## 2 The Development of Typical Rotating Motion Mechanisms
### 2.1. Gear Drive
#### 2.1.3 Magnetic Gear
[64] proposed a novel axial flux modulated superconducting magnetic gear (AFMSMG), as shown in Figure 22. Axial flux modulation superconducting magnetic gear (AFMSMG) uses superconducting block magnets (SBM) instead of traditional permanent magnets, utilising the high critical current density and ideal diamagnetism of superconducting materials to form a strong magnetic field at low temperatures. Through axial magnetic flux design, the interaction between the inner and outer rotor magnetic fields and the fixed modulation ring generates harmonic magnetic fields, achieving non-contact torque transmission with a torque density more than twice that of traditional magnetic gears. The non-contact transmission reduces wear, has a long lifespan, and is suitable for high precision applications. Superconducting properties are stable at low temperatures and ideal for unique environments. Cooling conditions below 77 K are required, which increases costs and system complexity. Compared to traditional solutions, the cost of superconducting materials and cooling systems is much higher. [PERSON] et al. [65] proposed an Axial Radial Cone Magnetic Gear (ARCHG) based on 3D printing technology, as shown in Figure 23. Using FeSiCr as the rotor and pole piece material, we explored three manufacturing methods: wire cutting, selective laser melting (SLM) hybrid manufacturing, and particle deposition modelling (PDM). Among them, PDM technology achieves the integrated moulding of complex conical magnets by compounding 95% MQP-S magnetic particles with 5% PA12 adhesive. Compared to traditional axial radial magnetic gears (ARMG), ARCHG shortens the magnetic flux path through a conical magnet structure, reduces volume by 52%, increases torque density by 28%, and simplifies assembly processes. The experiment showed that its gear ratio remained stable at 6.5, verifying its efficient transmission characteristics. However, introducing adhesives in 3D printing technology decreases magnetic flux density, and the magnetic barrier structure manufactured by SLM hybrid may increase magnetic resistance and leakage. This design is suitable for high precision, low vibration scenarios such as servo motors, robot joints, and customised industrial drive systems, especially for small batch production needs that require rapid prototyping or complex geometric structures. It provides a new solution for applying magnetic gears in precision engineering and green manufacturing. Figure 22: Topological Model of Axial Magnetic Flux Modulation Superconducting Magnetic Gear. Traditional metal gears continue to improve performance through tooth profile optimisation and parameter control. For example, high coincidence spur gears achieve high load and low vibration through multi-tooth meshing, but their tooth profile modification coefficients need to be precisely matched. The new biased worm gear transmission system adopts a line contact conjugate tooth surface design, which inherits the advantages of traditional worm self-locking while achieving flexible adjustment of axial position and simplified assembly; Noncircular gears exhibit unique advantages in dynamic variable speed scenarios by defining the gear ratio function through Fourier series and combining it