Research On The Milli-Newton-level Dynamic Thrust Measurement Device

With the development of science and technology,the exploration of space is more in-depth,and the vigorous development of propulsion technology accelerates the pace of aircraft mission completion in deep space exploration.In recent decades,the small thrust propulsion technology represented by electric propulsion has developed rapidly,and the development of electric propulsion technology has been mature and has broad application prospects.According to the propulsion requirements of small thrust spacecraft in different missions,such as lifting and orbit maintenance,attitude adjustment and resistance compensation,the thrust generated by the electric propulsion is required to be in the level of mN or?N.Compared with the traditional chemical propulsion,electric propulsion can output less thrust.In addition,electric propulsion has the advantages of small volume,light weight,high specific impulse and less propellant consumption.Therefore,the research and experiment of the electric thruster with the output thrust of mN and ?N have a high research value,and the tracking and monitoring experiment has an important practical significance for the development and improvement of the electric thruster.Starting from the practical application field,this paper takes the measurement of the micro thrust output of the electric thruster as the research goal.By summarizing the existing micro thrust test methods at home and abroad and the force measurement methods of piezoelectric sensors,the advantages and disadvantages of the existing micro thrust test devices are comprehensively analyzed,and a Nano-level micro thrust test device is designed,which can realize the separation between the thrust direction and the gravity direction of the thruster.The piezoelectric sensor with a circular hole in the middle is used as the measuring sensitive element in the measuring device.After pre tightening,the lower cover and the bottom plate are connected by bolts,and the upper cover and the bar are rigidly connected to transmit the required measured torque.Through the crossbeam connected to the bar,the force is changed to the torque,which enlarges the micro thrust to be measured,and then the micro thrust can be obtained.In the process of designing the measurement device,the crossbeam of is optimized by MATLAB software.During the calibration of the device,the static and dynamic calibration experiments are completed by using a standard weak force generator.Secondly,in the dynamic calibration experiment,the inherent experimental frequency of the micro thrust measuring device is measured,so as to obtain the appropriate loading frequency range of the force source and determine the dynamic response frequency band width of the thrust measuring device.In this paper,two methods are used to measure the natural frequency of the device,i.e.knock test method and finite element analysis method based on ANSYS.In this paper,the force source device used in the calibration experiment,the electromagnetic force generation device,mainly produces small force by the way of electromagnet sucking and guiding the magnet block.The electromagnet is a DC electromagnet.In the static calibration experiment,the DC electromagnetic iron is connected with the DC current,which can calibrate the tiny thrust generated by the precise electronic balance,and then obtain the corresponding linear relationship between the thrust and the output voltage of the sensor.However,in the dynamic calibration experiment,it is difficult to predict the result of the current generated by the DC electromagnetic iron of the electromagnetic force generator when it is connected to the AC current.In this paper,the static calibration results are used to predict and analyze the dynamic experiment.Moreover,based on the results of static experiment and the electromagnetic simulation module of COMSOL,the results of experiment are simulated and analyzed,and the dynamic model of measuring device is analyzed,and the dynamic calibration experimental results are reasonably explained.The static calibration results show that the nonlinear error is 1.26%,and the repeatability error is 1.43%.The minimum thrust sensed by piezoelectric quartz sensor is about 0.02 mn.The results of dynamic calibration experiment show that when the current frequency of the power source device is 0-5Hz,the measurement results basically conform to the theoretical speculation.As the frequency continues to increase,the experimental data is affected by the output force distortion and resonance.