Design of auxiliary robots for distribution network uninterrupted operation

: Here, the auxiliary robot for distribution network without power failure is designed. The robot includes the design of mobile chassis, turntable, tops, and legs. The mobile chassis is responsible for walking, power supply, and work safety support platform. It can walk flexibly and has a certain ability to overcome obstacles. The turntable not only can withstand axial and radial loads, but also can withstand tilting moments. Tops can provide reliable support and good insulation guarantee for work buckets. Outriggers serve to level out and ensure the stability of the vehicle. The experimental results show that the design of the network-assisted robot without power failure can meet the actual operation requirements.


Introduction
With the increase of users' time for power outages and the increasing demand of the state-grid corporation for non-blackout operations, the demand for distribution network non-blackout operations has gradually increased [1]. However, some operations are affected by topographic factors such as space size and ground levelling, and insulation cannot be used. The arm-in-arm trucks will not be powered off. If the insulated platform is used, the platform will be inconvenient to move and the height will not be enough. As a result, the uninterrupted power supply cannot be fully deployed. Therefore, there is an urgent need for a self-moving, small-occupying, and high enough insulation arm height. The operating robot capable of rotating 360 degrees provides an insulated platform to assist the uninterrupted operation.
The foreign manufacturers of high-altitude working machinery are mainly concentrated in developed countries such as Europe, America, and Japan. The high-altitude machinery products in each region have their own characteristics. European products have a variety of structural types. Aerial working machines can be divided into folding arms, telescopic arms, and hybrid arms according to the boom structure. Hybrid arms are particularly prominent. The European product operation has a full range of height specifications, with a minimum operating height of ∼10 m and a maximum height of >100 m. North American aerial vehicles are mainly insulated, accounting for about 65% of the total. This is because North American regulations and policies have insulation performance requirements for most high-altitude operations. Compared with Europe, the height of aerial working vehicles in North America is relatively low, and the maximum operating height of products is basically no >70 m. In order to ensure insulation performance, North American high-altitude vehicles generally adopt simpler structure types. Only low-level products and products with low insulation grades use high-complexity hybrid arm structures, and medium-height products use folded-arm structures and large height products use telescopic arm structure. Japanese aerial vehicles are widely used, especially the ordinary and insulated products are widely used. Japan's aerial work vehicles have a low operating height, and their compactness and flexibility are the main features [2].
The self-propelled models developed by domestic companies are mainly crank arms and straight arms. Hybrid arm models have not yet been developed. The main features of the product are the use of independent chassis and telescopic axle design [3,4]. The hydraulic system adopts electro-hydraulic proportional control technology. The electronic control system adopts CANBUS digital electronic control technology. China's aerial work platforms have made great progress. The former aerial work platforms were smallsized products. The product forms include hand-push type, scissor type, sleeve cylinder type, and mast type. Now, aerial work platforms are large-scale products. Product forms include selfpropelled, off-road, boom, telescopic arms.
At present, the power supply companies can carry out the normal tasks of live distribution line operations include: live off, connected to 10 KV overhead line leads, live repair overhead conductors, live replacement tool gates, live replacement linear insulators, live replacement of tensile insulators, live replacement poles, live line replacement, and other projects [5][6][7][8].
Due to the complexity of current distribution overhead lines and intensive equipment, problems such as the narrow operating range of live distribution and easy to cause personnel fatigue, coupled with the invisibility of high voltage and the operation of the operator at pole height, often There are some risk factors that can easily cause electric shocks at different potentials or other electrical equipment. Therefore, if the safety measures are incomplete, the operation methods are not standardised, and the tools are used improperly, single-phase grounding, phase-to-phase short circuits, and personal injury or equipment damage may occur. In addition, the quality problems in the safety protection tools and insulation shields used in distribution network live work may cause the insulation of the shield to fail to meet the requirements, which in turn causes creeping discharge or breakdown. At present, the manufacture of insulated tools is not a regular manufacturer, they are all in their own research and development, and there is not yet a comprehensive standard for improvement, this poses a certain safety risk to operators and equipment.
At present, China's insulation bucket car is basically obtained through the import method. China's self-produced insulation bucket car has certain defects, and the country's relevant regulations and standards have not yet been introduced. Therefore, only valid reference can be made by referring to the standards specified in IEC/TC78. After selection, it should also be tested accordingly.

