Study On Wheel Led Hybrid Wall Climbing Robot And Its Key Technology

Wall-climbing robot is an important branch of mobile robot, which can move on vertical surfaces and work by carrying kinds of tools. It has been studied and applyed in the field such as petrifaction, nuclear power station, ship, cleaning for outer wall surfaces of high structures, and so on. In resent years, wall climbing robot is studied for special tasks such as rescue, inspection, surveillance and reconnaissance. It has important theory research significance and has wide application prospect. In this paper, a prototype of wheel-leg hybrid mobile robot that can move on both ground and wall surfaces is presented, which have the ability of transmitting between graound and wall surface. Key technology including dynamics of robot on wall surface, local obstacle-avoiding trajectory planning, motion plan for robot's legged motion and smooth motion control of robot in legged mode is studied in the paper.Motion space is a key item for the robot's application which can improve the movement space. Base on the advantages of wheeled wall climbing robot and legged robot, a prototype of wheel-leg hybrid mobile robot is designed. The designed sucker constrcted of inside and outside seal skirt and the designed lifting mechanism for suckers meets the wheeled mode and legged mode respectively. They realize the switching between the two motion modes. Motion in wheeled mode has high moving speed, and motion in legged mode can realize transition between ground and wall surface and climb over obstacles on wall. Safe adhesion requirement is analyzed for the robot in the two modes respectively, and the needed adhesion pressure is obtained. Then, kinematics analysis is conducted for the robot in the two modes respectively, which offer basis for the robot's motion control.For motion of the robot in wheeled mode on vertical surface, dynamics analysis of the four-wheel driving wall-climbing robot in skid-steering mode is important for the structure design and motion control. First, motion state and constraint of robot on wall surface is analyzed; distribution of supporting forces on driving wheels, laterial friction force between driving wheel and wall surface, and friction force on sealskirt of suckers are analyzed, then dynamic model of the robot is constructed based on the Newton-Euler method. A safty factor of driving torques Dissertation for the Doctoral Degree of Harbin Institute of Technology is established to denote the safe degree of driving torques. And influence of distribution of driving wheels and rigidity of sealskirt on driving torque is analyzed.Obstacle avoidance is important in the motion control of robot. Robot's obstcal avoiding motion plan on plane is studied. Based on non-contact impedance force, distance between obstacle and robot is transmited into a force on robot. By establishing an impedance mode between the robot and environment, a robot motion plan strategy is proposed in the aim of tracking telecontrol speed and obstacles avoidance. The introduction of velocity item improves the smooth of robot's motion. For the robot's motion in legged mode on wall surface, kinematics of the centre of mass is analyzed, and ZMP is introduced into the stability analysis of the robot. Distance between ZMP and edge of stick sucker is defined as stability margin. Then a motion plan strategy based on genetic algorithm for robot's legged motion is proposed, which imprve the stability of robot's motion in legged mode.Legged motion mode of the robot is realized by alternate adsorption of the two suckers, which can realize transition motion between ground and wall and stepping over gap and boss. In this mode, landing and lift of sucker is the key motion to realize smooth motion. In the paper, a location and orientation control strategy is introduced, by detectting the contact force between the sucker and surface. The smooth trasimiting of sucker between free space and constructed space is realized.The strategy realizes robot's reliable movement in legged mode under the condition of the position error and attitude angle error, and avoids the failure of robot's legged motion under the error of inclination in the transition movement. Finally, control system is designed based on hierarchical and modularization strategy, which includes upper computer and controller on the robot. The upper computer realizes message interchange between hunman and robot; the controller is composed of two levels, including main controller which gather sensor data and execute tasks, and motor servo controller which control the motors. Then the experiment about the adhesiong ability and robot's movement in wheeled mode and legged mode is implemented, the results validate the motion ability of the robot. Experiment results indicate the correctness and effectiveness of the theory analysis.