Internal and external disturbances rejection control for pitch frame of horizontal hydraulic flight motion simulator

The horizontal hydraulic flight motion simulator (HHFMS) is preferred in the situations of large power and high dynamic for the hardware-in-the-loop simulation of the aerospace field. However, multiple modeling uncertainties prevent HHFMS from receiving accurate simulation of aircraft attitude. Particularly, due to suffering from serious and complex disturbance, pitch frame of HHFMS is more difficult to achieve high-precision control compared with yaw frame and roll frame. Aiming at this issue, through defining the disturbance only related to states of pitch frame itself as internal disturbance and the one also related to states of other frames as external disturbance, in view of theory and application, internal and external disturbances rejection control (IEDRC) was investigated for pitch frame. In the proposed control method, by means of backstepping, nonlinear disturbance observers (NDOs) were designed to handle internal disturbance from parametric uncertainties involving hydraulic flow, as well as friction torque and gravity torque when yaw frame is at zero position and load is replaced. Additionally, robust integral of the sign of the error (RISE) was assigned to suppress external disturbance composed of coupling torque, as well as the variations of inertia torque and gravity torque caused by position change of yaw frame. Here, RISE can assist NDO to overcome its limitation in dealing with the time-varying disturbance, and NDO can alleviate chattering risk resulted from the sign function in RISE. The two complement each other. As a result, via rejecting internal and external disturbances caused by hydraulic parameters, load replacement and simultaneous movement of three frames, IEDRC can not only guarantee an excellent control performance, but also avoid the huge workload spent on the acquisition of model parameters. Finally, comparative experiments including a few Cases were conducted, which demonstrates the overall performance of the developed control method.