The edge displacement sensor, serving as a core component in large-aperture astronomical telescopes, plays a crucial role in maintaining the co-focusing of mirrors by measuring tiny displacements between sub-mirrors. Therefore, the performance of the sensor is of paramount importance to ensure that the telescope can obtain clear and accurate images. The challenging on-site environmental conditions place high demands on the sensor's performance. The key characteristics of the edge displacement sensor include nanometer resolution, low nonlinearity, minimal temperature drift, and temporal stability. Simultaneously achieving all these performance criteria poses significant challenges. We have developed an ultra-stable eddy current edge displacement sensor with a resolution better than 1nm (RMS) within a range of 250μm. During on-site testing at the Guoshoujing Telescope (the Large Sky Area Multi-Object Fiber Spectroscopic Telescope LAMOST) telescope, the sensor exhibited a temperature drift within ±2nm/°C after temperature compensation and achieved a drift of less than 25nm over 5 weeks. The environmental temperature varied within the range of - 17~+14°C, and humidity fluctuated between 20% and 80% RH during the testing. Additionally, a co-focusing test was conducted on a small system composed of three selected sub-mirrors. Six sets of sensors were installed on this small system, enabling real-time measurement of sensor outputs for attitude correction. The test results indicate that, by relying on sensor feedback, the telescope has the potential to achieve high-quality co-focusing over extended periods and significant temperature ranges, thereby enhancing the operational efficiency and observation quality of the telescope.
Adaptive optical systems are originally developed for the field of astronomy to eliminate image blurring aberrations induced by atmospheric disturbance. In some complex applications, such as the contactless thin adaptive mirror for large-aperture ground-based optical telescopes, displacement sensors are needed to measure the deformation of the deformable mirror and construct a local position control loop. In the past adaptive secondary mirrors, capacitive sensors are designed to measure the mirror deformation. However, they suffer problems of manufacturing, maintenance, and environment. In this paper, a high-performance eddy current displacement sensor is proposed for the deformation measurement of adaptive secondary mirrors. Simulation and optimization of the detecting coil and conductive target are carried out. A deliberate signal processing circuit is designed for weak signal detection. Experimental results of the prototype sensor indicate a resolution up to 5 nm and a linearity better than 0.1% within the measuring range of 50 μm and bandwidth of 3 kHz, which meet the basic technical requirements of the adaptive optical systems.
Torsional vibrations of circular tubes, rods, rings, and disks are widely used as operation modes of acoustic wave transducers in various piezoelectric devices. In this paper, a piezoelectric disk with spiral interdigitated electrodes is proposed to generate in-plane torsion in a simple and effective manner. Design and working principle of the torsional transducer are introduced. Vibration characteristics of the transducer with a constant spiral angle are studied. A simplified model is established to investigate the basic dynamic characteristics of torsional vibration accompanying with radial vibration. Electric admittance, resonant frequencies, and mode shapes with different boundary conditions are calculated. Resonant frequencies as functions of several structural parameters are discussed.
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