基于扭摆台架的动态推力测试方法研究

Study of Dynamic Thrust Measurement Using Torsional Pendulum

关键词:  微推力器  动态推力  扭摆台架  干涉式激光位移计

Key words:  Microthruster  Dynamic thrust  Torsional pendulum  Laser interferometry

摘要:

微纳卫星微推力器的性能测试，要求在诊断稳态推力和冲量的同时测量动态推力，为此开展动态推力测试方法研究。根据扭摆式台架的二阶质量-弹簧-阻尼系统模型及特点，提出通过静、动态砝码标定，进行扭摆台架的转动惯量、阻尼常数和弹簧系数等参数辨识。利用干涉式激光位移计实现对微小位移的高精度和高频响测量，系统的测量精度约为10nm，测试带宽500kHz。建立了探测器的记录光强与微位移间的数学模型，获取台架微位移，通过对微位移进行一次、二次求导获得台架的速度和加速度信息，根据台架运动方程，实现动态推力测量。误差分析表明，稳态推力测试的最大绝对误差小于0.5mN，动态推力测试的最大误差约为0.58mN。利用落压式工作的微型冷气推力器开展验证试验，结果表明该测试方法能够实现动态推力测量要求，响应频率为50Hz。

Abstract:

Performance emulation of microthrusters used in micro-nano satellite requires diagnostics of steady thrust，impulse and dynamic-thrust. Measurement technology study was conducted to satisfy this requirement. Based on the torsional pendulum’s property as a mass-spring-damping system，a method was proposed to estimate parameters of the pendulum’s moment of inertia，damping constant and effective spring coefficient by performing static and dynamic calibrations with weight. An interferometer was applied to measure the small displacement with high precision and high frequency，of which the precision was about 10nm and the bandwidth was 500 kHz. The relation between light intensity recorded by detectors and small displacement was modeled to acquire the displacement of the pendulum. Hence，first-order and second-order derivatives of small displacement could be made to obtain velocity and acceleration，which realized measurement of the time-resolved force acting on the pendulum using motion equation of torsional stand. Error analysis shows that maximum uncertainty is 0.5mN for steady thrust measurement and 0.58mN for dynamic-thrust. Verification experiment was made using an ultra-high pressure cold gas thruster which show this method can be used to measure dynamic thrust at a response frequency of 50Hz.