2021 Vol. 42, No. 2
Taking high static low dynamic stiffness (HSLDS) vibration isolator with rhombic negative stiffness mechanism (rhombic HSLDS isolator) as research object, the equivalent friction model of negative stiffness mechanism was established by virtual work method, and the kinetic equation with factors of negative stiffness mechanism mass and friction was established by Lagrange method. The kinetic equation was solved by harmonic balance method (HBM), the influences of negative stiffness mechanism mass and friction on vibration isolation and optimization measures were analyzed, and the rationality of theoretical model was verified by the prototype. The experimental results show that the mass and friction of negative stiffness mechanism have adverse effect on vibration isolation and should be reduced. Connecting the shorter rod side of negative stiffness mechanism to the end of load platform can reduce influence of the negative stiffness mechanism mass on vibration isolation performance in higher-frequency range. Under condition that stiffness parameters of isolator and contact parameters of hinged pairs are fixed, and the stiffness and friction are satisfied simultaneously, the vibration isolation performance in low-frequency range can be optimized by increasing the rod length difference, and can reduce the influence of negative stiffness mechanism friction on vibration isolation in high-frequency range.
A new flexible support system was designed for the rectangular collimator of extremely large telescope. The system was a side support structure supported by six hollow cylindrical bars. The structural parameters and position parameters of flexible support system were optimized by multi-objective optimization algorithm, and the stability of the optimized flexible support system was also studied. The optimized flexible support system for collimator had a maximum peak valley (PV) value of 168.23 nm, root-mean-square (RMS) value of 30.306 nm and a weight of 229.21 kg under the influence of gravity only, which satisfied the design requirements. When the ambient temperature changed within 20℃~23.7℃, the mirror performance would not be affected; besides, random ground vibration would not affect the performance of the collimator and destroy the support structure. The results show that the multi-objective optimization design of the flexible support mechanism for collimating mirror comprehensively considers the coupling problems between the shape parameters of the flexible support mechanism for collimating mirror, the safety and reliability of the mechanism and the deformation of the optical surface, etc. Designers can choose the most satisfactory solution on the global scale as needed, which will greatly reduce the development cost and cycle time.
Security and protection surveillance lens is becoming more and more important in protecting personal and property safety, among which the pinhole lens is widely used because of its special structure. A pinhole lens was designed by using ZEMAX software for special occasions such as police forensics, reconnaissance, anti-terrorism as well as high temperature furnace and industrial inspection, etc. Aiming at the asymmetric optical system with the diaphragm in front of, the geometrical aberrations such as astigmatism, field curvature and distortion were controlled to optimize the design. The F number of the designed lens is 2 and the focal length is 6 mm. The lens matches 1/4 inch CCD, and the working spectrum is the visible light band, with the full field MTF≥0.48 at space frequency 100 lp/mm and the distortion ≤±3%. The designed structure is simple, which adopts the standard spherical design. The optical total length is less than 22 mm, which means better processing technology and low production cost. The tolerance analysis of the lens was analyzed, and the results show that the optical system has reasonable tolerances, good overall performance, and is feasible for mass production.
In order to meet the application requirements of high resolution and large detection range in thermal imaging field, based on the theory of mechanical positive compensation zoom, an objective lens with the long focal length was used as the prototype and a floating diaphragm structure was adopted, and a long-wave infrared imaging system with high-resolution and high-rate was designed. The primary parameters of this system include F-number of 1.2, zoom ratio of 40×, focal length ranging from 5.86 mm to 234.76 mm, and athermalization temperature ranging from −40 ℃ to 60 ℃, which is adapted to the long-wave infrared focal plane detector with the pixel size of 12 μm.
First, based on the aberration theory of the plane symmetric grating reflector system, the wave aberration of the imaging beam was corrected according to the optics material refractive index, and the aberration theory was extended to the plane symmetric refractive optical system, which made this theory can be applied to the aberration calculation of the catadioptric combined optical system with beam oblique incidence. Secondly, it was pointed out the computational expressions of wavefront aberration should be kept uniformed in view of the refractive index relationship between object and image spaces and the definition of direction of incident angle. Finally, the analysis and calculation were carried out on the aberration of the catadioptric ellipsoid mirror shape detection optical system by applying the extended aberration theory, and compared with the Zemax ray-tracing results to verify the effectiveness of the wave aberration theory. This aberration theory provides effective measures for the design of the catadioptric combined optical system with beam oblique incidence, the evaluation and optimization of image quality.
