In this paper, using Preston hypothesis and CCOS removal model, analyzing removal function of the spherical polishing end is analyzed as Gaussian distribution, four schemes are proposed to design the robot optical spherical polishing end effector. Through the analysis and comparison of advantages and disadvantages, an optimal solution is obtained and a standardized design is carried out to realize the synthesis of revolution and rotation of the spherical polishing wheel. The design of the spherical polishing tool adopts bevel gear transmission, belt transmission and planetary gear structure. When the motor input is 200r/min, by adjusting the specifications of the pulley, the spherical polishing wheel can achieve a revolution speed of 60r/min and a rotation speed of 100~400r/min. After the design is completed, finite element analysis is performed on the important parts of the structure, and the designed structure meets the strength requirements.
This paper introduces the testing of annular hyperboloid mirror with 460mm diameter in the Cassegrain system. To improve the testing efficiency and meet the requirements of utilization, the study is carried out from three stages: precision grinding, precision polishing, and optical coating. In the precision grinding stage, the annular Zernike polynomial is used to fit the measured surface combining with the data measured from the coordinate measuring machine, so that it can facilitate the testing of the distribution of the surface shape deviation over the entire surface. During the precision polishing stage, a feasible Offner compensator is designed to achieve the goal of high-precision testing of the hyperboloid surface, with a measurement accuracy of RMS≤0.02λ. Also, 0.5-0.7μm and 3-5μm dual-band high reflectivity and high uniformity reflective coating is designed for the Cassegrain system requirements, the actual test reflectivity is 96.2%, which can meet the design requirements.
The Space-based multi-band astronomical Variable Objects Monitor (SVOM) project is a dedicated satellite developed at the cooperation of China and France, aim to make prompt multi-band observations of Gamma-Ray Bursts (GRBs), the afterglows and other high-energy transient astronomical events. The Visible Telescope (VT) is one of the four payloads onboard the SVOM. VT is designed to observe the afterglows of GRBs both in the visible and near infrared bands simultaneously. The telescope can reach a limiting magnitude of +22.5Mv and provide the redshift indicators for high-Z (z<4) GRBs. VT is also designed to measure the Relative Performance Errors (RPEs) for the satellite attitude and orbit control system (AOCS), aiming to improve the pointing stability of the platform during observation. VT adopts a Ritchey-Chrétien (RC) catadioptric optical configuration with a 440mm aperture and uses the dichroic prism before the focal plane to split the incident light into blue (visible) and red (near infrared) band. Two Fine Guidance Sensor (FGS) CCDs are mounted beside the main CCD on the blue band focal plane of VT and provide sub-arcsecond pixel resolution. Fiber reinforced plastic (CFRP) composites is selected as the material of VT’s main structure to ensure enough stiffness and strength during launch. The electrical video processing circuit is carefully designed to make the readout noise below 6e-/pix (rms) in 100s exposure time. Active and passive thermal control are used together to ensure the optical performance and thermoelectric cooler (TEC) is adopted to control the main CCDs working temperature below -65°C to reduce the noise. This paper provides a comprehensive overview of the scientific requirements and the key instrument design aspects of optics, main structure, electrics, thermal control, performance test and validation results of VT.
Large aperture optical element deformed by its own weight is caused is one of the important considerations when we design the optical system, designing a mirror support solution that reduces the effects of gravity is critical. Traditional methods cannot effectively and intuitively analyze mirror distortion. In this paper, the finite element method and the optical surface fitting with Zernike polynomial are used to optimize the support scheme. These two methods are mutually verified and this method which use two parts is verified by the optimization scheme of the Φ900mm standard spherical mirror. With optimization, the steel belt loading and unloading weight hammer support scheme is finally adopted, and the best solution with Φ705mmin the circumference and each aperture is 55mm on the back of the mirror is obtained. The theoretical mirror surface’s PV and RMS value equal to 7.36nm (1/86λ) and 1.64nm (1/386λ), which is a good basis for guiding production.
This article, which is based on the topology optimization theory, considered the lightweight design of large aperture reflectors. Firstly, the material selection is based on the low temperature environment and the low temperature infrared optical mechanical structure design principles. Then, by using the minimum deformation of the mirror surface as the objective function, mirror volume and rigid body displacement as design restraints, and imposing manufacturing constraints, a conceptual design of the mirror back with manufacturability was accomplished. Finally, by using the finite element analysis method to compare the performance of the topologically optimized mirror and the primal mirror, it shows that the topologically optimized mirror met the design requirements in terms of lightening effect and structural rigidity, and the surface figure met the requirements under the influence of gravity, which emphasizes the feasibility and practicality of topology optimization in the large aperture mirror’ design.
With the development of the digital airborne photogrammetry technology, the more performances of the optical system for airborne mapping camera are required, such as the longer focal and the wider field of view (FOV). At the same time, the secondary spectrum correction becomes more important and difficult for the optical system design. A high performance optical system of airborne mapping camera with 200mm focus and 2ω=60° FOV is designed in this paper. The range of work wavelength is from 430nm to 885nm. A two-layer HDOE with negative dispersive characteristic is used to eliminate the secondary spectrum in the process of optical system design. The diffraction efficiency of the designed two-layer HDOE is up to 90%. From the result of design, the MTFs in whole fields are over 0.5 at 90lp/mm, which shows that the system has a great image quality. Meantime, the thermal analysis is done at the temperature range between -20°C and 40°C. As a result, MTF curves of the system at-20°C ~40°C show that a great image quality is kept, which meets the design requirements.
