# Design and Experiment of Dry-Ice Cleaning Mechanical Arm for Insulators in Substation
## 3 Mechanical System of Electrified Dry-Ice Cleaning Robotic Arm
### The Realization of Mechanical System of Mechanical Arm  
According to the insulation coordination standard for high-voltage transmission and transformation equipment in China, the safe distance between high-voltage lead and electrified part of the equipment in the experiments is shown in Table 1[42]. From Table 1, it can be concluded that the safe distance required for 200 kV is 1.5 m. The mechanical arm shall not only consider the realization of movement function, but also design for considering the problem of high-voltage-insulation resistance. The safe distance to the ground for 220 kV electrified working shall not be less than 1.5 m. In the actual cleaning operation, when the end-nozzle is at the highest point of the insulator, it is closest to the electrified body. Therefore, it is required that the distance between the end and the conductive body of the robot should not be less than 1.5 m. In order to ensure the high-voltage-insulation ability of the mechanical arm, the material of MC nylon with good insulation performance, high strength, and processability is used for the arm. At the same time, the bolt material is PPS (polyphenylene sulfide) nonglass fiber or Peek (polyetheretherketone). The three-dimensional model of the mechanical system of the mechanical arm is shown in Figure 5. The parallelogram \(P_{A}\) is composed of the main arm, auxiliary arm, forearm, and auxiliary arm driving rod. The parallelogram \(P_{B}\) is composed of the main arm, rear attitude linkage, attitude tripod, and arm base. The parallelogram \(P_{C}\) is composed of the forearm, front attitude linkage, attitude tripod, and nozzle. Thus, the arm of the mechanical arm is constructed. The main arm motor drives the driving shaft of the main arm to adjust the attitude of the main arm through the synchronous belt; the auxiliary arm motor drives the driving rod of the auxiliary arm to rotate through the synchronous belt to change the shape of the parallelogram \(P_{A}\), and then adjust the attitude of the small arm; under the combined action of the main arm motor and the auxiliary arm motor, the front and back, up and down movements of the end nozzle are realized. The parallelogram \(P_{B}\) and \(P_{C}\) are passive structures, keeping the attitude of the end nozzle unchanged and are always in a horizontal state. In order to balance the eccentric load moment caused by the gravity of the arm, a constant-force air spring is installed between the arm base and the main arm to reduce the driving force required by the main arm motor. The azimuth motor drives the arm base through synchronous belt to drive the whole arm to rotate horizontally relative to the mobile platform. This paper mainly studies the electrified dry-ice cleaning mechanical arm. For the convenience of the test, the mobile platform adopts two omni-directional wheels and two fixed castors to support, which can realize the omni-bearing movement of the whole mechanical arm in the substation. At the same time, the mobile platform can carry the dry-ice conveyor. The main arm motor, auxiliary arm motor, and azimuth motor are all composed of servo motor and planetary reducer. The motor, which is equipped with an incremental digital encoder, and zero position sensor compose a half-closed-loop control system. Considering that if the external ice conveying pipeline will be hardened due to the low temperature effect of dry-ice, which will affect the operation flexibility and strength of the robot, the robot would make full use of its own structural characteristics. A double row of independent dry-ice conveying pipeline is designed in the main arm, the forearm, and the joint, so that the dry-ice can enter from the bottom of the main arm to the end of the spray gun. Since the parts of the engineering prototype are all formed by mechanical processing, some right-angle areas will be formed in the dry-ice conveying circuit, which will have some blocking effect on the transport of dry-ice particles gas and a lot of impact on the cleaning effect.