Research On Kinematics,Dynamics And Active Vibration Control Of Six-DOF Parallel Robots

Parallel robots have the advantages of high rigidity,low inertia,high speed and high precision.Their applications cover not only industry but also field and service robots.In terms of high performances,their analysis is far from being complete.This dissertation focuses on the theory and application of six-DOF parallel robots,involving modeling and algorithm of kinematics and dynamics,optimal design of mechanisms and structures,and active vibration control strategies.For the forward kinematics of 6-DOF parallel robots,the most efficient numerical algorithm is proposed.The convergence and singularity are then discussed.The algorithm is effective for both full and redundant actuation.The new algorithm improves the computational efficiency by 64 times compared to the traditional Newton's method.The representation and determination of the singularity-free joint space and workspace of 6-DOF parallel robots are studied.It is proposed to calculate the maximal singularityfree joint space firstly and then automatically obtain the maximal singularity-free workspace.Compared with the traditional algorithm,the computational efficiency is improved by 51 times.A computationally efficient inverse dynamics of 6-DOF parallel robots is researched.A unit dual quaternion is selected as the generalized coordinates of the system.The equations of motion are established using the principle of virtual power.For the 6-UPS and 6-PUS parallel robots,the new approach reduces the amount of calculations by 43.45% and 38.45% respectively,compared to the conventional dynamics.The kinematics optimal design of a six-axis vibration isolator via the Stewart platform is studied.A dimensionally homogeneous Jacobian matrix formulation is proposed to avoid the inconsistency of the units of rotation and translation.The local kinematic isotropy is set as the performance index.The genetic algorithm is then used to obtain the optimal configuration.The dynamic isotropic design and active decentralized control of a six-axis vibration isolator via Stewart platform are studied.The analytic conditions for the complete dynamic isotropy of the isolator in the free-floating state is obtained for the first time.The inherent relation between the dynamic isotropy and kinematic isotropy is revealed.A decentralized controller is designed for an isolator of dynamic isotropy.The closed-loop system is isotropic and has uniform vibration isolation performance in all directions.The dynamic modeling and active vibration control of the flexible Stewart platform are studied.Using the pseudo-rigid-body model and the principle of virtual power,the explicit linearized dynamic equations with sufficient accuracy and simplicity are deduced.A decoupled control algorithm is then synthesized.The position feedback compensates for the parasitic bending and torsional stiffness of the flexible joints.The force feedback realizes the vibration control in modal space.The proportional and integral gains respectively regulate the corner frequency and active damping of the six vibration modes.This work provides a new theoretical foundation for improving the performance of parallel robots.It can be used to effectively guide the design,motion analysis and execution of high-speed and high-precision parallel robots.Finally,the concluding remarks and further research directions are provided.