Aiming at the typical optical phased array, a set of silicon-based optical phased array chip performance evaluation methods were established to provide reliable data support for the optimal design of optical phased arrays. By designing a Fourier imaging system, the optical phased array could be dynamically imaged, and simultaneous observation of near-field and far-field imaging could be achieved. On this basis, a calibration scheme was designed to optimize the initial phase of the phased array. At the same time, the characteristic parameters such as scanning speed, angle and accuracy were analyzed from theoretical derivation and simulation to the structural design of the test system.
The spectral data of continuous spatial distribution can be obtained by the spaceborne spectrometer, which is widely applied in the detection of terrestrial vegetation and marine environment. In order to correct the distortion of the system, the imaging lens was designed as an off-axis transmission-type optical system. There were three optical axes in the system, the angle between the axes was 0.606°, and the eccentricity was 0.279 mm, which the traditional assembly and adjustment method could not solve this problem. The sensitivity analysis results of the system were obtained by using the computer-assisted assembly and adjustment technology, and a new assembly and adjustment method of multi-reference axis centring was proposed. The reference axis was constructed by presetting the eccentricity and tilt of the structure, and the reference axis was extracted by using an optical plate. The complex multi-axis system was decomposed into the single-axis subsystem, and the multi-axis transmission system assembly and adjustment of the spectrometer was accomplished. The test results show that the lens eccentricity error is less than 25.4 μm, the tilt error is less than 17.7″, and the distortion deviation between test results and theoretical results is less than 0.32 μm, which provides a new way for assembly and adjustment of off-axis refraction lens.
The circular hole workpiece is widely used in aerospace and other precision manufacturing fields. Rapid and accurate detection of the inner wall image of the circular hole is an important means to ensure the quality of the workpiece. An image detection method of inner wall of circular hole workpiece based on 45° reflector was introduced. In this method, the sectional image of the inner wall was obtained by inserting the reflector into the workpiece, and the complete image of the inner wall was obtained by continuous rotation of the workpiece and image stitching ways. A 45° reflector was designed and manufactured for a workpiece with 4.5 mm inner diameter, and the effective imaging area as well as the influence of translation and tilt errors were analyzed theoretically. A measuring device for the inner wall of circular hole workpiece was built, and a special calibration workpiece was designed and manufactured to realize the calibration of pixel equivalent of the measuring device. The experimental results show that the system pixel equivalent is about 5 mm, the measurement relative error is less than 3.5%. The effective imaging area of a single image is obviously improved, and the complete image of the inner wall of the workpiece is obtained by the stitching method.
Aiming at the condition that the imaging object does not exceed the memory effect range of the scattering medium, a method combining digital off-axis holography to reduce the speckle autocorrelation noise in the imaging of the scattering medium was proposed. When the imaging target passed through the scattering medium, the autocorrelation technique combined with the phase recovery algorithm could reconstruct the imaging target from the speckle. However, in the actual imaging process, in order to effectively suppress the influence of environmental noise and thermal noise on the reconstruction effect, the design used the phase shift method in off-axis holography to eliminate the interference of the static noise item in the noise item, and then used the speckle autocorrelation and the phase recovery algorithm reconstructed the imaging target with better effect after denoising. The structural similarity was used to quantitatively evaluate the reconstruction effect. The simulation results show that for the given imaging target, the structural similarity before and after denoising increases from 0.879 6 to 0.987 5, which verifies the effectiveness of the method. It shows that the proposed method can improve the reconstruction effect of speckle autocorrelation method.
