Design And Analysis Of A Novel Cable-Driven Parallel Mechanism For Ankle Rehabilitation

In this paper, a novel cable-driven parallel mechanism based on the motion characteristics of human ankle joint is proposed for ankle rehabilitation. Because of the novel mechanical design of the equivalent spherical joint and platform, the mechanism centre of rotations can easily match the ankle axes of rotations, which is an advantage over some existing rehabilitation robots. This study is the first systemic to apply cable-driven parallel mechanism to ankle rehabilitation field, Which widens the application scope of cable-driven technology. The main contents are as follows:Firstly, we discussed the movement function, ingury and rehabilitation training of ankle by the related knowledge of anatomy, clinical medicine, rehabilitation medicine and so on. The author puts forward the basic design principles of the novel cable-driven parallel mechanism and complete the mechanism design in theory. On the basis of the principles of mechanism design, the overall structural design of is completed. Then, the author also introduces the specific design of each part and analyzes the degree of freedom of the cable-driven mechanism for ankle rehabilitation, which verifies its kinematic performance preliminarily.Then, the kinematics of the cable-driven mechanism for ankle rehabilitation is analyzed, including:closed-vector-circle method is used to establish the inverse kinematic model of the mechanism; speed and acceleration inverse solution of the mechanism kinematics are deduced; The analytic solution and numeric solution of the forward kinematics solutions are established by the Rodrigues parameters method and Newton-Raphson method; On the basis of calculating examples, the author verifies the correctness of the forward and inverse kinematic models and draws the change curves of cable length, speed and acceleration when moving platform rotates around the fixed axis, which lays theoretical foundation for the subsequent analysis.Next, the statics of the cable-driven mechanism for ankle rehabilitation is analyzed. The forces controllable and adjustable workspace are solved separately, the scope of whose working spaces are drawn by MATLAB. The author analyzes and optimizes the distribution principle and algorithm of tension brought by the driving cable. And according to the feature of redundancy, the author redefines the minimum solution, the highest solution and the optimal solution of the driving cable’s tension. At the same time, the algorithm of tension distribution is proved correctly by the simulation research. The dynamic models of the mechanism moving platform, the drive and the whole system are established by the methods of Newton-Euler. The author evaluates the dexterity and singularity of the mechanism, deduces the stiffness matrix of the mechanism, calculates the stiffness value and provides evaluation index of the stiffness matrix, based on the basic definition of stiffness.Last, the author builds the virtual prototype modeling of the cable-driven mechanism for ankle rehabilitation, makes a research of kinematics simulation and completes the rehabilitation exercise trajectory planning and simulation of the mechanism by Adams software. The results of simulation further verifies the motion ability of the cable-driven mechanism for ankle rehabilitation, meeting the design requirements.