# A Digital Twin System for Adaptive Aligning of Large Cylindrical Components
## 3 Digital Twin Multi-Dimensional Modeling for the DT Aligning System
### Geometric Modeling for the DT Aligning System  
The geometric model is the main manifestation of studying the aligning process of large components. By establishing a 3D visualized DT model, it describes the geometric properties and motion structure of physical objects, ensuring that the DT model is highly consistent with the physical system in terms of size, material properties, shape, etc., while also reflecting the real assembly relationship and structural subordination relationship of physical objects. Therefore, based on the physical entity of the large component aligning system, a 3D visual virtual model is established to complete the geometric modeling. Specifically, the key transmission parts of the mechanism of the aligning system are retained, and the lightweight CAD modeling of the parts is carried out. Based on the topology model, the assembly structure tree is built to describe the motion structure and transmission relationship of the aligning system. Setting the material and color of the model provides a 3D visual operating environment for the simulation and monitoring of physical objects for the aligning system, as shown in Figure 5.  
* **Lightweight CAD modeling of parts**, in the various modules of the aligning system, there are a large number of small volume components and features (e.g., threads, rounded corners, and grooves) to be designs, which can lead to a sharp increase in the number of modeling grids. On the premise of retaining the key transmission relationships and dimensions of the aligning system, the non-essential components and features are simplified or ignored in accordance with the principle of the model being lightweight. For the posture-adjustment mechanism and guide rail mechanism, the synchronous belt, screw thread, pulley and other components are deleted and merged, and the chamfer features on the guide rail and other components are removed. For the air flotation mechanism, remove components, such as shaft sleeves, bolts, nuts, etc.
* **Establishing a topology assembly relationship:** from the kinematic perspective, the physical execution subsystem for the aligning system is a typical multi-body system; therefore, constructing a topological structure chain of the physical execution system can clearly express the relative assembly and transmission relationships between various components of the assembly. At the same time, to ensure that each component model corresponds clearly to the topology nodes, a tree structure is used to store and manage the topology chain during modeling. Importing CAD models as assemblies, the hierarchical nodes of each model are determined by the machine topology, and the 3D solid model is attached to the corresponding topology nodes.
* **3D visualization of geometric models:** according to the physical entity of the aligning system, the model color, material, and other geometric properties are customized. Color, map, and assign material balls to physical entities to change their material properties. At the same time, build a virtual environment scene, perform operations, such as graphics rendering, and restore the physical entity of the interconnecting system.  
Figure 5: Geometric modeling for the DT aligning system.