Research On Model-based Adaptive Control Of Six-degree-of-freedom Hydraulic Motion Platform

Along with the rapid development of Hardware-in-loop simulation technology, motion simulators are widely used military and civil fields such as in aeronautics, astronautics, maritime, vehicle and amusement, etc for their production development and training. The six-dof (six-degree-of-freedom) hydraulic motion platform is used as a motion system for almost all motion simulators for its advantages such as high stiffness, high power density and capable of simulating all space movements, etc. The dynamic performance of the six-dof hydraulic motion platform has a direct relationship with the degree of versimilitude in motion simulation, and the advanced movement control strategy is one of the most key technology to realize the best dynamic performance.Therefore, a widely and in-dept research on the control theory and parameter identification for the six-dof hydraulic motion platform to improve the performance has a great significance.Base on the large amount of relative references at home and abroad, this paper outlined the architecture and characteristics of the six-dof hydraulic motion platform, depicted its developing status and application. In the meantime this paper summarized the key technology for the six-dof hydraulic motion platform, and then put up the main study content of the whole paper.The mechanical dynamics model is an important research area of the control strategy for the six-dof hydraulic motion platform. First of all, after the setup of the mechanical dynamics model including the leg's influence, the influence of the leg and each part of the dynamics equation to driving force was analyzed to simplify the architecture of the dynamics model. The expression of the dynamics model was also analyzed to draw such a conclusion that the leg's inertia and moment can be seen as an equivalent increment of the upper platform, and then derived an linearized dynamics equation expressed by the vector of the upper platform's inertia parameters, which paved the way to give an research on to the parameter identification and model-based controller design.Accurate value of the model parameter is a prerequisite for control strategy research. To identify all the model parameters for the whole system, the system model is divided into two parts: hydraulic model part and mechanical load part. The identification model and the validation model for hydraulic nonlinear drive model are setup. The genetic identification method was used to identify the hydraulic nonlinear model parameters. The experimental data validates the effectiveness of the identification method. As far as the mechanical dynamics parameters were concerned, a step by step identification method combined with dynamic filtering technique was proposed to identify the inertia parameters to overcome the disadvantages of the difficult design and reach of optimum trajectory for identification. All parameters of these two parts from the identification provided the basis for for model-based nonlinear controller's design.As a key technology of the six-dof hydraulic motion platform, this paper mainly studied the joint-space contrller and task-space controller to cater for the application in different circumstances.Aim to solve the problem of the leg's large parameter perturbation and load changes during the work of the hydraulic six dof motion platform, a backstepping adaptive controller based on joint-space nonlinear model was proposed according to Lyapunov stability.The proposed controller compenated the dynamic coupling force and avoided the acceleration feedback by introducing the dynamic surface. The simulation results indicated that it can effectively suppress the influence from large parameter variance, dynamics coupling force among legs and external disturbance. The dynamic performance of the six-dof hydraulic motion platform was improved. As to deal with the dynamic cross-coupling force and parameters uncertainties, a backstepping adaptive controller based on task-space nonlinear model was put forward according to Lyapunov stability. The proposed controller was capable for everywhere in workspace for it is constructed on the basis of the complete nonlinear dynamics model, and avoided the acceleration feedback by introducing the dynamic surface. The simulation results indicate that it can effectively restrain the influence from parameter uncertainties, dynamics nonlinearity and load cross coupling among degrees. The dynamic performance was improved to attain a better tracking ability.At last, the experimental research was carried out on the six-dof hydraulic motion platform. The experimental results were analyzed. It validated the correctness of the theory analysis and parameter identification. It is shown that compared with the ordinary control methods, the proposed two controllers,namely the joint-space and task-space adaptive controller can more effectively depress the dynamic coupling force and thus improve the dynamic performance of the hydraulic six dof motion platform.