The hatched egg embryo is the carrier for the production of avian influenza vaccine. The activity detection of the egg embryo is a key link in the production of vaccine. The detection of the egg embryo activity by the photoelectric volume pulse method is the key to improve the accuracy of the egg embryo activity detection rate. In order to improve the detection efficiency and accuracy of egg embryo activity, the sliding power spectrum method was adopted to visualize egg embryo pulse wave, which accurately classified egg embryo activity based on convolutional neural network. The experimental results show that the calculation time of a single egg embryo signal using a convolutional neural network is only 12.6 ms, and the detection efficiency is increased by nearly 200 times in comparison with the manual detection method. The convolutional neural network classification accuracy of the visualized egg embryo pulse wave can reach 94.14%, among which the true positives of live embryos, dead embryos and weak embryos are 99.74%, 93.73%, and 84.39%, respectively. The egg embryo activity classification model based on the convolutional neural network can accurately identify the egg embryo activity in large-scale production, which has important application value for the vaccine production process.
A recognition technology of two-dimensional code was proposed with an effective and accurate way for industrial applications, and the identification system for a batch of two-dimensional code with high speed based on machine vision was developed. Firstly, a method of locating the region of interest in each two-dimensional code with batch processing was proposed according to the geometric relationship between the measured two-dimensional code and the target subspace. Then, the anti-noise ability of the system was evaluated by adding Gaussian noise in the images, which simulated the noise produced in the actual process. Finally, the relationship between the recognition rate in the system and the motion speed of the two-dimensional code was analyzed, and the experimental results with references were compared. The results indicate that the average recognition time of each two-dimensional code is 17.8 ms with noiseless images and is 21.3 ms with noise images respectively in the test data set of 1 800 sheets with the motion speed of 296.8 mm/s, and the recognition rate is 100%. The system meets the online detection requirements.
To solve the loss of image details when removing the stripe noise of hyperspectral images (HSI), a destriping method for hyperspectral images was proposed, which was based on the weighted block sparsity (WBS) regularization and the minimax concave penalty (MCP) constraint (WBS-MCP). WBS-MCP was constructed by employing weighted ℓ2,1 norm and MCP norm for the sparse features and low-rank constraints, and applying ℓ1 norm to the edge smoothing constraint of clean image. The alternating direction method of multipliers (ADMM) algorithm was used to iteratively solve the corresponding constraint model, and the clean HSI image was obtained by reconstruction. The experimental results show that the mean equivalent number of look of real HSI improves from 28.45 to 83.47, and the edge retention index increased by 0.056 at least, especially for the aperiodic stripe noise. The adaptive weight was used to update the sparse level, which could enhance the group sparsity and has better performance in maintaining the image edge and enhancing the area smoothness, so that the noise removal has better effect on aperiodic stripe noise.
Nowadays, the infrared imaging technology is widely used in space detection, land inspection, security monitoring and other fields. In order to ensure the accuracy of the infrared target recognition, it is necessary to completely understand the radiation characteristics of the target. The target radiation characteristics need to be measured in out-field condition, and the large area blackbody radiation source need to be used for field radiation parameters calibration to the measuring equipment of target characteristics. A large area blackbody radiation source was designed. The radiator was made of aluminum material with black treatment, and the proportion integral differential (PID) control algorithm was adopted by the temperature control of large area blackbody radiation source. When the actual ambient temperature was 26.8 ℃ and the humidity was 60%, the radiation parameters of the target characteristics measuring equipment were calibrated. The test data show that the uncertainty of the radiation temperature measurement is 0.4 ℃ ( k = 2), and good application effect is achieved.
In the grinding stage of large-aperture aspheric mirror, the geometric parameters should be measured accurately, and the surface shape should also meet certain accuracy requirements. By means of numerical simulation of the test process, the accuracy of measuring geometric parameters and surface shape using three-coordinate measuring machine (3-CMM) and laser tracker was evaluated. An effective contour detection method was proposed to meet the requirements of the detection index of a 2 m-aperture parabolic mirror. Four laser trackers were used to build a multilateral measurement system, the Levenberg_Marquardt algorithm was used to calibrate the system, the new target ball was used to realize the synchronous and rapid acquisition of mirror points by multiple trackers, and the test data were adjusted and coordinate system transformation was processed. Finally, the geometric parameters and surface shape were obtained. After grinding, the 2 m-aperture parabolic mirror was tested. The errors of vertex curvature radius, aspheric coefficient and surface shape RMS are 0.16 mm, 0.000 6 and 1.06 μm, respectively.
