Design Of A Two-wheel And Self-balance Robot With A Variable Structure

Wheeled robots are featured as fast and stable driving on a flat road,gaining more flexibility and high movement efficiency.Rotation can be achieved at any radius by wheel,but lack the ability of crossing obstacles and traversing rough terrains.When different shaped wheels are used,different movement modes can be achieved,and thus enhance the adaptability to different environments.However,compared to other movement modes,such as walking and jumping,special-shaped wheels'ability of overcoming the obstacles are often limited by the size of the robot.Among the existing mobile modes,jumping is the most efficient way to overcome the obstacles.In this paper,a two-wheel and self-balance robot with a variable structure is designed in a small scale.The robot is designed as a research topic for the monitor and search missions in extreme environment.To improve the ability of crossing obstacles,jumping mode is involved and then a wheeled-hopping and self-balance robot is designed.Two aspects are involved in the process of designing the wheeled-hopping robot:the realization of bouncing motion and the control system of the robot.The main structure of the hopping robot consists of two parts:the storage-release energy mechanism with the characteristic of quick return and the other one is the bounce actuator.The former is used for the energy storage and instant release so that the initial acceleration and velocity for hopping can be obtained.The actuator is used to interact with the ground directly.In this paper,the hopping principle will be studied and analyzed from the perspective of bionics,the structure schemes will be made and their feasibility will be compared based on the theoretical and kinematic simulation.The specific schemes are as follows:(1)The principle of the structure design is that the center of gravity of the robot is located below the wheel axle,so as to realize the balance by its own structure.The leg and the wheel are combined to realize the hopping motion of the wheeled robot;(2)The whole structure is designed as "inverted pendulum",relying on the control algorithm to keep balance.Connected in parallel,the legs and wheels are designed.The gear train and cable is designed to switch the modes between moving by wheel and jumping.In this scheme,a novel screw nut mechanism and four-bar linkage are designed to realize the bouncing motion;(3)The whole structure is designed as "inverted pendulum",relying on the control algorithm to keep balance.Connected in series,the wheels and legs are designed here.The gear train with a missing gear is designed to compress and release the torsional spring for hopping.Through the comparison of the simulation results and the theoretical analysis results of the three schemes,the third scheme was selected and its dynamics model was created.The control system and prototype were made based on this scheme.And the experiment was carried out of which the results show that the obstacle that the robot can cross is about 60%of its own height.The experimental results indicate that the wheeled robots with the capacity of jumping is an effective way to enhance their ability of overcoming the barrier.