Parasitic Motion Analysis and Architecture Design of (PP)S Parallel Mechanisms
|School||Zhejiang University of Technology|
|Course||Mechanical and Electronic Engineering|
|Keywords||[PP]S Parallel Manipulator Parasitic Motion Screw Theory Singular Configuration Workspace|
Compared with the general 6-DOF (degrees of freedom) parallel mechanism, lower-mobility parallel mechanisms have advantages of simple structure, low cost in design, manufacturing and control. The [PP]S parallel mechanism (PM) is an important category of lower-mobility parallel mechanisms and has received extensive attention, which can undergo one translational degree of freedom (DOF) and two rotational DOFs. Thus, the [PP]S PM has great potential in practical application.This paper focuses on the parasitic motion of [PP]S parallel mechanisms and aims to reveal the inherent link between the geometrical structural parameters with the parasitic motion. Based on the structural condition, the new [PP]S parallel mechanisms without parasitic motion can be constructed. And then kinematic analysis of 3-PRRU PM are proposed, the prototype is constructed. The main contributions are as follows.Based on the relative position relationship between three limb planes(LPs) and three centers of spherical hinges, the family of [PP]S parallel mechanism is classified. Then analyze its parasitic motion by using the kinematics method respectively and compare with each other.The inherent link between the geometrical structural parameters and the parasitic motion is established, and the necessary structural parameters for a general 3-PRS parallel mechanism without parasitic motion are proved. The sufficient and necessary structural condition is also applicable to other [PP]S parallel mechanisms. Based on the structural condition, evolve the multiple family of [PP]S parallel mechanisms and its topological mechanisms.The degree of freedom of a 3-PRRU parallel mechanism is analyzed by using screw theory, and its inactive pairs and parasitic motion is discussed. Take advantage of structural character of a 3-PRRU parallel mechanism without parasitic motion, forward and inverse position analysis is simplified, and the tool’s position formulation also be listed. Then build the velocity jacobi of the 3-PRRU parallel mechanism.Based on velocity jacobi, analyze the multiple singularities and actuation failure of 3-PRRU parallel mechanism. And then propose its capability of orientation which helpful in gaining workspace of tool extremity. Dexterity in different configuration also can be gained. Through observe dexterity performance map, bad kinematics performance can be avoided in actual motion, which can raise mechanism reliability.The achievements stated in this thesis lays a solid foundation for the development of all kind of [PP]S PMs with no parasitic motion.