ABSTRACT
Conventional eddy-current sensors have the advantages of being contactless and having high bandwidth and high sensitivity. They are widely used in micro-displacement measurement, micro-angle measurement, and rotational speed measurement. However, they are based on the principle of impedance measurement, so the influence of temperature drift on sensor accuracy is difficult to overcome. A differential digital demodulation eddy current sensor system was designed to reduce the influence of temperature drift on the output accuracy of the eddy current sensor. The differential sensor probe was used to eliminate common-mode interference caused by temperature, and the differential analog carrier signal was digitized by a high-speed ADC. In the FPGA, the amplitude information is resolved using the double correlation demodulation method. The main sources of system errors were determined, and a test device was designed using a laser autocollimator. Tests were conducted to measure various aspects of sensor performance. Testing showed the following metrics for the differential digital demodulation eddy current sensor: nonlinearity 0.68% in the range of ±2.5 mm, resolution 760 nm, maximum bandwidth 25 kHz, and significant suppression in the temperature drift compared to analog demodulation methods. The tests show that the sensor has high precision, low temperature drift and great flexibility, and it can instead of conventional sensors in applications with large temperature variability.
ABSTRACT
The ball joint is a multi-degree-of-freedom transmission pair, if it can replace the inner frame in the aviation photoelectric pod to carry the optical load, which will greatly simplify the system structure of the photoelectric pod and reduce the space occupied by the inner frame. However, installation errors in ball joint siting introduce nonlinear errors that are difficult to correct and two degree of freedom angular displacement of the ball joint is difficult to detect, which limits application in the precision control of two degrees of freedom systems. Studies of spherical capacitive sensors to date have not tested sensors for use in an inner frame stabilisation mechanism nor have they analysed the influence of installation error on sensor output. A two-axis angular experimental device was designed to measure the performance of a ball joint capacitive sensor in a frame stabilisation mechanism in an aeronautical optoelectronic pod, and a mathematical model to compensate for ball joint capacitive sensor installation error was created and tested. The experimental results show that the resolution of the capacitive sensor was 0.02° in the operating range ±4°, the repeatability factor was 0.86%, and the pulse response time was 39 µs. The designed capacitive sensor has a simple structure, high measurement accuracy, and strong robustness, and it can be integrated into ball joint applications in the frames of aeronautical photoelectric pods.
ABSTRACT
The spherical pair has an important role in the inner frame of the stabilization mechanism of the aviation optoelectronic pod. However, its two-degrees-of-freedom (2-DOF) angular displacement signal is difficult to detect, seriously restricting its application in aviation optoelectronic pods. Therefore, this study proposes a new method to measure a spherical pair's 2-DOF angular displacement using a spherical capacitive sensor. The capacitive sensor presented by this method realizes the measurement of the 2-DOF angular displacement of the spherical pair by integrating the spherical electrode groups in the ball head and the ball socket of the spherical pair. First, based on the geometric structure of the spherical pair, the structure of the capacitive sensor is designed, and the mathematical model for the capacitive sensor is deduced. Then, the sensor's output capacitance, in different directions, is simulated by Ansoft Maxwell software. Finally, an experiment device is built for the measurement experiments. The simulation analysis and experimental results show that the spherical capacitive sensor has an approximately linear output in different directions, and the measured output capacitance is as high as 89.7% of the theoretical value. Compared with the existing sensors that measure the 2-DOF angular displacement signal of the ball pair, the sensor proposed in this study has an integrated structure, which can be integrated into the spherical pair. That makes it possible to apply the spherical pair to the inner frame of the aviation optoelectronic pod.
ABSTRACT
This paper proposes a design process for additively manufactured mirrors. A central support aspheric mirror and tripod support structure were manufactured via selective laser melting. To achieve substantial weight reduction, an additively manufactured body-centered cubic lattice structure was used in the mirror design. Simulation analysis showed that the mirror had good rigidity. Single-point diamond turning was applied to obtain an optical quality mirror. After assembly, the rms surface shape accuracy of the mirror was 0.069λ (λ=632.8nm). The surface roughness (Ra) of the additively manufactured metal mirror was 8.125 nm. These findings provide a strong theoretical basis and technical support for the preparation and application of lightweight metal mirrors.
ABSTRACT
We propose analysis methods for mirror bonding. The functional relationship between the shrinkage of the adhesive layer and the shape accuracy of the mirror is established numerically. By designing the structural form of the optical mounting and setting an appropriate stiffness ratio between the mirror and bonding position of the optical mounting, the theoretical surface shape accuracy change can be determined. Accordingly, the mirror is bonded, and the surface shape accuracy of the mirror after bonding is found to be 0.020λ. This approach is useful in mirror design applications that require rapid preparation and accuracy control.
ABSTRACT
This paper presents a method for the automatic design of a special mid-wavelength infrared zoom system in which the positions of both the pupil planes and the image plane are fixed during the zooming process. In this method, the formulas for the desired zoom system are derived to ensure the exact fulfillment of the conditions with three moving components based on Gaussian reduction. A mathematical model is established based on the particle swarm optimization to determine the first-order parameters of the paraxial design. Then, the model is optimized by iteratively updating a candidate solution with regard to a specific merit function that characterizes the zoom ratio, compactness, and aberration terms. In the optimization phase, the physical feasibility is considered as the constraint on the candidate solutions. Using two examples, this work demonstrates that the developed method is an efficient and practical tool for finding a realizable initial configuration of a dual-conjugate zoom system. Since this method is no longer reliant on the traditional trial-and-error technique, it is an important step toward the automatic design of complex optical systems using artificial intelligence.
ABSTRACT
Zernike polynomials provide an excellent metric basis for characterizing the wavefront aberrations of human eyes and optical systems. Since the Zernike expansion is dependent on the size, position, and orientation of the pupil in which the function is defined, it is often necessary to transform the Zernike coefficients between different pupils. An analytic method of transforming the Zernike coefficients for scaled, rotated, and translated pupils is proposed in this paper. The normalized coordinate transformation functions between the polar coordinates of the transformed pupil and the Cartesian coordinates of the original pupil are given. Based on the Cartesian and polar representations of Zernike polynomials, the coefficients' transformation matrix can be derived directly and conveniently. The first 36 terms of standard Zernike polynomials are used to validate the proposed method. For different types of transformation, transformation rules of individual Zernike terms are systematically analyzed, revealing how individual terms of the original pupil transform into terms of the transformed pupil. Numerical examples are presented to demonstrate the validity of the proposed method. Further application of the proposed method to the alignment of pupil-decentered off-axis optical systems is discussed.
Subject(s)
Computer Simulation , Image Enhancement/methods , Optical Phenomena , Pupil , Algorithms , Humans , Image Interpretation, Computer-Assisted/methods , Visual Perception/physiologyABSTRACT
Thermal control and temperature uniformity are important factors for aerial cameras. This paper describes the problems with existing systems and introduces modifications. The modifications have improved the temperature uniformity from 12.8°C to 4.5°C, and they enable images to be obtained at atmospheric and low pressures (35.4 KPa). First, thermal optical analysis of the camera is performed by using the finite element analysis method. This modeled the effect of temperature level and temperature gradient on imaging. Based on the results of the analysis, the corresponding improvements to the thermal control measures are implemented to improve the temperature uniformity. The relationship between the temperature control mode and temperature uniformity is analyzed. The improved temperature field corresponding to the thermal optical analysis is studied. Taking into account that the convection will be affected by the low pressure, the paper analyzes the thermal control effect, and imaging results are obtained in low pressure. The experimental results corroborate the analyses.
