Kinematics Analysis Of A Novel Serial-Parallel Hybrid Leg Structure Applied On Walking Robot

The walking robot has the advantages of good stability,flexible motion and strong adaptability to complex terrain.It can be applied to many fields such as scientific investigation,national defense,space exploration,etc.It is one of the hot topic in the field of robot research.The performance of the robot's leg mechanism directly affects the motion performance of the robot.At present,the leg mechanism of the walking robot mostly adopts serial mechanism and parallel mechanism,and relatively few studies on the hybrid mechanism.The serial leg mechanism has the characteristics of large working space,simple structure and easy control,but its driving and joint are often integrated,resulting in large motion inertia,relatively small rigidity and low carrying capacity;The parallel mechanism has the characteristics of strong carrying capacity,compact structure,small weight/load ratio,but its working space is relatively small;The hybrid mechanism integrates the advantages of the serial mechanism and the parallel mechanism.The rational design of the hybrid mechanism enables the leg mechanism to have better carrying capacity and a larger working space.A novel 4-DOF serialparallel hybrid robotic leg mechanism was presented.The mechanism consists of a main branch and four drive branches.The main branch is composed of two hook hinges in series;the four driving branches are connected in parallel in groups,and each group corresponds to a hook hinge in the main branch.The two-degree-of-freedom rotational motion of the corresponding hook hinge is driven by driving the movement of the prismatic pair on the drive branch.The new leg mechanism realizes the separation of the driving space from the joint space.The drive is placed on the back of the machine to reduce the inertia load during leg movement and improve the mobility of leg movement.The main contents of this paper are as follows:1.A novel serial-parallel hybrid robotic leg mechanism was proposed,and the rationality of freedom and driving input selection was analyzed based on the screw theory.The kinematic screw system of leg mechanism was established,and the structural constraint screw system of leg mechanism was obtained by the reciprocity of screw theory.The degree of freedom of the hybrid leg mechanism was determined by analyzing constraint screw system of the leg mechanism.Furthermore,based on the screw theory,the rationality of the drive input combination was verified and the drive mapping relationship between the main branch and the drive branch was obtained.2.Based on the D-H method,the linkage coordinate system of the main branch and the drive branch coordinate system were established.The kinematics forward and inverse solution model of the novel hybrid leg mechanism were obtained by combining the homogeneous coordinate transformation and the rod length invariance principle.The kinematic mapping relationship from joint space to drive space was obtained.The specific examples of six sets of foot endpoints are given,and the forward and reverse solution models were verified by MATLAB software.3.The velocity Jacobian matrix of the main branch was obtained by differential transformation.Using the Gosselin singular analysis method,the velocity Jacobian matrix of the driving branch was obtained.According to the speed Jacques matrix,the singular configuration of the mechanism was analyzed.Constraint model of workspace of hybrid leg mechanism was established.Based on the constraint model,the boundary search method and MATLAB software were used to draw the working space of the foot endpoint.The working space of the leg was similar to the ball crown.4.Based on the hybrid leg model,the ADAMS virtual prototype model was established,and the related parameters such as the motion sub-constraint and quality attributes of the leg mechanism were set.Based on ADAMS software and MATLAB software,a motion co-simulation platform was established.The typical motion trajectory of the foot endpoint was simulated and verified on the platform.The results verified the correctness of the theoretical analysis and provided a basis for the selection of the driving parameters.This paper lays a foundation for further research on dynamics research,system control research,prototype trial production of the serial-parallel hybrid robotic leg mechanism.At the same time,it enriches the kinematics theory of hybrid institutions.