## 2 Methods  
In response to the inspection needs in the cable tunnel shown in Figure 1, we have made a series of designs for this self-insulating mechanical arm. The design of the bionic insulation arm incorporates a tendon-driven mechanism to simulate musculoskeletal actuation, physically isolating conductive components (e.g., motors) from the arm's dielectric body. Both materials and structural design prioritize electrical insulation, ensuring full-body dielectric performance. The Mechanical arm employs a comprehensive 7-degree-of-freedom (7-DOF) linkage model to replicate the complex kinematics of human arm movements, comprising the following: \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Features** & **Mechanical Arm Type** & **Cables Repairing** & **Live Line Robot** & **Self-Insulating Type** \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Comparison of typical global-mapping-based range perception methods. Figure 1: Power cable tunnel hidden space environment. * Three DOFs at the wrist joint (enabling pitch, yaw, and roll);
* One simplified DOF at the elbow joint (flexion/extension only);
* Three DOFs at the shoulder joint (omnidirectional orientation). Design emphasis is placed on the 3 DOF mechanisms of the wrist and shoulder joints to maximize dexterity in confined spaces. To achieve the design target of self-insulation, the mechanical arm eliminates joint-mounted motors--a critical limitation in conventional designs. Drawing inspiration from musculoskeletal systems, we implement a tendon-driven parallel mechanism that replicates the full range of motion in both shoulder and wrist joints while maintaining complete electrical isolation. This biomimetic approach simultaneously decouples conductive components (e.g., motors) from the dielectric structure, preserves anthropomorphic flexibility through cable-pulley force transmission, and reduces inertial loads via distributed actuation. The resulting architecture combines the dexterity of human-like movement with the essential dielectric properties required for live-line operation. Since the mechanical arm requires self-insulating properties, conventional drive motors cannot be directly mounted on the joints. Therefore, this manuscript adopts a cable-driven mechanism to simulate the omnidirectional movement of the shoulder and wrist joints to achieve performance and flexibility similar to a muscle-driven system. As shown in Figure 2, the self-insulating mechanical arm consists of a 3-DOF biomimetic self-insulating joint serving as the shoulder and elbow, connected by a 1-DOF elbow joint. To mimic the three-degree-of-freedom (3-DOF) roll, pitch, and yaw movements of the human arm's shoulder and wrist joints, a biomimetic self-insulating joint mechanism was designed, as illustrated in Figure 3.  
Figure 2: Overall structure of self-insulating mechanical arm. The joint mechanism consists of a fixed platform and a moving platform. A concentric, self-insulating, flexible body is arranged to provide mechanical support. Two concentric shafts inside the flexible body further reinforce the structure, connected via a universal joint. The upper shaft, made of insulating material, passes through the upper platform. Thus, the moving platform is cable-driven and connected to the fixed platform via the self-insulating flexible body, providing support. A rotary bearing is also embedded between the universal joint support rod and the moving platform, enabling relative rotational motion between the moving platform and either the flexible body or the fixed platform. The rotating shaft restricts the lateral bending of the flexible body, effectively simplifying inverse kinematics modeling and computation. The upper and lower platforms are affixed with insulating plates to enhance electrical insulation. A combined bearing links the upper moving platform to the insulating plate, facilitating rotational and translational motions. The mechanism is driven by four cables, allowing the moving platform to achieve 3-DOF roll, pitch, and yaw movements under tension.