With the development of the digital airborne photo-grammetry technology, the more performances of the optical system for airborne mapping camera are required, such as the longer focal, the wider field of view (FOV), at the same time, the secondary spectrum correction becomes more important and difficult for the optical system design. A high performance optical system of airborne mapping camera with 200mm focus and2ω=60°FOV is designed in this paper. The range of work wavelength is from 430nm to 885nm. A two-layer HDOE with negative dispersive characteristic is used to eliminate the secondary spectrum in the process of optical system design. The diffraction efficiency of the designed two-layer HDOE is up to 90%. From the result of design, the MTFs in whole fields are over 0.5 at 90lp/mm, which shows that the system has a great image quality. Meantime, the thermal analysis is done at the temperature range between -20°C and 40°C, and the MTF curves of the system at-20°C ~40°C show that a great image quality is kept, which meets the design requirements.
Bad pixels and response non-uniformity are the primary obstacles when IRFPA is used in different thermal imaging systems. The bad pixels of IRFPA include fixed bad pixels and random bad pixels. The former is caused by material or manufacture defect and their positions are always fixed, the latter is caused by temperature drift and their positions are always changing. Traditional radiometric calibration-based bad pixel detection and compensation algorithm is only valid to the fixed bad pixels. Scene-based bad pixel correction algorithm is the effective way to eliminate these two kinds of bad pixels. Currently, the most used scene-based bad pixel correction algorithm is based on adaptive median filter (AMF). In this algorithm, bad pixels are regarded as image noise and then be replaced by filtered value. However, missed correction and false correction often happens when AMF is used to handle complex infrared scenes. To solve this problem, a new adaptive bad pixel correction algorithm based on pulse coupled neural networks (PCNN) is proposed. Potential bad pixels are detected by PCNN in the first step, then image sequences are used periodically to confirm the real bad pixels and exclude the false one, finally bad pixels are replaced by the filtered result. With the real infrared images obtained from a camera, the experiment results show the effectiveness of the proposed algorithm.
This paper designs a compact apochromatic lens with long focal length, which operates over very-broad spectrum from 400nm to 900nm for high resolution image application. The focal length is 290mm, and F-number is 4.5.In order to match CCD sensor, lens resolution must be higher than 100lp/mm. It is a significant challenge to correct secondary spectrum over very-broad spectrum for this application. The paper firstly pays much attention on dispersion characteristic of optical materials over this very-broad spectrum, and dispersion characteristic of glasses is analyzed. After properly glasses combinations and optimal lens structure selected, this compact apochromatic lens is designed. The lens described in this paper comprises fewer lenses, most of them are ordinary optical materials, and only one special flint type TF3 with anomalous dispersion properties is used for secondary spectrum correction. Finally, the paper shows MTF and aberration curve for performance evaluation. It can be seen that MTF of the designed lens nearly reach diffraction limit at Nyquist frequency 100lp/mm, and residual secondary spectrum is greatly reduced to less than 0.03mm (in the lines 550nm and 787.5nm). The overall length of this compact apochromatic lens is just 0.76 times its focal length, and because of fewer lenses and ordinary optical materials widely used, production cost is also greatly reduced.
Intensified CCD (ICCD) imagers have been widely used in low light level imaging system. While the ICCD has
smaller dynamic range in ubiquity, and its output image is prone to saturation in high light level. In this paper, the
auto-gated power supply method is put forward to implementing automatic brightness control (ABC). Consequently, the
ICCD camera imaging dynamic range is improved. Firstly, the principle of the auto-gated power supply is described
briefly, and the design scheme is carried out in detail. The pulse power control mode is adopted to the photocathode
instead of the traditional high voltage DC power supply, and the analog adjustment mode is adopted to the micro
channel plate (MCP). Secondly, an imaging experiment for ICCD camera was made to validate the auto-gated power
supply design, and the experiment results are presented. The results indicated that the design is valid, and the auto-gated
power supply method helps to improve the image quality of the ICCD camera. Finally, the key problems in the design
are analyzed and summarized in detail.
Image intensifiers are always used to amplify low light level (LLL) images in a wide wavelength range to observable
levels. As a leader in image intensifiers for industrial and scientific applications, intensified CCD (ICCD) is an
innovative product which is a hybrid of image intensifier and CCD. Over the past few decades ICCDs have been
increasingly developed and widely used in a variety of fields such as LLL television system and medical diagnostics. In
this paper, we present the application of ICCD in the field of LLL remote sensing. General LLL imaging devices are
introduced briefly, and their advantages and disadvantages are compared. ICCD technology which includes fundamental,
configuration and development, is expatiated on. The major parameters which incarnate the performance of the LLL
remote sensing ICCD camera are analyzed in detail, such as signal noise ratio (SNR), dynamic range, spatial resolution,
etc. An ICCD camera is designed, and an imaging experiment is made to validate the imaging ability of it in LLL
condition. The experiment results are discussed and summarized. At last, the most important issues to the application of
ICCD in LLL remote sensing are generalized in detail.
In this paper, a novel feature extraction method for palmprint recognition termed as Two-dimensional Combined
Discriminant Analysis (2DCDA) is proposed. By connecting the adjacent rows of a image sequentially, the obtained new
covariance matrices contain the useful information among local geometry structures in the image, which is eliminated by
2DLDA. In this way, 2DCDA combines LDA and 2DLDA for a promising recognition accuracy, but the number of
coefficients of its projection matrix is lower than that of other two-dimensional methods. Experimental results on the
CASIA palmprint database demonstrate the effectiveness of the proposed method.