Configuration Design And Singularity Analysis Of Parallel Leg Mechanism With Kinematic Bifurcation

In this paper,the parallel leg mechanism with bifurcation function is designed and studied.According to different working environment and changing task requirements,a kind of parallel leg mechanism with multi degree of freedom mode of 3R3 T,3R2T,3R1 T and 2R1 T is designed.The bifurcated parallel leg combines the characteristics of large bearing capacity,small cumulative error,good dynamic performance,large stiffness of the parallel mechanism with the characteristics of multi-mode motion of the reconfigurable mechanism,which not only improves the performance of the walking robot,but also expands the application of the walking robot.In this paper,the linear combination of five moving spirals is used to generate the moving spirals of various branches.The generated helix is combined to form a branch chain with 3,4 and 5 rotating pairs.The RRS branch is chosen as the branch of the bifurcation mechanism.The final configuration of the parallel leg is 3-(P)RRS by introducing the closed chain with 1R and 1R1 T modes of freedom.Then,the constraint mode of the hybrid branch chain is analyzed,and the constraint vector mode with 3R2 T degree of freedom and the unconstrained mode with 3R3 T degree of freedom are obtained.Secondly,the two modes of the hybrid branch chain are combined to obtain the parallel leg with four degrees of freedom,namely 3R3 T,3R2T,3R1 T and 2R1 T.Finally,we choose the appropriate branch chain drive and prove the rationality of the drive selection.Then,two kinds of parallel legs,3R3 T and 2R1 T,are selected from the four degrees of freedom of 3R3 T,3R2T,3R1 T and 2R1T: the inverse kinematics analysis of 3R3 T mode;the forward and inverse kinematics analysis of 2R1 T mode.The position parameters of 2R1 T parallel leg are simulated to verify the correctness of the forward and inverse solutions.The velocity Jacobian matrix of 3R3 T mode and the total Jacobian matrix of 2R1 T mode are calculated.The singular configuration of the 3R3 T mode of the bifurcated parallel leg is calculated and verified.By using the boundary search method of numerical method,the fixed attitude workspace of 3R3 T mode and 2R1 T mode is solved.The gait of the robot is planned,and the walking simulation is carried out with appropriate gait.The walking simulation is carried out with the walking mode of first out the left front leg,then out the right front leg,then out the left rear leg,and finally out the right rear leg(acbd type gait planning).Through the image,the specific process of parallel leg mode switching is presented.The 2R1 T mode and 3R3 T mode of parallel leg are simulated,and the displacement amplitude curve and displacement velocity curve of four parallel leg feet in two walking modes are drawn.