| Adaptive optical system with voice coil motor can correct the wave-front difference in real time by measuring the wave-front distortion and adjusting the deformable mirror shape,which is especially suitable for the ground correction of large optical / infrared telescopes.When the voice coil motor works,a displacement sensor is needed to form a local feedback loop to improve the accuracy and speed of shape control for the adaptive mirror.As the core component of shape control for the adaptive mirror with voice coil motor,currently used capacitive displacement sensor has some problems,such as high cost of manufacture and maintenance,very sensitive to environmental media,which seriously restrict the development and application of adaptive optical technology for large optical / infrared telescopes.In this paper,an eddy current sensor is proposed to replace the traditional capacitive sensor,which has the advantages of low cost of manufacture and maintenance,not affected by dust and oil pollution,and so on.By overcoming the problems,such as the magnetic interference of the exciting coil of voice coil motor on the detecting coil of the eddy current sensor,an eddy current displacement sensor is developed suitable for the deformation measurement of adaptive mirror with voice coil motor.The main work of this paper includes:1.The basic theories of eddy current displacement sensor are summarized,and the finite element simulation model of the detecting elements is established.The eddy current distribution law and impedance variation characteristics of detecting elements are analyzed,and the material and structural parameters of the detecting coil and target conductor are optimized.The distribution characteristics of magnetic field of voice coil motor are studied,and the coupling law of magnetic field interference of detecting coil is analyzed.2.The signal conditioning methods of eddy current displacement sensor are summarized.The signal conditioning circuits based on AC bridge are designed and analyzed,including signal modulation and demodulation circuit and multi-stage signal amplification and filtering circuit,and the suppression method of circuit noise and magnetic field interference under high bandwidth is studied.3.A prototype sensor is manufactured,and the linearity,sensitivity,noise and other basic performances of the sensor are tested.The simulation experiment platform of adaptive mirror with voice coil motor is built,and the noise characteristics and deformation measurement performances of the sensor under the interference of voice coil motor are tested.The experimental results show that the resolution of the prototype sensor reaches 5 nm and the linearity after compensation reaches 0.1% in the 50 ?m measurement range and 3 k Hz bandwidth,the resolution is still within 10 nm under the strong magnetic field interference of voice coil motor,which meets the technical requirements of the adaptive optical system.The eddy current displacement sensor proposed in this paper overcomes the inherent defects of the traditional capacitive sensor and shows good comprehensive performance.It is expected to have a good application in the adaptive optical system with voice coil motor. |
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