## 2 Characteristics of the Structure of HAAS for Deep, Fully Mechanized Roadways
### Working Principle of the Support  
The new type of HAAS for fully mechanized roadways coordinates with devices such as roadheaders and anchor-drilling machines during roadway excavation. In addition, it mainly completes the actions of column lifting and lowering, movement and support under the control of the hydraulic control system, and the advance support can realize rapid movement and large-scale support. The specific working state is as follows.  
1. After the roadheader finishes a cutting, under the control of the hydraulic system, the column cylinder of the front support contracts. In this way, the lower column rises, while the upper column falls. Ultimately, the column of the front support separates from the roof and the floor (Figure 2a). 2. Then, the column cylinder of the front support maintains the contraction state. During this process, the advance support underpinned by the rear support pushes the front one forward to the target position with the aid of the hydraulic system (Figure 2b).  
Figure 1: Schematic diagram of the new type of HAAS for fully mechanized roadways.  
Figure 2: Working process of the new type of HAAS for fully mechanized roadways. (**a**) Support preparation; (**b**) Front support movement; (**c**) Front support expansion; (**d**) Rear support retracted; (**e**) Rear support movement; (**f**) Rear support expansion.  
3. While the front support moves to the target position, its column cylinder extends through the hydraulic system. Subsequently, the lower column falls to the floor, and the upper column rises to the roof, thus completing the support for the roof (Figure 2c). 4. The column cylinder of the rear support contracts under the control of the hydraulic system. Thus, the lower column rises, while the upper column falls. Ultimately, the column of the rear support separates from the roof and the floor (Figure 2d). 5. The column cylinder of the rear support maintains the contraction state. Meanwhile, through the hydraulic system, the advance support underpinned by the front support pushes the rear one forward to the position nearest to the front support (Figure 2e). 6. The column cylinder of the rear support extends with the assistance of the hydraulic system. By doing so, the lower column of the rear support falls to the floor, and its upper column rises to the roof. As a result, a whole movement process of the advance support is completed (Figure 2f).  
In this way, whenever the roadheader performs an excavation for a certain distance, the new type of HAAS simultaneously advances for a corresponding distance in an alternating way, closely following the roadheader. The specific working state provides timely support for the newly exposed roof after the roadheader excavation and prevents the loosening and caving in of the roof. Furthermore, it improves the support conditions of the end of the roadheader and effectively protects the safety of equipment and personnel. Additionally, the utilization of the hydraulic support for excavation not only leaves relatively sufficient space for parallel operations of multiple anchor-drilling machines, but also reduces support time, thus creating conditions for the rapid advance of the working face. If the floor undulates, the lower column of the support will be adjusted to a different floor-touching height; if the roof inclines, the upper columns on the left and right sides of the support will be altered to different roof-connecting heights. Hence, the new type of HAAS preferably accommodates the floor undulation of the roadway and the change in roof-dip angles.