Scheme design
According to functional requirements and with reference to the characteristics of inspection robots at home and abroad, a plan for assisting robots (hereinafter referred to as robots) with distribution network power supply is proposed, as shown in Fig. 1

Mobile chassis
The mobile chassis is mainly responsible for the running and steering of the whole machine and supports the components such as the turntable, power, hydraulic electrical system, and boom etc. It mainly consists of four solid tires, four traveling motors, four traveling speed reducers, steering cylinders and a bottom. The chassis material is Q345B and weighs about 2000 kg as shown in Fig. 2. The mobile chassis is the core component, and the chassis body adopts the H-shaped steel frame structure, as shown in Fig. 3. The chassis mechanism is mainly composed of a walking motor, a wheel, a steering motor, and a leg assembly. The motor drive is used for walking, which has the features of stable walking, timely response and low noise. The steering is hydraulically driven, reliable, and flexible.

Turntable
The turntable is connected with the frame through a slewing ring. The turntable carries the engine power system, hydraulic system, electrical control system, boom system, and covers, counterweights and other components. It consists of two left and right uprights and bottom plates. The material of the turntable is Q345B and weighs 1300 kg. As shown in Fig. 4.
After consulting related books, in accordance with relevant professional standards, the swing mechanism of the aerial work vehicle should be capable of 360° rotation in both forward and reverse directions. The rotation speed should be no >2 r/min, and the start, rotation, and braking should be stable, accurate, no shaking phenomenon, good fretting performance during the rotation process. The contact angle of a cylindrical roller is generally 45°, and the axes of two adjacent cylindrical rollers intersect at 90°. This not only allows the rotary device to withstand axial and radial loads, but also withstands overturning moments.

Determine the maximum load of the cylindrical roller:
Cylindrical rollers are subjected to three types of loading during operation, as shown in Fig. 5. The first is the axial force Q, that is, the vertical force, which is composed of the weight of the turntable and the lifting mechanism, the weight of the lifted cargo, and the inertial force of the lifting and lowering; the second is the radial force H, that is, the horizontal force, this force is generated by the centrifugal force of the lifting device and the rotary table, the wind load and the meshing force of the slewing gear; the third is the tilting moment Mov, which is caused by the eccentric action of the axial force and the radial force.
Two sets of cylindrical rollers that intersect in direction are represented by groups I and II. Assume that the number of cylindrical rollers in each group is half of the number and they are arranged one-to-one at intervals. This group of cylindrical rollers is the most stressed at point A, as shown in Fig. 6. The maximum normal load FImax of any of the cylindrical rollers is: In the formula: The force analysis of the inner ring, as shown in Fig. 7, can be obtained from the force balance conditions FIQ and FIH. In order to obtain FIM, the seat ring can be regarded approximately as a

Determine the allowable load of the cylindrical roller:
According to the Hertz formula, the line contact stress between the raceway and the cylindrical roller is: In the formula: F -normal load of the cylindrical roller on the contact line; E -The elastic modulus of the material. General raceway materials use carbon steel or low carbon alloy steel. Cylindrical roller materials use bearing steel, so it is desirable; L -Effective length of cylindrical roller and raceway, under normal circumstances desirable L = 0.85 d, m; ∑ ρ -The sum of the main curvature of the contact surface between the cylindrical roller and the raceway, ∑ ρ = 0.6; D -cylindrical roller diameter, m.

Tops system
The upper loading system consists of a basic arm, a telescopic arm, an upper folding arm, a lower folding arm, a telescoping mechanism, and a drag chain. The basic arm, the upper folding arm and the lower folding arm adopt a rectangular structure welded by four plates. The structure is simple and the welding process is good. The telescopic arm is made of a new type of composite material, FRP, which has excellent insulation properties and comprehensive mechanical properties, and can simultaneously meet the insulation and mechanical performance requirements under live working conditions. The welding boom is made of 70 steel, the basic arm mass is about 400 kg, the lower folding arm mass is about 300 kg, and the upper mass is about 200 kg. The telescopic mechanism adopts the telescopic cylinder method. Towline is a high-strength engineering plastic that is resistant to oceanic climate and adapts to the harsh working environment.

Determination of the range of motion of the lifting mechanism:
The lifting mechanism designed in this design includes four folding arms, a lower folding arm, a basic arm, and a telescopic arm. The lower end of the lower folding arm is hinged on the turntable and is driven by the lower arm cylinder; the lower end of the upper folding arm is hinged with the upper end of the lower folding arm and is driven by a brace hydraulic cylinder and a parallel four-bar linkage; the upper end of the upper folding arm is hinged to the rear end of the basic arm. It is driven by a boom cylinder and a parallel four-bar linkage. The telescopic arm is placed inside the basic arm and connected by telescopic cylinders. The end of the telescopic arm is articulated with the bucket and is supported by an exposed parallel four-bar linkage to maintain the level of the bucket. The range of motion of the upper and lower arms in the plumb bob is: The lower arm is relative to the turntable: 0-70°; the upper arm is relative to the lower arm: 0-140°.

