| With the continuous development of electric integration technology,micro satellites have shown great scientific potential in the aviation field.More and more space science tasks are carried out by small satellites,which puts forward higher requirements for satellite attitude and orbit control ability and working noise suppression.A reasonable measurement system is designed to measure the thrust output and the corresponding thrust noise,which has high guiding significance for the evaluation and optimization of propeller performance.Aiming at the output performance of a plasma propeller with controllable thrust output independently developed by Lanzhou Institute of space physics,a micro thrust measurement device based on torsion pendulum structure is designed in this thesis.The measurement system adopts closed-loop control and is composed of torsional pendulum structure,displacement sensing system,eddy current damper and weak force compensation system.The damper is used to suppress the interference of environmental noise and improve the stability of the system.The thrust of the electric propeller acts on the torsion pendulum structure.After the change is detected by the displacement sensing system,the position signal is fed back to the weak force compensation system,and then the equivalent weak force is output to compensate the thrust.The corresponding thrust can be obtained by calculating the compensation current.Then,through the spectrum analysis of the collected thrust signal,combined with the dynamic response characteristics of the measuring device,the thrust noise of the electric propeller can be obtained,and then the performance of the propeller can be evaluated.The main contents of this paper are as follows:1.Give the overall design scheme of the measurement system,deduce the mathematical model and theoretical analysis of the key modules,and draw the following conclusions:（1）deduce the vibration equation of the torsion pendulum structure,and draw the conclusion that there is a linear relationship between the single degree of freedom offset of the torsion pendulum and the action of external force;（2）The principle of optical lever used in photoelectric sensor can improve the measurement sensitivity;（3）The principle of eddy current can provide a theoretical basis for the preparation of damping device;（4）The combination of permanent magnet and double coil can output linear electromagnetic standard force,and cooperate with PID control circuit to form weak force compensation module.2.The thrust measurement system is assembled.The experimental results show that the balance recovery time of the torsional pendulum displacement platform under the action of damping is shortened from 9.2 s to 3.8 s,and the damping effect is ideal.A more scientific electromagnetic weak force calibration method is designed.The calibration results show that the functional relationship between the current and the corresponding output electromagnetic force is y = 36297.2x + 9815.3,and the linear fitting determination coefficient is 1.Finally,the average thrust measurement of ion thruster under different working conditions is completed.3.Based on Lab VIEW development environment,the thrust measurement software is designed,including DA,AD module data communication,data processing and other functions,and the corresponding operation process is given.4.The measured natural frequencies of the system without damping and PID,with damping and PID are 0.5 Hz,0.38 Hz and 0.89 Hz respectively.The natural frequency will affect the system response after verification.The sine wave force source device composed of software design,DA conversion and electromagnetic weak force device has no distortion in amplitude and frequency response in the frequency band of0.0005～0.5 Hz.The thrust measurement system excited by sine wave has no distortion in the frequency band of 0.0005～0.1 Hz,and can be used to measure the thrust noise of electric propeller. |
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