Thrust Evaluation in Wide Frequency Range Using Active Control and Disturbance Observer

摘要

In this paper, a new method is proposed for evaluating thrust in the wide-frequency range from 0 Hz beyond the pendulum resonant frequency. The proposed method uses position control and a disturbance observer based on pendulum acceleration and solenoid-actuator current A controller monitors pendulum motion and adjusts the force of a solenoid actuator in such a way that the pendulum angular displacement is kept constant Simultaneously, the disturbance observer evaluates both invariant and time-varying components of thrust by use of pendulum acceleration and solenoid-actuator current Spring and damping coefficients originating from wires, tubes, and the thrust stand can be ignored due to the position control. A calibrator, yielding both constant and periodically varying, biased forces, was also prototyped to show that the proposed method can evaluate thrust in a wide-frequency range from 0 Hz beyond the resonant frequency. The prototype thrust stand successfully measured thrust in the frequency range from 0 to 65 Hz with errors less than 16%, whereas the conventional null-balance method yielded 810% overestimation of thrust amplitude at a resonant frequency of approximately 15 Hz.