Subsystem model-based close-loop grey-box identification method for hydraulic stewart platform

In order to solve the problem of difficult modeling and identification caused by time-variable parame- ters, multiple inputs and outputs and unstable open loop, a subsystem model-based close-loop grey-box identifi- cation method was put forward when consider the main coupling effects of hydraulic Stewart platform. Firstly, the whole system is divided into three TITO （Two Input Two Output） subsystems according to the characteris- tics of the pseudo-mass matrix, hence transfer function matrix model of the subsystem can also be found. Sec- ondly, since the Stewart platform is unstable, the close-loop transfer model of the subsystem is derived under the proportional controllers. The inverse M serial is adopted as the identification signal to get the experimental data. All parameters of the subsystem are determined in close-loop indirect identification by PEM （ Prediction Error Method）. Finally, a case study validates the correctness and effectiveness of the subsystem model-based close-loop grey-box identification method for hydraulic Stewart platform.