# Structural Design and Study of an Integrated Cutter System Based on Machine Operation
## 3 Evaluation and Decision Making for the Integrated Cutter System  
### Establishment of the AHP Evaluation System  
In the previous section, three types of cutter systems, including traditional cutter systems, were introduced in this paper. In order to objectively evaluate the best cutter system solution design out of these three solutions, this paper analyzed the indicators of the cutter system based on the AHP. A comprehensive score table was established so that the performance gaps between each cutter system could be visualized. As shown in Figure 7, the key to decision making for the cutter program through AHP lies in the establishment of an evaluation index system, i.e., clarifying the target layer, the criterion layer, the program layer and the relative weights among the criterion factors. For the target layer, the ultimate goal is to select the best cutter system. For the solution layer, it consists mainly of three different cutter systems. As for the criterion layer, this paper selected static strength, the disassembly process, gripping size, gripping quality, three-dimensional size and preload force as the criterion factors, and these indexes will be analyzed one by one in the following. Figure 5: Center integrated cutter system structure. Figure 6: Working principle of center integrated cutter system: (**a**) locked state; (**b**) relaxed state. (1) Static strength analysis  
Shield machine operation relies on the rolling cutter to cut and squeeze the rock to realize the tunneling function. During this period, the cutter system will be subjected to large impact loads and vibration, and it needs to ensure strong rigidity and resistance to deformation. In order to check whether the cutter structure meets the strength design requirements under severe working conditions, static strength analysis is an indispensable step. (2) Grab size and three-dimensional dimensions  
The internal space of the shield machine is shown in Figure 8. The cutter-changing robot is placed in a human cabin with a diameter of about 2 m. The length of its activity space is about 7 m. The length of its working area reaches 7.5 m, and the narrowest point in the width direction is about 0.8 m. The ratio of the cutter-changing robot in the horizon-tal and vertical directions is \(<\)1:9, which is a narrow and long characteristic. Therefore, in the process of the robot taking out the cutter, there are certain requirements on the size of the mechanism it grabs. (3) Grab quality  
Compared to manual cutter changing, the quality of the cutter system's grip will have a direct impact on the design of the robot. If the gripping quality increases, the robot will require more output power from the end gripping mechanism, the displacement mechanism, etc., resulting in an increase in the design size of the corresponding equipment in the small space of the shield machine. In addition, as the end load of the robot increases, its dynamics and trajectory planning conditions become more difficult. Therefore, the addition of extra gripping mass should be avoided as much as possible during the design of an integrated cutter system. (4) Disassembly process  
Since the TCS has the problem of cumbersome disassembly steps, the main purpose of the present design of the integrated cutter system is to simplify the disassembly steps of  
Figure 8: Space for cutter-changing robot. Figure 7: Analytic hierarchy process evaluation system. the TCS and to lay the foundation for the realization of mechanized automatic disassembly. Therefore, the disassembly process of the cutter system is an important index to measure its performance. (5) Preload force  
In threaded connections, it is common to apply a preload force to enhance the reliability and loosening resistance of the connection. As the cutter keeps cutting soil and rock during the tunneling process of the shield machine, the cutter structure is subjected to continuous impact and vibration, which very easily produces loosening phenomena.