A Study On Analysis And Synthesis Of Adjustable Mechanisms

Mufti-axis open-loop robots are under-utilized and the cost of maintenance is relatively high, when they're used in limited similar tasks. On the other hand, conventional automation mechanisms are comparatively simpler in structure, but lack in flexibility. Even though the adjustment of the task is very little, the mechanisms have to be redesigned. In adjustable mechanisms, the dimensions and/or the positions of one or several particular links can be adjusted so that the mechanisms can generate different tasks. They have the advantages of above two while overcome their disadvantages.In the automatic production, a machine is required to perform comparatively simple tasks respectively and quickly in case there is intelligence received to select one or the other task. Compared with mufti-purpose robot manipulators with multiple actuators, single purpose, single input purely mechanical devices are more reliable, more accurate, much easier to manufacture and maintain, and more economical. Mechanisms with adjustable links can be used as such devices to perform highly respectively simple sets of tasks. These characteristics make adjustable mechanisms have very vast potential applications. Guidance synthesis, displacement analysis, path synthesis, dynamic analysis of spatial RRSS four-bar, spherical five-bar mechanisms and parallel machine tools are studied in this thesis.A method of rigid-body guidance synthesis for adjustable spatial RRSS mechanism is presented, and the corresponding design equations are derived by divided links and tasks. Particularly, the design equations for R-R link are set by using co-plane and inversion theory. In this way the complication can be simplified. The mechanisms can achieve multiple alternative tasks by adjusting some structure parameters. Then relation between the number of tasks and the maximum number of prescribed precision positions are given. The sets of nonlinear synthesis equations were solved by using chaos optimization algorithm, and a numerical example is given to illustrate it.Based on kinematics model of spherical five-bar mechanism, the analytical solutions of direct kinematics and inverse kinematics are deduced, the working and assembly modes of the mechanism are analyzed, and the mechanism's Jacobian matrix is derived. The singularity conditions of spherical five-bar mechanism are discussed according to the Jacobian matrix. Then the coupler point kinematics of spherical five-bar mechanism is analyzed. By using the computer simulation method, the coupler curves of spherical five-bar mechanism with double crank and some laws of the curves changing with the mechanism parameters are investigated respectively.Using Pro/E software, the virtual prototype of the 4-Dof 2-RPS-2-SPS Parallel Mechanism with adjustable fixed platform plat is built up and the simulation on the kinematic and dynamic performance is carried out. Curves of the Mechanism's kinematics and dynamics are acquired. Thus the validity of Pro/E simulation analysis is testified.