## 2 The Development of Typical Rotating Motion Mechanisms
### Chain Drive
#### 2.3.3 Polymer Material Chain Links Based on 3D Printing  
[PERSON] et al. [78] investigated the mechanical properties of four materials, including ABS, ABS Kevlar composite, PLA, and PETG, under tensile load through systematic experiments and finite element analysis, as shown in Figure 33. They also constructed an empirical mathematical model to quantify the influence of printing parameters such as link diameter, printing direction, and filling density on strength. The innovation lies in combining the optimisation of 3D printing process parameters with the comparison of multi-material properties, revealing the significant impact of printing direction on mechanical properties--horizontally printed chain links have nearly 9 times higher strength than vertically printed links due to the continuous distribution of material layers along the principal stress direction. Research has found that PETG material exhibits optimal performance in horizontal printing, with a fracture force of 300.8 N, far exceeding the 4.70 N of PLA. The positive control effect of extrusion temperature, filling density, and other parameters on strength has been verified through mathematical models. Compared to traditional metal chain links, polymer chain links have advantages such as lightweight, corrosion resistance, and insulation, but their mechanical strength is still limited to low-to medium-load scenarios, such as decorative chains, pet traction chains, or religious product suspension devices. However, their applicability under extreme loads is insufficient, and the strength of ABS Kevlar composite materials decreases due to weakened bonding between fibers and matrix interface, exposing material compatibility issues. Table 5 summarizes and compares the transmission performance of the different chains mentioned above. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Types** & **Advantages** & **Disadvantages** & **Applications** \\ \hline \multirow{3}{*}{Single-row chain drive [72; 73]} & Simple structure, easy maintenance, long lifespan, and low cost & High noise, lubrication required, low precision, and prone to vibration at high speeds & Bicycles, motorcycles, and other low load scenarios \\  & Strong load-bearing capacity, high material utilisation rate, and reduced mould stress concentration. & High requirements for processing equipment and precise control of parameters & Industrial machinery, long-distance or high load scenarios. \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Comparison of the performance of different types of chain drives. Figure 33: Appearance of a chain link made of ABS polymer material before (**left**) and after (**right**) fracture. Single-row chain transmission (such as a sleeve roller chain) has a simple structure, easy maintenance, and low cost. However, it has problems such as high noise, regular lubrication, and significant high speed vibration. It is suitable for low load scenarios such as bicycles and motorcycles; multi-row chain transmission optimises tooth profile through multi-tooth collaborative load-bearing and cold forging technology, significantly improving load capacity and material utilisation. However, it has strict requirements for machining accuracy and mold control and is commonly used in heavy load conditions of industrial machinery. Silent chain transmission achieves low noise and high efficiency through meshing optimisation, but is limited by the torque-carrying range and is specifically designed for high precision, high speed transmission in automotive engines, machine tools, and other applications. The bidirectional chain transmission adopts a phase difference dual chain design to suppress the polygonal effect, which has the advantages of high stability and lightweight. However, the complex structure requires high installation accuracy, making it suitable for precision transmission systems.