Research On Kinematic Performance Of Wheel-legged Robot Based On RPR/RRPR Spherical Parallel Mechanism

Wheel-legged robot is a kind of mobile robot,which is widely used in rescue and detection missions because of its excellent obstacle negotiating ability and higher mobile efficiency.Because the lower mobility spherical parallel mechanism with two limbs has higher flexibility,stronger bearing capacity and larger motion space,the RPR/RRPR spherical parallel mechanism is applied to the leg structure of the wheel-legged robot,which can improve the flexibility,bearing capacity and obstacle negotiating ability of the wheel-legged robot.This paper mainly studies the kinematic performance of the wheel-legged robot.Firstly,the whole mechanism of the wheel-legged robot is designed,including the leg structure,the wheel structure and the transmission system of the wheel-legged robot.The RPR/RRPR spherical parallel mechanism is used as the leg structure of the wheel-legged robot.Four identical legs are distributed on both sides of the robot,and the movements of the legs do not interfere with each other.The wheel is mounted at the spherical center of the RPR/RRPR spherical parallel mechanism,the wheel is separated from the leg,and the movement does not interfere with each other.The transmission system of the wheel-legged robot adopts synchronou belt and synchronous wheel structure.The main function of the transmission system is to realize the wheel-legged switching process and wheeled motion of the wheel-legged robot.Secondly,based on helical theory,the mathematical model of the leg RPR/RRPR spherical parallel mechanism is established.Kinematic screw system and the inverse screw system of the mechanism are obtained.The common constraint of the RPR/RRPR spherical parallel mechanism is also obtained.The forward and inverse kinematics solution of the mechanism are obtained using vector method.The correctness of the kinematics equations of the mechanism is verified by MATLAB and SolidWorks software.The relationship between the workspace of the RPR/RRPR spherical parallel mechanism and the angle of the rotating rod and the fixed rod is studied.Then,takeing horse as an example three typical gaits of quadruped animal,such as slow gait,trot gait and gallop gait,are analyzed.According to the working environment of the wheel-legged robot,the slow gait and trot gait are used as the moving gait in the wheel-legged robot leg mode.The stability of wheel-legged robot under the slow gait is analyzed by means of centroid projection method.The angle?of each side of three prism is formed by gravity vector,centroid and supporting point as stability criterion.The bigger?wheeled robot is,the more stable it is under this gait.The stability of wheel-legged robot in trot gait is analyzed by using zero-moment point method.The stability of wheel-legged robot in trot gait is evaluated by the||x_ZMP||of zero torque point.The smaller the||x_ZMP|,the more stable the wheeled robot is.The maximum uncapsized angle of the wheel-legged robot moving on the slope is obtained.Finally,the virtual prototype of the wheel-legged robot is established using SolidWorks software.The motion process of the wheel-legged robot under slow gait and the trot gait is designed.The gait's length and height of the wheel-legged robot are also analyzed.The variation of mass center of wheel-legged robot in slow gait and trot gait is also obtained.Two kinds of obstacle types,i.e.gully and convex platform,are designed.The motion process of wheel-legged robot over these two obstacles has also been designed.The variations of the center of mass and the torque of servo drive motor have also been analyzed.