An defect detection method of micro-cantilever beams based on optical coherence vibrometer (OCV) system was proposed. The maximum vibration displacement measuring range and vibration frequency of the home-made OCV system were 2.574 mm and 138.5 kHz, respectively. This system was used to carry out the vibration measurement of the defective micro-cantilever beams with additional mass-block coupled structure, and its natural frequencies were obtained. Subsequently, the defect location was realized by using the influencing characteristic of the additional mass-block on natural frequencies. In the process of processing the interference spectrum signals collected by the system, the fast Fourier transform (FFT) and Fourier transform (FT) refinement spectrum correction algorithm was utilized for error correction, and the accuracy could be increased by more than 1 000 times, which enabled the system to realize the displacement measurement at nanometer scale. The experimental results show that this method can identify the defect location of micro-cantilever beams effectively, which provides a new method for the defect detection of micro structures and expands the application of optical coherence vibrometer technology in nondestructive testing of engineering structures.
Although current commercial spectrometer can measure and analyze the detecting targets in extremely high spectral resolution, it still suffers from many disadvantages such as complicated system, bulky size and expensive costs, which are difficult to meet the needs of field testing. In order to solve these problems, a portable multi-channel spectral measurement system for rapid on-site detection was designed. Compared to the traditional spectrometer, the proposed design was not only compact, but also had rather high spectral resolution; and additionally, its multi-channel configuration supported simultaneous detection for multiple samples to further improve the sensing efficiency. Proved by the detecting results on Rhodamine 6G and avian influenza virus H7N9 antibodies, the proposed portable multi-channel spectral measurement system could quantitatively measure various samples in high accuracy. Because this system has the advantages of good sensitivity, high resolution and small volume, it is expected to be used in the rapid on-site spectral detection application.
In order to measure the cell traction more quickly and intuitively, a measurement method based on Fourier transform was proposed. Firstly, the two-dimensional fast Fourier transform was applied to the image of the micro-column array to obtain its spatial spectrum. Then, one spot in the first-order diffraction spot was selected for the fast Fourier transform to obtain the amplitude distribution of the micro-column array. Finally, the distribution of the offset of the micro-column array could be obtained from the distribution of amplitude mutation and the severity of mutation, and then the distribution of cell force could be obtained by multiplying the stiffness of the micro-column. The influence of frequency point selection, filter window size and offset point size on the experimental results was investigated through simulation experiments. On this basis, the high-power micrograph of cell micro-column was measured. The experimental results show that this method is comparable to the centroid method in terms of the result presentation. The relative error of the maximum cell force measured in each region is within 17.37%, the relative error of the average cell force measured in each region is within 7.93%, and the operation speed is nearly 10 times faster than that of the centroid method.
Surface defects seriously affect the quality and service life of bearings. In recent years, deep learning has played an important role in defects detection, but for bearing detection, the collection of defects samples is time-consuming and labor-consuming. The bearing inner diameter was chosen as the detection object, a method of standardized sample split based on the symmetry of bearing was proposed, which could greatly increase the number of samples. Different sample processing methods were used respectively, and then the bearing defects detection model was trained by ResNet network to carry out several comparative experiments. The experimental results show that the detection effect is worse when the original images are directly used for training, and the area under the curve (AUC) of the model is only 0.558 0; after the samples are split, the trained model detection effect is better, and the model AUC is improved to 0.632 6; after the samples are corrected by four point perspective transformation, the detection effect is better, and the model AUC is increased to 0.661 3; after the original images are corrected by perspective transformation and the standardized samples are split, the detection effect is the best, and the model AUC is increased to 0.849 6.
The collimator is a commonly used optical precision instrument in optical laboratory, it simulates an infinite target by illuminating the target with the light source, which is the necessary equipment for assembly, adjustment and testing of optical system. A collimator with 200 mm aperture and 5 000 mm focal length was designed and off-axis two-reflective system structure was used, and the field angle was 0.35°. Both primary and secondary mirrors were aspherical and the secondary mirror was convex double-curved surface. The design value of system center field-of-view wave aberration was 1/62 λ, and that of edge field-of-view wave aberration was 1/21 λ. The inspection scheme of secondary mirror of this collimator was studied, and a simple and reliable front testing scheme for convex double-curved surface secondary mirror was proposed.
