Modeling And Analysis Of Mechanism For Vibration Isolation System Of Parallel Ship-based Stability Platform

Aiming at the working environment that the ship-based equipment is bearing at the same time in low-frequency and high-amplitude vibration and high-frequency and low-amplitude vibration,this paper studied the parallel stability and vibration isolation platform for ship-based equipment,the platform is used to isolate rigid connection between the ship hull and ship-based equipment,which ensuring the staff and precise goods in the ship-based equipment safety.According to the requirement of passive vibration isolation of ship-based equipment,this paper synthesizes several less-degree-of-freedom parallel mechanisms,and choose one named 4-RPC mechanism as the configuration for multidimensional vibration isolation(MVI)unit through comparative analysis.The mechanism is characterized in that each branch has moving pair and cylindrical pair that can be conveniently arranged for the vibration isolator.Moreover,the mechanism has redundant branches,the load bearing capacity of the vibration isolation system can be greatly improved.After having a detailed analysis of the freedom of 4-RPC parallel mechanism with screw theory,obtaining the properties of the freedom of the mechanism.Based on the configuration of MVI unit and the classical Stewart platform,carriing out the configuration synthesis for the vibration isolation system of ship-based stability platform.According to the principle that the active vibration isolation system of the mech--anism whether there is the upper or lower platform,the three types of configurations are parallel(serial-serial),parallel-parallel(serial)or serial-serial(parallel)and parallel-paral--lel-parallel have been integrated out.Then,changing the configuration and the number of the MVI units,several kinds of derivative mechanisms are synthesized.And discussing obtaining the properties of the freedom of the each mechanism.In this section,making a kinematic analysis of MVI unit.And the forward and inverse solutions of the MVI units configuration 4-RPC are analyzed,and the reachable workspace of the 4-RPC mechanism is obtained by using the inverse search method.The velocity mapping relation and acceleration mapping relation of the mechanism are analyzed by the method of virtual joints.And there are numerical-example verifications for kinematic analysis conclusions.In this section,making a dynamic analysis of MVI unit.Based on the lagrange method that analysed single degree of freedom system and planar parallel mechanism system conveniently,getting the vibration differential equations of MVI unit system based on lagrange equation.The equations are numerically analyzed by the four order Runge-Kutta method,getting the response curves in the time domain and the natural frequencies and mode shapes in the frequency domain that system is in forced vibration,and the influence of the stiffness coefficient and damping coefficient on the system is analyzed.Then the influence of stiffness coefficient and damping coefficient on the system is analyzed.In this section,through the analysis configuration of vibration isolation system of ship-based stability platform,choosing two kinds of simplified mechanisms Us-6_UPS and 6_UeUPS to make mechanism analysises.In the end,the vibration simulation of two typical simplified mechanisms are carried out,and the vibration isolation performance of the system is optimized by comparison.