Research On Design Method Of 3-PRS Parallel Mechanism

The 3-PRS parallel mechanism is a three degrees of freedom spatial mechanism, whose end effector can implement one translational and two ratational mixed motions. Due to fewer number of the limbs, symmetrical architecture, more easily arrangement of the actuators, achievable three dimensional manipulation and a sub-structure candidate for the dipolar manipulator, the 3-PRS parallel mechanism is a comparatively ideal choosable mechanism. This paper outspreads researches surround 3-PRS parallel mechanism's inverse kinematics, workspace and mechanism synthesis for the purpose of anatomising its design mechanism and providing theoretical basis for invention of three coordinates parallel dynamical head which owns Chinese self-determination intellectual property rights.Firstly, the kinematic model of 3-PRS parallel mechanism is established using the closed-loop vectors method. The inverse position solution and velocity mapping model can be obtained. On base of this, the engen of the parasitic motions and the relationship between the parasitic motions and mechanism parameters are analyzed. The results obtained reveal that, with the increase of the radium of the moving platform, the extents of parasitic motions augment evidently. Therefore the influence of the parasitic motions shouldn't be neglectable.Secondly, the paper presents the concrete definition of the 3-PRS parallel mechanism's workspace aiming at its self structure characteristics on the base of the inverse kinematic analysis. Then the constraining conditions according as some restricted factors such as actuated journey, gemel angle and link size interposition, etc. are confirmed. 3-PRS parallel mechanism's workspace is searched using the terminal verge search arithmetics. The sensitivity analysis of the volume of the workspace subject to some key structure parameters is derived, which lays the foundation of the kinematical design.Finally, the dimensionless Jacobian matrix of the 3-PRS parallel mechanism is deduced, whose correlative algebra characteristics is selected as the macrocosm performance evaluating index. This index considers both the average level of the mechanism's kinematic performance during the entire workspace and the fluctuate stability of the performance simultaneously. The target function is confirmed using this index. The 3-PRS parallel mechanism is investigated by means of monotonic analysis, leading to a set of appropriate constraints. Consequently, the optimal kinematic design of the mechanism is implemented by solving a nonlinear algebra equation. An illustrative example is used to validate the dimensional synthesis method proposed.