## 1 Introduction  
Live-line operation and maintenance have been extensively performed in power systems because the aging phenomena of the electrical power equipment become severe while the cost of power interruption continuously increases [1; 2; 3]. The live-line teleoperated robots gradually replace the manual transmission line and substation operation because the manual operation is risky for the personnel and inefficient for the line and substation equipment maintenance [4; 5; 6]. Since the 1980s, [PERSON] et al. developed the first generation of master-slave live-line operation robots Phase I; the operator was required to operate the robotic arm in the insulating bucket at the end of the lifting mechanism to complete the live-line operation task [7]. Then, the Phase-I robot was modified and upgraded to Phase II by integrating the machine visual system, automatic tool switch device, and human-machine interface. The Phase-II robot could complete all operation tasks at the same insulation level as Phase I with the semi-automatic operation strategy [8]. [PERSON] et al. compared the performances of the teleoperated manipulators with and without a haptic device, and they concluded that the task completion time reduced when the haptic generated the force [9]. The aforementioned live-line teleoperated robots adopt the independent insulation layer connected to the robotic arm to provide body electrical isolation. This method has reliable insulation performance for the transmission live-line operation because the insulation layer is thick enough to ensure sufficient leakage distance to prevent flashover under the contaminated conditions. Therefore, the structure of the system is excessively large and complicated for the substation equipment maintenance with limited operating space. This paper proposes a design scheme of a self-insulating joint as a wrist in the robotic arm based on the cable-driven parallel-series (CDPS) mechanism to control the motion in four degrees of freedom (DOFs). The CDPS design can provide more than one DOF to improve the flexibility of the joint, which facilitates the robotic arm to accomplish complicated live-line operation in a restricted workspace. The mechanism separates the motors and actuators from the joint to realize the remote driving. The electrical insulation is integrated into the joint to reduce the volume and complexity of the mechanics. The CDPS was initially used to mimic the movement of the human neck. In 2007, [PERSON] et al. proposed a mechanism to simulate a human cervical vertebra by a compression spring and the muscles of the neck by cables. This model provided an approximate equivalent calculation method for the lateral bending of the flexible spring [10]. Then, [PERSON] et al. focused on the low-noise humanoid neck robot and investigated the CDPS with a flexible spine support. The paper also optimized the mechanism design and analyzed the workspace [11]. [PERSON] examined a similar model by replacing the flexible spine with a rigid spine and optimized the cable force distribution [12]. [PERSON] et al. modified the CDPS mechanism by adding two concentric shafts connected with a universal joint in the spring to restrict the lateral bending motion of the spring and simplify the model. The concentric shafts are driven by the motor in the mechanism to provide the yaw motion [13]. [PERSON] and [PERSON] considered multiple CDPS mechanisms as the wrist, elbow, and shoulder joints to compose a seven DOF robotic arm [14; 15]. The dimension of a cable-driven parallel system was then optimized based on tension distributions [16; 17; 18]. [PERSON] conducted further research to minimize the consequences of cable failure by generating a wrench opposite to the motion direction [19; 20; 21]. In 2019, the CSPS mechanisms are used for the rehabilitation and under water applications due to their intrinsic flexibility and adaptability [22; 23].