| 6-DOF of Stewart platform is a parallel mechanism with 6 degrees. Because it possesses high positioning capability provided by their high structural rigidity and high strength-to-weight ratios, it has already been widely used in kinds of engineering fields, one of which is the applications of motion simulator. Since motion simulator focuses on reproduction of motion, it makes great sense to calculate its first and second derivative of kinematic parameters for improvement and evaluation of performance of motion simulator. Recently, these kinematic parameters are difficult or expensive to be measured. The numerical method to calculate these parameters real-time is presented in this paper.Stewart platform error model has been built up based on the simplified error source model. According to the model, the error translation matrix is the function of parameters of the platform by analyzing the model. Beside, the platform error output influenced by structure parameters has been computed. It can be got from the simulation that recommended parameter design value obtained in the way mentioned above is close to the ones got though the tradition design. Theory support is provided in this paper when platform parameters are designed.A FIR low-pass filter is designed for the experiment following the criterion of maximal-error-minimization. The order and the impulse response sequence of the filter are presented in this paper. The amplitude frequency response characteristic of impulse sampling sequence of low-pass filter is drawn. The methods with which filter can be put into effect are introduced.An experiment is carried out to test the feasibility of the spline approximation to calculate the kinematic parameters. The result indicates that this method is feasible. The first derivative of kinematic parameters can been calculated well while the second ones can't which need filter.
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