The Singularity Research Of 3-CRP_4RRR Parallel Mechanism Based On Screw Theory

The parallel mechanism is composed of static platform, moving platform and two or more kinematic chain between the two platforms. It has many advantages of more degrees of freedom, stable structure, high carrying capacity, high movement accuracy. The singularity of parallel mechanism affects the mechanism’s performance, such as range of motion, work space, force, control, etc. It is an important part of theory of parallel mechanism research and the theoretical basis to understand new institutions.This paper researches a new kind of 3-CRP4 RRR parallel mechanism by using screw theory to analyze the degrees of freedom, the singularity and makes the related researches for the parallelogram kinematic chain in the branched chain. Specific content is as follows:1. This paper generally introduces the internal and overseas development and application for the 6-DOF parallel mechanism, theoretical contents and research methods,the study of singularity, which lead to the content of the research for new institutions below.2.The basic principle of the screw theory is introduced in this paper. According to the structure characteristics of 3-CRP4 RRR parallel mechanism, this paper reasonably set up the branches, fixed and dynamic coordinate system. On this basis, the improved formula of freedom is used to analyze the mechanism’s degrees of freedom. Mechanism’s branch of motion screw is established in the same coordinate system, to be prepared for the analysis of singularity.3.This paper briefly introduces the fundamental theories on singularity of parallel mechanisms. And the singularity of the 3-CRP4 RRR parallel mechanism based on the constraint screw theory is analyzed followed, which include kinematics singularity and constraint singularity when only translational motion. This paper has given the various states when in kinematics singularity, and proposed a solution to eliminate the constraint singularity by changing the position of the driver.4.Movement and characteristic of the parallelogram kinematic chain are analyzed.This paper summarizes two kinds of special singularity of the new mechanism, and analyzes the movements under special positions. According to the previous analysis, this article summarizes the necessary conditions only translation output. It will be a reference for the further researches of the 3-CRP4 RRR parallel mechanism.