oblique cutting knife stage, the supports, located from the end of the working face to the position of oblique knife cutting, push the scraper conveyor forward to form a straight line.