Research On The Theory Of The Parallel Manipulators With Equivalent Compound Joints

Compared with series mechanism,the parallel manipulators(PMs)have several advantages,such as high specific stiffness,small accumulative error and large capacity of load bearing.Recently various parallel manipulators(PMs)have been applied in fields of parallel machine tool,micro–Nano operation of bio-medicine,force/torque sensor,motion simulator and so on.Based on digital topology graph,12 novel PMs with equivalent compound joints are synthesized,and their degrees of freedom are calculated.The multifingered hands have many advantages,like highly flexibility,easily to adjust the position and orientation,grasping diversification compared with conventional end effector.Combined with practical application requirements,three fingers are arranged on moving platform of the parallel manipulator with equivalent compound joints.Based on the different axial arrangement of the rotating pair in the equivalent compound jounts,the structural characteristics of two kinds of compound driving branches are analyzed respectively.According to the structural characteristics of the compound driving branches,the inverse displacement of the compound driving branches and the forward displacement of the fingers are derived by the vector method.The fixed orientationworkspace of the 5-DOF PM is cnscructed by using the CAD variation geometry.Based on the constrained equations of this class of PMs,the coupling formula of moving platform is derived,which provide a reference for prototype design,and structure optimization of the PMs.According to the motion among the components,the relationship between the driving branches and the moving platform is discovered by using the vector method.The constraints of this class of PMs are mainly represented by constrained forces/torques.Based on the arrangement of joints in the sub chains,the constrained force/torques are determined.A novel method for establishing Jabobian of this class of PMs is proposed based on the characteristic of the constrained force/torques.The Hessian matrix of this class of PMs is derived,and the kinematics model of this class of PMs is built.Finally,the singularity of the mechanism was also analyzed based on Jacobian matrix,and then the singular conditions were obtained.Based on the principle of virtual work and Newton Euler Equation,the unified static and dynamic models of this class of PMs with equivalent compound joints are established.The relationship between the driving force and the load is discovered.The static and dynamic models of the parallel mechanism are established and verified based on CAD virtual prototyping technology and compiled program.The mechanical models of components in the PMs with equivalent compound joint are established.The compression deformation and bending deformation of the components in the mechanism are analysised.Consider the deformation of the beam in the compound drive branch,the general stiffness matrix is built,and the center of moving platform deformation is calculated.The finite element simulation models of this class of PMs are built.The error between the theoretical solution and the simulation is analyzed.According to the moving relationship between the target object and the fingers,coordinated kinematics of the fingers and the hybrid hands with equivalent compound joints is systematically analyzed in the process of the grasp and manipulation.The criterion for the closeness of force of target body is given.Utilizing matrix theory,the formula for calculating contact force of fingers is deduced.The maximum frictional force is taken as boundary condition,and the contact force of fingers is optimized.It provides a reference for robot research and application.A prototype of the 4-DOF hybrid hand with equivalent compound joint is built up based on the adjustable active legs.This prototype has been applied for kinematical experimentation successfully.