As a new optical element, the liquid lens provides adjustable optical power by changing the curvature. The transmission wavefront quality of liquid lens will affect the imaging quality. In order to apply liquid lens to precise optical system, it is necessary to investigate its transmission wavefront characteristics. The variation of the optical path difference (OPD) with the curvature radius, and the sensitivity of the OPD to the optical power in different heights of incident light in liquid lens aperture were analyzed by theory and simulation, so as to study the uniformity of slight variation of OPD in pupil. The transmission wavefront of liquid lens in zero, positive and negative optical power was measured. The uniformity of OPD variation of liquid lens was verified by analyzing the experimental data. The experimental results show that the spatial maximum difference of optical path difference variation is about 0.22 λ~0.36 λ, and the dispersion degree of spatial distribution is about 0.01 λ~0.02 λ. The analysis results show that the OPD variation of liquid lens with respect to the minor variation of electrical current has good uniformity, which can provide support for application and aberration compensation of liquid lens in precise optical system.
It is of great value for the development of phototherapy equipment to improve the uniform distribution of illuminance on the irradiation plane of the light therapy light source composed of light emitting diodes (LED). An illuminance optimization method for phototherapy LED light source based on multi-objective artificial fish swarm algorithm was proposed, and designed two different combination modes of phototherapy LED light source array. Combined with multi-objective artificial fish swarm algorithm, the combination data of phototherapy LED light source array was optimized to make the illuminance distribution of phototherapy LED light source array more uniform. The optimized design of phototherapy LED light source chip combination data were imported into the optical simulation software TracePro to achieve simulation verification. The illuminance uniformity of the optimized circular light source arrangement is 0.104 higher than that of the un-optimized circular light source arrangement, and the illuminance uniformity of the rectangular light source arrangement is 0.148 higher than that of the un-optimized rectangular light source arrangement. By comparing and analyzing the final data, it shows that the optimization method is feasible and can improve the illuminance distribution level of phototherapy LED light source.
Through the finite element analysis of gyroscope fiber-optical ring under the linear acceleration field of spacecraft in large maneuvering motion, the deformation mechanism of the fiber-optical ring was obtained. Based on the theoretical knowledge of anisotropic materials, the micro-mechanics finite element method was used to apply periodic boundary conditions to the representative volume element (RVE) of the fiber-optical ring. Therefore, the equivalent material parameters of the fiber-optical ring were analyzed. The finite element program ANSYS was adopted to establish the spatial finite element model of the fiber-optical ring assembly and apply the acceleration field. The contact element was established to analyze the structural contact coupling effect during the deformation process. The analysis results show that the U-shaped structure and top cover of the fiber-optical ring assembly structure will contact with the fiber-optical ring after deformation under the action of acceleration field. In addition, the U-shaped structure and top cover structure will deform under the action of inertial force, which will affect the deformation of the fiber-optical ring.
In order to realize the measurement of resonance wavelength of plasma grating, and research the response sensitivity of grating parameters to stress, a new type of stress-sensitive polydimethylsiloxane (PDMS) thin films plasma grating was proposed. Based on the principle of finite-difference-time-domain (FDTD) method, a structural simulation model, that is periodic plasma grating model was constructed. With the help of periodic boundary conditions and applying the stress on the grating, the resonance wavelength was measured by changing the plasma grating parameters, such as period, duty cycle and Au film thickness, and the response sensitivity of grating parameters to stress was studied. Finally, the simulated results were compared with the theoretical values, and the relative error was obtained. The simulated results show that when the grating period is 0.7 μm, the duty cycle is 55%, and the gold film thickness is 0.02 μm, the response to stress is most sensitive. Secondly, the resonance wavelength at different periods obtained by simulation is compared with the theoretical value, and the results are consistent; when the period is 0.7 μm, the wavelength of the resonance peak is 1.251 μm, and the relative error obtained by simulated results and theoretical values is less than 2%, which means the results are more accurate. This method plays an important role in the fields of monochromator, spectrometer, sensor, and so on.