The Technology For Detecting Two-degree-of-freedom Angular Displacement Of Spherical Pair Based On A Spherical Capacitive Sensor

The aviation photoelectric load mainly adopts the universal rotation mechanism of two axes-four frames to make the optical gear inside simultaneously generate two-dimensional angular movements of pitch（a₁）and roll（a₂）to achieve accurate tracking of space targets.The primary function of the outer frame is to rotate in a large range and isolate the wind resistance disturbance.The inner frame can be used to realize the precise inertial stabilization and tracking function and ensure the photoelectric load’s orientation and stability in the inertial space through the operating mode of the outer frame following the inner frame.However,the traditional inner frame structure mainly adopts an orthogonal frame structure.Due to the massive size of the frame and the long transmission path,the inner frame needs to have sufficient rigidity to ensure enough stability of the photovoltaic pod,which means that the inner frame has enough rigidity.The structure will occupy the aviation optoelectronic pod’s more prominent space and weight.Compared with the frame structure,the spherical motion pair has significant technical advantages such as small size,many degrees of freedom of motion,and short transmission path.Still,its two-dimensional angular motion signal is difficult to detect,making it unable to be used in aviation optoelectronic pods to replace the frame as an internal stabilization agency.Although optoelectronic systems including SOFIA have developed multi-degree-of-freedom laser angle measurement technology for spherical motion pairs,its large size makes it difficult to achieve miniaturized applications in aviation-constrained environments.In this paper,by investigating the development status of spherical kinematic pair and its measurement technology at home and abroad,combined with the application requirements of the angle measurement of the inner frame of the aviation optoelectronic pod,a miniaturized two-degree-of-freedom angle measurement technology based on the capacitive differential measurement principle is studied.Main research work:1.Based on the structure and transmission characteristics of the spherical motion pair,a spherical capacitive sensor with a four-quadrant differential structure is proposed,and a mathematical measurement model of the two-dimensional angular displacement signal and differential output capacitive signal of the spherical capacitive sensor is es-tablished.Construct a signal decoupling calculation method,and provide a theoretical basis for the detection of angular displacement signals.2.The initial structural parameters of the spherical capacitive sensor are designed,and the spherical capacitive sensor is analyzed based on the finite element electromag-netic model;the electromagnetic simulation results are compared with the theoretical model of the sensor,and the feasibility of the two-dimensional angular displacement signal detection scheme of the spherical motion pair is verified.3.Aiming at the problem that the weak capacitance signal is difficult to detect,an FPGA digital cross-correlation solution algorithm is designed and a driving circuit is designed to realize the real-time decoupling of the two-dimensional angular displace-ment signal of the spherical motion pair.In order to detect the f F capacitance signal,the hardware detection system of the capacitive sensor is built.4.A measuring device of spherical capacitive sensor is built to detect two-dimensional angular displacement signals,and the influence characteristics of”axial”installation error and”radial”installation error on output characteristics are analyzed,and the dis-tribution requirements of errors are determined.The static and dynamic indexes of the spherical capacitive sensor are tested.The test results show that the designed capacitive sensor can achieve a measurement of 0.002°angular displacement resolution within the measurement range of±4°.The corresponding stabilization time of the pulse is 39,and the”inverse non”correction method is proposed for the problem of temperature drift,and the temperature drift after compensation is 0.00008°/℃.In summarize,this paper profoundly studies the design theory and method of a spherical capacitive sensor and uses the finite element electromagnetic simulation model to optimize the structure and installation error distribution of the capacitive sensor.The hardware and software technology of modulation and demodulation of the capacitive sensor with a small-angle motion range is studied.And set up an experimental device and obtained good practical results.The subject breaks through the technical bottleneck of two-dimensional angular motion signal detection of small-angle spherical motion pairs and lays an essential technical foundation for applying spherical motion pairs in aviation optoelectronic loads.