Research On Control Of Shipborne Six-degree-of-freedom Stabilized Platform

The main role of the shipborne stability platform is to provide a relatively stable working condition in the environment of wave disturbances.It is widely used in the fields of exploitation of marine resources,shipborne weapons stabilization,satellite communications,and shipborne helicopters.The shipboard stability platform has farreaching significance both for economic development and military defense.At present,the mainstream structure of the shipboard stable platform is still a series rotary table based on gyroscope,but a stable platform that uses this structure alone only can compensate for disturbances up to three degrees of freedom at most.The parallel mechanism based on the Stewart has six degrees of freedom motion in space,so it can be used as a stabilized platform in theory to achieve full compensation for disturbances.The shipboard stability platform studied in this paper is based on this typical parallel mechanism.Although the six-degree-of-freedom stability platform can achieve full compensation of disturbances,it still faces technical difficulties in design and control.In this paper,firstly,the structure and working principle of the six-degree-offreedom stability platform are described.Then,based on the definition of the stable platform coordinate system,a kinematics model including forward and inverse solutions is established.And a single rigid body dynamic model of stable platform was establisshed.In order to maximize the advantages of the parallel mechanism,hydraulic servo actuators are used as the actuator for the stable platform.Firstly,a unified mathematical model of valve-controlled asymmetric power mechanism was established,which include positive and negative direction.And then the working characteristics of the power mechanism were briefly analyzed.After that,the differential pressure feedback and feedforward compensation links are used to calibrate the hydraulic single-channel system,which is intended to increase the response speed of the system as much as possible.In addition,a Simulink and ADAMS co-simulation model for stable platform system was built,and the correctness of the aforementioned model was verified by simulation.Through the co-simulation analysis,it is found that the system response delay is one of the main factors affecting the stability accuracy of the stable platform.Taking into account the ship motion under the influence of waves is predictable at some point,it is proposed to compensate for the system's lag via prediction.In this paper,we use the timeseries autoregressive model to predict the ship motion trend.In order to obtain the prediction model,we need to complete the work of model determination and model parameter identification.AIC information criterion is adopted to determine optimal model order,which weights the complexity and accuracy of the model.The following two methods were used to identify model parameters: one is a parameter estimation method based on weighted recursive least squares;the other is a method based on Kalman filtering estimation principle.Through simulation analysis,we can see that the models determined by these two parameter estimation methods can effectively improve the stability accuracy of the platform.Due to the addition of statistical features,so the latter prediction is relatively better than the former.At last,the experimental verification of the proposed prediction compensation control algorithm is carried out through experiments.The experimental data show that the prediction compensation control algorithm used can effectively improve the stability accuracy of the system,and the prediction compensation control algorithm has a certain degree of practicality.