| Compared with serial manipulators, parallel mechanisms have characteristics such as high precision, without errors accumulation, high bearing rigidity etc, which attracted the attentions of international researchers. However, most researches on the parallel mechanism focu on the classical mechanism which represented by the Stewart platform. With the industry development, variety of parallel mechanisms with its own unique performances have been emerging. The 3-PRPS parallel manipulator is one of them. It has the capability of pure rotation and intuitive prediction of the moving platform movement, simple kinematic character etc. Application prospects of the mechanism are extensive, as high-precision detecting robots. However, when the mechanism is applied to industry, the applicable scope and working performance are limited immensely because of lacking of theoretical support on the structure optimization design, definitions of end-effector's work scope, reasonable selections of mechanism parameters, adjustments of controller parameters etc. Although in recent years its theoretical research obtains certain development, there are also some challenge issues on the kinematics, workspace etc, such as that kinematic model has not been perfected, that lacking of effective method to solve workspace, that the mechanism's motion changes which the key parameter affects are indefinite etc. Consequently, characteristic studies of the 3-PRPS parallel manipulator have an important theoretic value and practical significance.Based on the aforesaid opinion, this paper analyzes and discusses several problems of the 3-PRPS parallel manipulator on the characteristics of kinematics, workspace, the key parameter and controller design etc. The main work includes:Firstly, this paper builds a relatively perfect kinematics model of the 3-PRPS parallel manipulator, then get an analytical expression is obtained which could describe the reverse kinematic relationship uniformly. Therefore, solutions of the inverse kinematics could also be acquired. Based on the practical instance, position inverse solution is calculated and compared. Kinematic characteristics are then summarized.Secondly, this paper presents several important factors that affect the workspace of 3-PRPS parallel manipulator. According to its characteristic, geometry method is used to solve the work space with Matlab. Under given parameters, workspace is obtained which forms with a shape of a approximate hexagonal pole. Workspace is one of important indexes which used to evaluate the performance of parallel mechanisms. Solutions of the workspace intuitively reveal these characteristics of the 3-PRPS parallel manipulator.Thirdly, the ratio K (the ratio of circumradius of the fixed platform and apothem of the moving platform) is a key parameter of the 3-PRPS parallel manipulator. In order to thoroughly analyze relationships between the ratio K and the manipulator's motion, ADAMS software is applied to build models, and carry out simulation in the same condition. Influence of the ratio K on the manipulator's motion is analyzed. There is a important practical meaning for the optimization design and the control system to understand the role of ratio K in the 3-PRPS parallel manipulator properly.Fourthly, based on these theories about the kinematics, workspace, analysis of mechanism parameters, this paper presents the controller design program of the 3-PRPS parallel manipulator. Design the structure of actuating links is also tried.The research builds a theoretical foundation for optimization design of structural parameters, controller parameter adjustments and industrial applications etc. In addition, the discussion and analysis of ratio K could apply practicably. Some related research methods will provide important references for the study of same type of high precision parallel mechanism. |
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