Development Of Wheel-legged Wall Climbing Robot For Welding And Dynamic Characteristic Research

To shorten welding cycle,reduce manufacturing cost,and improve production quality,on-site welding of large steel structure equipment has an immediate need of automation.Due to the operational flexibility of the wall climbing robot,combining automatic welding technology with wall climbing robot technology became an effective way to solve the problem of on-site welding.On the basis of summary and analysis of wall climbing robot techniques,an innovation wall climbing robot with wheel-legged mobile mechanism is developed,which can be used for on-site welding of large steel structure equipment.The related theories and techniques of the robot on principles of movement and adsorption,theoretical design and optimization,kinematic and dynamic modeling are researched in this paper.The configuration scheme of wall climbing robot is proposed,which combine the advantages of wheeled mobile mechanism,legged mobile mechanism,and non-contact permanent magnetic adsorption system.The configuration scheme can solve the contradiction between smooth movement and environmental adaptation,reliable adsorption and flexible motion faced by robot.The configuration scheme of welding actuator including two prismatic joints and two revolute joints is proposed in order to achieve flexible and precise control of the welding torch.The body structure of the wall climbing welding robot is designed based on the above configuration schemes.The performance of the robot on adhesion,mobility and environmental adaptation are analyzed in order to verify the rationality of the structure design.The performance of the permanent magnetic adsorption system is related to the stability,adaptability and flexibility of the wall climbing welding robot.By analyzing the stable attachment conditions of the robot during obstacle crossing and wall transition,the minimum adsorption force requirement of permanent magnetic adsorption system and the adsorption design value of permanent magnetic adsorption units are obtained.The magnetic circuit structure of permanent magnetic adsorption unit is designed,and the structural parameters and position parameters are optimized by the finite element method.Based on the internal-balance theory,a non-linear spring mechanism is designed.The elastic force of spring mechanism is used to balance the adsorption force of the central permanent magnetic adsorption unit,so that the screw can be driven easier.Kinematic and dynamic modeling is the basis of motion control for wall climbing welding robot.Considering the particularity and complexity of the robot structure,the robot is divided into the part of welding actuator and the part of wheel-legged mechanism.For the welding actuator,the kinematic model is established by the Denavit-Hartenberg method,and the forward-inverse kinematic solutions are derived.For the wheel-legged mechanism,the kinematic model is established by the Sheth-Uicker method.The solutions of kinematic unknown parameter and the equations of inverse kinematic are derived.On this basis,the kinematic model of the whole robot system is established by the velocity vector method.For the composite motion of the robot during obstacle crossing and wall transition,the constraint equations are derived based on the kinematic model,and the dynamic model is established by the Routh method.Based on this model,the driving torque relationships between leg joints and wheels are analyzed.For the skid-steer of the robot on the wall,the distribution of supporting forces on driving wheels is analyzed.The friction characteristics between driving wheels and wall are analyzed based on the discretized tire model of automobile dynamics.Then the dynamic model is established by the Newton-Euler method.Based on this model,the change rules of kinematic and dynamic parameters during robot steering on the wall with different inclinations and structural parameters are analyzed.Finally,the robot control system is designed based on hierarchical and modularization strategy,which includes upper monitoring system and lower control system.The prototype of robot including mechanical system and control system is developed based on the former research.Then several experiments are designed for the adhesion ability,steering capability,adaptive capacity and obstacle crossing ability of the robot.The experimental results indicate the validity and rationality of the robot design and theory analysis.