Kinematics Analysis of Parallel Position Adjustment and Vibration Isolation Platformwith High and Low Frequency Compound Drive

Existing disturbance compensation devices have a defect that the functions of the position adjustment and the vibration isolation are separated. To address the defect, a parallel platform with high and low frequency compound drive is developed. By comparing the performances of several compound driving methods, a planar five-link mechanism with RRPRP configuration is selected as the compound drive unit, and the configuration of the mechanism is determined as 3-RRPRP-4S. Firstly, the constraint screw theory is used to analyze the equivalent form of the high and low frequency compound drive unit and the degree-of-freedom of the mechanism. Then, the position inverse solution models of the two driving forms, high frequency and low frequency, are established. Here, the step-by-step iterative method is used for analysis in the high frequency driving form. Secondly, the 1st-order and the 2nd-order influence coefficients between the moving platform and the generalized inputs are constructed under the two kinds of driving forms based on the screw theory, then the linear mappings, from the generalized inputs to the velocity and the acceleration of the moving platform respectively, are obtained. Next, the instantaneous locking method is put forward as the driving strategy of the mechanism based on the kinematics analysis results. Finally, the kinematics analyses are verified by the simulations on the numerical examples under the high and low frequency drive, and by the experiments on a prototype. Results show that the simulation curves and the theoretical curves almost coincide, while the recurrence rate is 93%~96% in the prototype experiment. Therefore, the platform with the high and low frequency compound driving, realizes a hybrid output of the position adjustment and the vibration isolation. In fact, it breaks through the limits to the existing disturbance compensation devices caused by the frequency band of drives, and can compensate the interference signals within a large frequency range.