Research On Motion Resolution Of Stewart Parallel Mechanism

Parallel mechanism has been a hot research in international mechanics and robotics field in recent years. Accuracy is one of the most important performance indexes of parallel mechanism. And the motion resolution of mechanism is a part of the precision. Currently, majority of scholars study the systematic error of mechanism on error modeling of Stewart parallel mechanism at home and abroad. In addition, the model of random error is difficult, so the influence of random error on parallel mechanism is considered much more about the motion resolution of parallel mechanism, namely, the study of motion resolution of mechanism.Based on the study on motion resolution of Stewart parallel mechanism, considering the hinge clearance and the friction between the hinges, the motion resolution of mechanism is modeled, aimed at laying the theoretical foundation for the accuracy of the device with parallel mechanism and parts in processing, manufacturing and other parameters optimization. With the researching and analyzing on the two random errors about Stewart parallel mechanism, the main contents can be summarized as thus:1) Based on the assumption of the ideal move of parallel mechanism, namely, excluding the factors that influence the motion resolution of mechanism, servo system send pulse equivalent, namely resolution of driving system, to make a change in the positon and orientation of the moving platform, which is defined the motion resolution of mechanism. The motion resolution of the parallel mechanism along the axis of the spatial coordinate system is simulated by using the software of MATLAB and the anisotropy of motion resolution is analyzed. In the working space, the Newton-Raphson method is used to find out the change of the resolution, and the optimal working space of the mechanism is determined.2) Based on the kinematic theory of parallel mechanism, the method of error vector loop modeling is used to establish the mapping model of the motion resolution on the hinge clearance variable.3) Based on the mapping model of the motion resolution on the hinge clearance variable, the position of moving platform is solved by Newton-Raphson. In the entire non-singular workspace, quantitative analysis about the influence of hinge clearance on moving platform based on sensitivity index by using the software of MATLAB, and the optimization parameters of parts are done.4) Based on the kinetic theory of parallel mechanism, the method of Newton-Euler is used to establish the mapping model of the motion resolution on the friction between the hinges.5) Based on the mapping model of the motion resolution on the friction between the hinges, the position of moving platform is solved by Newton-Raphson. In the entire non-singular workspace, the influence of friction on moving platform is simulated, that is, the maximum value of motion resolution of mechanism, by using the software of MATLAB. The friction coefficient, working load, working speed, initial pose of mechanism and the number of spherical hinge suffered with friction are changed by the control variable method, and the effect of friction on the resolution is further analyzed by using the software of Adams.