外乱オブザーバと定置制御とを併用した広帯域の推力測定

概要

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In this paper, we propose a new thrust stand measuring not only constant thrust but also wide-frequency-range thrust variation beyond the resonant frequency. The designed thrust stand uses active control, disturbance observer and measurement of acceleration and solenoid current. A controller monitors pendulum motion and adjusts force of a solenoid actuator in such a way that the pendulum deflection angle is kept constant. Spontaneously, disturbance observer evaluates thrusts with variations directly from measures: acceleration and solenoid-actuator current. Thrust is directly determined from the current and acceleration because spring constant and damping factor originating from wires, tubes and the thrust stand can be ignored due to null-position active control. A calibrator, yielding both constant force and sinusoidal force with offset, was also designed to show that the designed thrust stand can evaluate both constant thrust and its variation beyond the resonant frequency. The prototype thrust stand successfully measured thrust with its variation in the frequency range from 0 to 75Hz, whereas conventional null-position method yielded 410-% overestimation of thrust variation with a phase shift of 120deg at a resonant frequency of 30Hz.