Abstract: In view of the lower paralysis patients, a new type of 3-DOF parallel lower limb exoskeleton mechanism is designed as the foundation for research, the forward and inverse position solution of the mechanism are analyzed with product of exponentials (POE) formulation, in the meanwhile, the Jacobian matrix and motion singularity of mechanism are also analyzed. Taking the maximum workspace as the objective function, the chief factors influencing the workspace of the parallel mechanism such as the workspace restriction of the length of linkage, the angle of motion pair and the human body’s joint angle have been taken into account. The boundary of workspace is determined with the help of boundary search method, and the area of workspace is calculated. The influence of various parameters of the mechanism on the workspace is analyzed. On the basis of kinematics analysis, in order to satisfy the demand of hip’s angle and knee’s angle range of motion of normal human walking, to improve the mechanism kinematic performance as the goal, optimize the value of structural parameters. Preliminary analysis shows that the kinematical performance can been improved with optimizing the value of the structural parameters. The mechanism can be used to lower limb paralysis patients in rehabilitation training. The study paves the way for the design and analysis of the parallel mechanisms.

Key words: forward and inverse position solution, lower limb exoskeleton, products of exponentials, workspace