## 3 Novel Rotating Motion Mechanism
### Multi-Link Rotating Mechanism
#### 3.4.3 Multi-Link Crank Slider Rotating Mechanism  
[PERSON] et al. [129] designed a spacecraft module with a heavy-duty seven-degree freedom assembly robot, as shown in Figure 70. Propose a redundant configuration consisting of 3 mobile joints (prismatic joints) and four rotating joints, which combine high load, ample workspace, and flexibility. The working principle of this mechanism is as follows: the second and fourth rotating joints adopt a multi-link parallel crank slider mechanism, and the servo motor drives the ball screw to convert linear motion into rotational motion. The power is transmitted through a gear set and a rotary bearing to ensure high precision and stiffness. Adopting a redundant design of four rotating joints improves the ability to avoid obstacles and posture adjustment flexibility. This mechanism can achieve high load and high precision and is suitable for the precision assembly of heavy equipment. It has a large working range in a narrow space, and its foldable guide rail design supports movement inside and outside the cabin. This mechanism is suitable for precision assembly and handling large equipment in narrow spaces such as spacecraft cabins and submarines. The research status of the multi-link rotary transmission mechanism reflects the multi-dimensional integration of structural innovation and performance optimisation. Significant progress has been made in motion accuracy, load capacity, and spatial adaptability. Taking the dual four-bar rotary transmission mechanism as an example, it addresses the intermittent motion problem of traditional non-servo tool changing devices through the \"dual four-bar alternating drive\" strategy and the \"crescent-shaped\" trajectory design, achieving continuous rotation output in a compact space. However, due to the limitations of trajectory speed ratio control, there remains room for improvement in its motion accuracy and speed. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Types** & **Advantages** & **Disadvantages** & **Applications** \\ \hline Double four-bar rotary transmission mechanism [127] & The structure is simple, the space is compact, the cost is low, and the output disk rotates continuously & Limited motion accuracy, speed, and rotation angle & Automatic tool changing systems for machining centers and tapping machines \\ Cam five-link mechanism [128] & High reliability, compact structure, high precision, and stability & The design is complex, the cost is high, and the ability to dynamically adjust is limited & High-dynamic industrial scenarios such as packaging machinery and medical production lines \\ Multi-link crank slider rotating mechanism [129] & High carrying capacity, high precision, and flexibility & Complex structure, low speed, and accumulated errors & Gyroscope, low speed, high precision, redundant degree of freedom scene \\ \hline \hline \end{tabular}
\end{table} 
Table 14: Comparison of different multi-link rotary mechanisms. Figure 70: 7-DOF assembly robot (The red box represents a prismatic joint). The cam five-bar mechanism, combined with cam profile and geometric constraints, has been validated for error robustness through Monte Carlo analysis in high speed dynamic scenarios (average angle error < 0.003\({}^{\circ}\)), significantly enhancing transmission smoothness and production efficiency. Nevertheless, the lack of complex cam design and dynamic adjustment capabilities limits its widespread application. The multi-link crank slider mechanism achieves high load (heavy equipment assembly) and high precision coordination in the narrow space of the spacecraft cabin through a redundant configuration (3 moving joints + 4 rotating joints) and a folding guide rail design. However, the accumulated errors and low speed characteristics caused by structural complexity still require further optimisation.