On The Mechanism Performance Analysis And Motion Control Of The Two Types Of Parallel Manipulators

The planar two degree-of-freedom parallel manipulators with redundant actuations and wire-driven parallel manipulators, which have abroad applications and valuable exploitations, play important roles in the family of parallel manipulators. Workspace, singularity, stiffness, optimal force distribution, dynamic modeling and motion control of the two types of parallel manipulators are studied in this paper, and the research results can found theoretical and technical basis for performance improvement and engineering application of the two manipulators. The main contents can be described as follows.1. The functional relationship between the structural parameters of the planar two degree-of-freedom parallel manipulators with and without redundant actuations and the configurations of their workspaces is established. And the workspace spectrograms for the two parallel manipulators are drawn respectively. The strength and weakness of the two types of workspaces are compared, which provide a systematic basis of reference for the design of the two parallel manipulators.The singularities of the planar two degree-of-freedom parallel manipulators with and without redundant actuations are discussed respectively. Further the analytic expressions of singular loci are derived and the spectrograms of singular loci are drawn in terms of some dimensionless parameters. By contrastive analysis of the spectrograms, the availability of actuation redundancy on eliminating singularities of the parallel manipulators is shown. The research provides a valuable reference for the singularity-free trajectory planning.2. The optimization of comprehensive performance of a planar two degree-of-freedom parallel manipulator with redundant actuation is investigated. Based on the kinematics model of the manipulator, its Jacobian matrix and optimal topologies are given. The influences of structural parameters of the manipulator on its workspace and singularity are discussed. A comprehensive performance criterion is proposed to evaluate kinematics accuracy, force transmissibility, structural stiffness and workspace utilization rate. An optimization model with the proposed criterion as the objective function and taskspace and nonsingular configuration as the constrains is constructed, and an adaptive genetic algorithm is utilized to obtain the optimal solution.3. The workspaces of incompletely restrained, completely restrained and redundant restrained wire-driven parallel manipulators are investigated. Existence conditions of workspaces of the three types of wire-driven parallel manipulators are given and proved by a theorem and three corollaries. According to the theorem and corollaries, a uniform solution strategy is proposed to determine the workspaces of the three types of wire-driven parallel manipulators. The workspaces of three typical wire-driven parallel manipulators are obtained and compared using the proposed strategy.4. A stiffness model of wire-driven parallel manipulators is established, which depends on the elastic deformation of joints and wire tension. And a mathematical formulation of stiffness matix is followed. Numerical simulations demonstrate the effect of configuration parameters and wire tension on stiffness of wire-driven parallel manipulators. The results lay theoretical foundations for stiffness control to wire-driven parallel manipulators.5. The dynamic control of two wire-driven parallel manipulators which are employed as a flexible support system for the aircraft wind tunnel and a cable-cabin coarse tuning system of the large radio telescope, is presented. Firstly, the dynamic models of the two wire-driven parallel manipulators are developed respectively using Newton-Euler's method.For a six degree-of-freedom wire-driven parallel manipulator with redundant actuations for low speed wind tunnels, a modified Proportional-Differential control strategy with feedforward compensation in the wire length coordinates is developed based on stiffness enhancement. And an optimal tension distribution is implemented for the enhancement of stiffness at lift, along-wind and pitching directions, in order that the problem of a high dynamic positioning errors of the aircraft model can be resolved.A wire-driven parallel manipulator which has been found application in the large radio telescope is utilized to alter the pose of the cabin. Considering the constraints on the cable strength and the loads of the motors, the optimum tensions are obtained according to minimizing the norm of cable tensions. The nonlinear state feedback compensation is introduced to a modified PD forward controller in the cable length coordinates. And a disturbance observer is used to estimate the disturbance exerting on the motors to suppress the disturbance effect.