## 2 The Development of Typical Rotating Motion Mechanisms
### Ratchet and Pawl Mechanism
#### 2.5.3. New Ratchet Mechanism for Multi-Material Additive Manufacturing Technology  
[PERSON] et al. [89] proposed a novel flexible ratchet mechanism that utilises additive manufacturing techniques for various materials, as shown in Figure 39. This design eliminates the general movement of springs, claws, or gears in traditional ratchet and pawl mechanisms. The organisation uses 3D printing technology to replace conventional mechanisms with multi-material mechanisms that combine the principles of flexible mechanisms and classic ratchet mechanisms, allowing parts to move in one direction while preventing movement in the opposite direction. This behaviour is obtained through elastic deformation, which transfers the displacement of the component to the flexible area during insertion. In contrast, the geometric shape of the ring allows for limiting the displacement of the element in the opposite direction. [PERSON] et al. [94] conducted innovative research on the design optimisation of rotary motion mechanisms. They proposed a dual-mode ratchet mechanism with 12 and \begin{table}
\begin{tabular}{c c c c c} \hline
**Types** & **Core Innovation** & **Advantages** & **Disadvantages** & **Applications** \\ \hline Traditional ratchet & Single pawl, fixed & Simple structure and & High noise and poor & Low speed and low \\ mechanism & tooth pitch & low cost & performance & load scenarios \\ Modular ratchet & Multi-disc, & High load capacity, & Manufacturing is & High speed pulse \\ mechanism & multi-pawl, and elastic tooth design & low noise & complex and costly & transmission, heavy \\ Micro ratchet & Miniaturisation and & Miniaturisation and & Low load capacity & Micromechanical \\ mechanism & elastic rod design & low friction & and easy failure & system \\ \hline \end{tabular}
\end{table} 
Table 8: Comparison of ratchet mechanisms for high speed transmission. Figure 39: The prescribed boundary conditions for (**a**) insertion and (**b**) locking direction of the flexible ratchet mechanism model. 24 teeth based on the modular combination principle, as shown in Figure 40. The mechanism has constructed a motion transmission system with self-locking characteristics through the coordinated cooperation of the driving unit, compression spring, and locking pawl. The spring element achieves dynamic meshing control between the pawl and ratchet, effectively reducing motion impact through an elastic energy storage mechanism. The rapid prototyping of the mechanism was achieved using fused deposition modelling (FDM) additive manufacturing technology, with polylactic acid (PLA) and acrylonitrile butadiene styrene copolymer (ABS) as forming materials. The experimental results show that this design combines lightweight and low noise characteristics and reduces manufacturing costs by about 68% compared to traditional machining processes. Through the collaborative optimisation of tooth profile parameterisation modelling and material mechanical properties, researchers have established a quantitative relationship model between tooth number, contact stress, and fatigue life, verifying the trade-off law that increasing the number of teeth can improve transmission stability but sacrifice compactness. This technical solution is particularly suitable for rapid concept validation of low torque applications such as small electromechanical equipment and automation instruments. Its modular design concept provides an effective technical path for the iterative development of customised motion mechanisms. Table 9 summarizes and compares the transmission performance of different 3D printed ratchet and pawl mechanisms mentioned above.