Design and Simulation of Autonomous Up-and-down System for Transmission Line Live Operation Robot with the UAV Assistance

Aiming at the current bottleneck problem that restricts the practical application of robot system engineering in transmission line live operation, in order to improve the on-line and off-loading efficiency of live working robots on transmission lines and improve the practical level of the robot system as a whole, this paper proposes a design and operation method of autonomous on-line and off-loading mechanism of double-arm live working robots based on UAV assistance. Firstly, the realization process of autonomous up-and-down of the robot was analyzed, based on which the structure of the auxiliary hook of the up-and-down system and the lifting winch were designed. Then, the force analysis was carried out on the up-and-down process of the robot, and the appropriate winch drive motor was selected through theoretical calculation. In order to ensure the rationality of the up-and-down process, the operation motion planning was carried out on the up-and-down of the robot. Stress analysis and simulation were carried out on the maximum load bearing point of the auxiliary hook and the walking wheel mechanical arm under different states, and the results showed that the hook and the robot arm could meet the requirements of the robot loading and unloading, and the whole robot loading and unloading system was designed reasonably. Compared with the traditional loading and unloading system designed in this paper, the loading and unloading efficiency could be improved. It has important theoretical significance for the development of the physical system of robot uplink and down.


Introduction
Transmission line live operation robot [1][2][3][4] is an intelligent equipment for transmission network maintenance, but how to achieve efficient and stable on-line operation of robots has always been one of the bottleneck problems plaguing the practical application of robots.Since the on-line and off-line robots [5][6][7][8] have not been effectively solved, the overall operational efficiency of robots has been seriously affected.At present, most of the live work robots on the line rely on manual lifting, a small part of the use of on-line devices and other methods, specifically, mainly divided into three types, one, through the lifting mechanism to transport the robot to the operation point, relying on the pole and tower operators to adjust the direction of the robot placement, the robot placed in the transmission line operation point; Second, the robot and the operator are jointly delivered to the top line by the ladder truck, and then the transmission line robot is manually operated by the staff.Third, the robot is lifted to the power line by using the on-line device or related auxiliary platform, but the operator still needs to place the robot on the power line.The above three methods need to power off the transmission line in advance or operate on the ground line, which is difficult to meet the requirements of live work.Therefore, how to efficiently achieve live work is a key point in the field of practical application of live work robots.Current research shows that manual hoisting is still the most important way to go online.Although manual hoisting can effectively bring robots online, its low efficiency and high risk seriously affect operation efficiency, and online auxiliary devices are not widely promoted and applied, and have high requirements on terrain and high cost.Based on this, this paper proposes a method of using UAV-assisted hook to hang wires and lifting winch to collect and release insulated ropes to complete autonomous up-and-down of robots.Compared with manual lifting method, this method not only improves efficiency but also reduces labor intensity and risk of manual up-and-down wires, which lays a theoretical foundation for the development of physical system for robot up-and-down wires.At the same time, it has important theoretical significance and practical application value for promoting the practical process of robot.

System Design of UAV Assisted Autonomous Up-and-down System
Robot automatic up-and-down system is essentially a lifting mechanism, the purpose is to enable the robot to achieve independent up-and-down without manual assistance, so as to save manpower and reduce risks.The autonomous up-and-down system designed in this paper adopts the method of UAV-assisted hook hanging.The robot is connected to the insulation rope below the hook through the lifting winch machine, and then realizes the operation of up-and-down wire by rotating the winch drum.After the completion of up-and-down wire, the end claw of the robot arm is used to complete the hook picking and placing, as shown in figure 1.It is necessary to consider the friction caused by the robot's own weight and the air insulation rope in the process of loading and unloading, and select a suitable lifting motor based on the numerical model of the robot's speed, acceleration and power during the process of ascending and descending to ensure that there is enough driving force to realize the robot's autonomous launching and smooth rolling off the line.The main structure design of the whole upper and lower wire system includes the design of the auxiliary hook and the design of the lifting winch.

Stress Analysis of Robot Hook on and Off Line
In the process of robot autonomous online hook mainly has the following states: (1) The static state of the hook on the transmission wire after the UAV is mounted on the hook; (2) the state of the robot hanging below the winch after the robot is connected to the insulation rope below the hook; (3) the state of the robot accelerating, that is, the actual force of the insulation rope under the hook is greater than the gravity of the robot itself, and the acceleration of gravity is added after the grid division is completed.Then the stress simulation analysis can be carried out by applying fixed constraints and boundary conditions to the moving blocks of the model.When the UAV is mounted on the hook and reaches the power line, the insulation rope below the hook is in the state of free hanging, and the stress analysis is carried out on it in Workbench software.The deformation is shown in figure 2 (a), and the equivalent stress is shown in figure 2 (b).The overall self-weight of the two-arm robot is about 70kg, and two hooks are needed to pull the robot at the same time.The force of the insulation rope under one hook is about 343N, so a force load of 343N is applied under the insulation rope.The deformation is shown in Figure 2 (c), and the equivalent stress is shown in figure 2 (d).When the acceleration of the robot is 0.9m/s2, the force calculation of the insulated rope shows that the tension of the rope is 375N, and the deformation is shown in figure 2  According to the deformation and stress distribution analysis in figure 2, the greater the stress on the insulation rope, the greater the corresponding deformation of the internal stress of the hook.Meanwhile, regardless of the stress, the maximum stress generated inside the hook is in the middle of the hook.Therefore, the density and hardness of the middle of the hook should be strengthened when selecting materials to ensure the strength of the hook during the process of loading and unloading.The values generated by the hook in different states are shown in table 1.Through the analysis of table 1, it can be seen that as the gravity under the hook gradually increases, the maximum shape variable and the maximum stress also increase.The maximum shape variable and the maximum stress under the hook are 0.46099mm and 147.57MPa respectively when the robot is accelerated.Through calculation, the gravity under the hook and the maximum shape variable and the maximum stress of the hook show approximately linear changes.It can be seen that the stress change of the hook bearing point is consistent with the stress of the robot in the process of loading and unloading.Therefore, the system structure design is reasonable and effective.

Conclusion
Based on the analysis of on-line and off-line process of double-arm live working robot, an autonomous on-line and off-line method based on UAV is proposed, and the solid model of auxiliary tools such as auxiliary hook and lifting winch is designed.The stress simulation is carried out on the stress point of the auxiliary hook and the walking wheel manipulator arm.The simulation results show that the hook designed according to the principle of up and down line is subject to the maximum stress and the maximum shape variable under the maximum stress, which meets the stability and operation motion requirements of the up and down line process.The research in this paper has important theoretical significance and practical application value for the practical application of the dual-arm robot.

Figure 1 .
Figure 1.Schematic diagram of unmanned aerial vehicle (UAV) double-arm live working robot on line.

Table 1 .
Maximum shape variable and maximum stress under different states of the hook.