Structural design and main dimensions of the boom:
The boom is subject to bending and torsion. In order to obtain greater strength and rigidity, a thin-walled box-shaped structure is generally adopted. In order to reduce the welding deformation, the arm frame is formed by two stamped and formed grooved plate butt joints, and the flanged plate flanges adopt a large rounded shape to enhance the local rigidity of the plate. In order to obtain a higher bending section modulus of the main bending section, the upper and lower stiffening ribs can be added to obtain a gradual state of equal strength stress. The boom section is shown in Fig. 8.
The boom height h can be determined by economic conditions (minimum structural mass): In the formula: Mthe maximum composite bending moment experienced by the boom; γ n -Thickness ratio of webs; After calculation, the cross-sectional dimensions of each boom are shown in Table 1.
From the total length of the chassis, the distance from the centre of the rear axle to the front end of the car, and the boom of the related aerial work vehicle as a reference, the length of the lower folding arm L1 = 2650 mm is finally determined; the length of the upper folding arm L2 = 2650 mm; the length of the basic arm L3 = 3020 m.

Outrigger mechanism design
The outrigger mechanism of the hybrid aerial work vehicle plays a role in levelling and ensuring the stability of the entire vehicle, requiring solid, and reliable operation.

Determination of leg span:
The legs of a folding boom type aerial working vehicle are generally arranged forward and backward, and project to both sides, as shown in Fig. 9.
The position of the supporting points in the vertical and horizontal directions of the support legs should be selected properly. The principle is that the stability of the vehicle should meet the specified requirements when the operating platform is used to calibrate the load and the maximum operating range.
In the formula: G 1 -Turntable gravity; G 2 -chassis gravity; G bboom gravity; q -operating platform gravity; Q -Operating platform calibration load; L 1 -the distance from the gravity centre of the turntable to the centre of rotation; r -the distance from the centre of gravity of the boom to the centre of rotation; Since the total vehicle width is B = 2000 mm and 2a > B, take a = 1000 mm.

Support foot grounding area determination:
In order to make the folding arm type aerial working vehicle work under the specified ground, the pressure will not sag and ensure that it can be reliably supported on different grounds. The support foot must have enough grounding area Sj to ensure the maximum support reaction force Fmax to the ground. The pressure is not greater than the foundation strength, i.e: In the formula: σ b -Foundation strength, generally 1.6 MPa.

Calculate operating conditions and load combinations
There are two main working conditions when the robot works, one is 'normal work' and the other is 'overload.' The type of load is mainly self-weight load, rated load, wind load etc. The specific parameters are shown in Table 2 below: State Description: Each of the above states corresponds to the first two types of operating conditions and load combinations, and the swing angle and swing angle of the work bucket must also be considered.

Theoretical basis for wind load calculation
When calculating wind loads in working conditions, consider the influence of different directions on the vehicle, and consider both positive and lateral directions.
among them: P w -wind load acting on the boom; C -Wind coefficient; q -Calculate wind pressure; A -Boom upwind area; 3.3 Calculate wind pressure q q = 0.625 v 2 = 100 N/m 2 (v < 12.5 m/s) In the formula: q -Calculate wind pressure, N/m 2 ; v -Calculate wind speed, m/s;

Calculation of windward area A
In the formula: A i -Calculated area of each section (forward and sideways); L i -the calculated length of each section of the arm;

Calculating wind load P w
In the formula: ∑ Ai -the calculated area of each section of the arm;

Simulation
In order to verify the feasibility of the design of unplanned working robots in distribution networks, relevant verifications were performed on the robots in the simulation environment. The verification is mainly divided into normal conditions and overload conditions. The following are simulation verification results. Figs. 10 and 11.

Conclusion
After the research and development of auxiliary robots for distribution network uninterrupted operation, through the theoretical analysis and internal simulation test, the design scheme of the assisted robot for distribution network without power failure was analysed and researched, and the prototype of the auxiliary robot with distribution network power failure was manufactured. The design of the robot includes four categories: mobile chassis, turntable, tops, and legs. The mobile chassis is responsible for walking, power supply, work safety support platform, flexible walking, with certain obstacle avoidance capabilities; the turntable can withstand axial and radial loads, but also can withstand tilting moments; tops can provide reliable support for the work bucket and good insulation guarantee; the leg mechanism from the levelling and to ensure the stability of the entire vehicle work, the design of the distribution network without power supply assisted robot can theoretically meet the actual requirements of different working conditions.

Acknowledgments
Thanks for the financial support of the State Grid Chongqing Electric Power CO, Electric Power Research Institute and State Grid Chongqing Electric Power Company.