Research On Ship Motion Simulator With Three Degrees Of Freedom And Its Hydraulic Servo Driven System

Based on various purposes, SMS (Ship Motion Simulator) was developed by a lot of domestic and overseas companies and institutions. Traditionally, the Steward parallel mechanism is adopted, because it possesses the advantages of high rigidity, high load-capacity, and structural simplicity. The disadvantages are that there exist strong coupling among different actuators, and the amplitude of heaving is limited by the range of actuator movement. With the requirement of research on seasickness, a novel-structure SMS is designed. This SMS achieves the large motion of heaving simulation through " scissor " mechanism and the large motion of pitching and rolling simulation through "seesaw " mechanism. The position tracking valve controlled asymmetrical hydraulic cylinder system with high precision is applied to the designed SMS and is also required greatly in the modern national defense and civil industry. Hence it is very necessary to study the valve controlled asymmetrical hydraulic cylinder system thoroughly. Based on the SMS and its hydraulic servo driving system, a series of researches are carried out as follows:1. The kinematics is analyzed for the SMS, and forward kinematics and inverse kinematics are discussed. The dynamic equation is set up through the D'Alembert's principle. In the process of dynamics analysis, the method to directly adopt sequential coordinates rotation transformation is presented to obtain the attitude angular velocity and angular acceleration of the pitching and rolling servo cylinders, and the idea that the pitching and rolling mechanism and the load on upper platform is wholely regarded as a dynamic load on the heaving mechanism is presented to simplify the dynamics analysis for the heaving mechanism. Finally, the kinematics and dynamics are simulated. Results of simulation give the load range of cylinders and show that weak coupling exists between both the cylinders of the pitching and rolling mechanism and the motion magnification is about 2.2. One nonlinear model suitable for forward and inverse motion is deduced for the valve controlled asymmetrical cylinder system, and the model is proved correct by comparing simulation with experiment. Aiming to clarify the confusion of definitions of load pressure and load flow in nowadays correlative literatures, the principle for defining load pressure and load flow is given to establish the local linearized model by Taylor expansion approximation. The global linearized model is established by nonlinear state feedback transformation, and the stability is analyzed for its zero dynamic state. The effect on the system's performance caused by some nonlinearities is simulated through the established nonlinear state-space model.3. Using bifurcation theory, process of effect on the system's stability caused by various uncertain factors is described and analyzed, and some conclusions are drawn as follows. Under the same extent of change of parameters, the effect on stability is greater when cylinder moves forward than that when cylingder moves backward.The longer oil inlet pipe, the worse the stability, and the degree that the stability becomes worse is very small when the length of pipe exceeds a certain value. The bigger the diameter of oil inlet pipe, the better the stability, and the degree that the stability becomes better is very small when the diameter of pipe exceeds a certain value. The stability also becomes bad when the fluid bulk modulus reduces. Finally some parameters' stability field is given.4. The process of determining uncertainty model in domestic and overseas literatures on quantitative feedback theory (QFT) is analyzed and summarized in detail. On the above basis, four ways are presented to derive the system's uncertainty model, and at the same time, the advantages and disadvantages of the four ways are concluded. The QFT position tracking robust controller is designed. After finding notable tracking phase error, the zero phase error tracking controller is designed to replace the feedforward filter, and a zero phase-shift low-pass filter is designed to reduce the high frequency gain of the zero phase error tracking controller. An improved saturation compensator is designed to bate the saturation nonlinearity in the valve controlled asymmetrical cylinder system. In designing all the controllers, the equivalent transfer function is applied to simplify the controller structure. A lot of experiments are done for every part of the controller during the designing process by means of the developed SMS prototype. The comparative experiment is done between high precision position tracking robust controller and self-learning fuzzy sliding mode controller, and the result shows that the precision of the former is higher with the same load disturbance. Finally, the experiment is done for simulating motion causing seasick, and it indicates that the SMS prototype can meet the motion requirements for researching seasick.