## 4 Common Driving Methods for Rotating Motion Mechanisms
### Hydraulic Drive  
A hydraulic drive generates force and motion by utilising liquid to transmit pressure within a closed system, achieving control and operation of mechanical devices [177]. The hydraulic system can carry large loads and achieve precise motion control. It can achieve seamless transmission, effortless operation, and fast response, and it can start at high speed and change direction frequently. Electro-Hydraulic Servo Drive  
[PERSON] et al. [178] designed and validated an integrated electro-hydraulic pump (EHP) based on an axial piston pump, as shown in Figure 92. The electro-hydraulic pump is driven by a brushless DC motor, which generates electromagnetic torque through three-phase back electromotive force to drive the rotor to rotate. The rotor drives the plunger to reciprocate and adjusts the plunger stroke through the inclined plate and valve plate to achieve periodic oil suction and discharge. The oil is distributed to the high-pressure chamber and low pressure chamber through the valve plate, and the movement of the plunger produces high-pressure oil output. The motor and pump share the same housing, eliminating the need for a drive shaft, dynamic sealing, and external leaks. Using hydraulic oil to cool the motor eliminates the need for traditional cooling fans and reduces noise and vibration. Figure 92: An EHP structure based on an axial piston. [PERSON] et al. [179] proposed a novel energy regenerative hybrid drive system (ERHD), as shown in Figure 93. By integrating the motor, hydraulic, and control modules, the recovery and reuse of braking energy can be achieved and applied to the roll transmission system of reversible rolling mills. During the start-up phase, the electric motor and hydraulic motor jointly drive the load, and the accumulator releases the stored hydraulic energy to assist in acceleration and reduce the load on the electric motor. The electric motor is driven separately in the constant speed stage, and the hydraulic module exits. During the braking phase, the hydraulic motor converts the kinetic energy of the load into hydraulic energy and stores it in an accumulator to achieve energy regeneration. In precision rotary motion mechanisms, hydraulic drive technology has become essential in high precision motion control due to its core advantages of high load capacity, seamless transmission, and fast dynamic response. In recent years, innovation in electro-hydraulic servo drive technology has significantly improved system integration and energy \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Types** & **Advantages** & **Disadvantages** & **Applications** \\ \hline Traditional hydraulic drive [177] & High load, precise movement, smooth operation, seamless transmission, and rapid response & Potential leakage risk, high maintenance cost, and loud noise & Scenarios that require high load and precise control \\ Electrohydraulic servo drive [178] & Small size, lightweight, high power density, low noise, good dispersion performance, high reliability & Insufficient oil absorption during high speed operation leads to reduced efficiency and vibration & Aircraft hydraulic systems require equipment in environments with sustained high-pressure or low noise levels \\ Electrohydraulic servo drive [179] & Energy regeneration, reducing the peak power and energy consumption of the motor, and cooling down & The system requires precise control, additional energy storage devices, and pipelines & High-inertia, frequent start-stop scenarios, green, and low-carbon industrial applications \\ \hline \hline \end{tabular}
\end{table} 
Table 21: Hydraulic drive comparison. Figure 93: Schematic diagram of ERHD driving system. efficiency: [PERSON] et al.