Chinese Version Light学术出版中心
Latest Issue
Issue 4 ， 2015
-
Al/MgF2 mirrors in vacuum ultraviolet region
Abstract：Al/MgF2 mirrors in vacuum ultraviolet region were developed by three step thermal boat evaporation method, and a method to improve the reflectivity of mirrors by fabrication technology was explored. There are three steps to fabricate the two layers Al/MgF2 mirrors. In the first step, an aluminum coating with a thickness about 70 nm was evaporated on a quartz substrate at the room temperature. And then, the MgF2 coating with a thickness about 10 nm was quickly evaporated on an aluminum coating. In the third step, the substrate was heated to certain temperature, and the MgF2 coating with a thickness of 15-20 nm was evaporated on the surface of the Al and MgF2 coatings. According to changes of the substrate temperatures at the room temperature, 100, 200 and 300 ℃, the effects of the substrate temperatures on the mirror reflectivity were researched. The results measured by a vacuum ultraviolet reflector show that improving the substrate temperature after evaporating MgF2 is in favour of increasing the reflectivity of Al/MgF2 mirror and the thickness of the Al/MgF2 is related to the reflectivity of the mirror. When the thickness of MgF2 is 26.7 nm, the reflectivity at 122 nm is about 85%. The reflectivity of the mirrors stored in the laboratory is barely changed after one month and five months. The results provide technological function for higher performance optical elements in vacuum ultraviolet optical systems.Keywords：vacuum ultraviolet mirror;Al/MgF2 mirror;substrate temperature;reflectivity- 47
- |
- 9
- |
- 2
Published：2020-08-13 -
Application of optical fiber Bragg grating strain gauge to cable force monitoring of FAST
Abstract：To monitor the cable force of the cable-net supporting structure of the Five-hundred-meter Aperture Spherical radio Telescope( FAST) and to avoid the effect of traditional measuring methods on the cable-net supporting structure and the electromagnetic interference, this paper presents a method to obtain the cable force values indirectly. The method uses Fiber Bragg Grating(FBG) sensors to monitor the cable connector strain to measure the cable force indirectly. In the measurement, a FBG strain gauge was installed at the linear strain region of the cable connector axially by using a dedicated welded base, by which the adverse effect of welding directly on the performance of cable connector structure was avoided. A temperature compensation method was used to compensate the effect of temperature changes on the FBG stain gauge measurement. The correlation coefficients were acquired by the calibration of the cable prestressing process. The cable force monitored then was calculated from the calibrated relation in actual engineering applications. Test results indicate that the fitting linearity of the cable force and the cable connector strain is up to 0.98 and the Root Mean Square (RMS) error in practical measurement is 1.38 t. The relative error is better than 3% within the range of the cable force for the FAST. The method is characterized by no electromagnetic interference, simple wiring, good reliability and long duration. It has been successfully applied to the cable force monitoring of 316 typical cables of the supporting cable-net in the FAST project.Keywords：Fiber Bragg Grating(FBG);strain gauge;cable force monitoring;temperature compensation;radio telescope- 76
- |
- 12
- |
- 6
Published：2020-08-13 -
Control of correlated color temperature for multi-primary color LED illumination
Abstract：Based on the established photo-electro-thermal (PET) model, a model predictive control method of Correlated Color Temperature(CCT) for a Light Emission Diode(LED) was investigated to realize the CCT control of multi-primary color LEDs. The Guassian distribution hypothesis and the thermal equilibrium variable relationship stability hypothesis were presented. The regression sub-models of different model parameters were calculated by least square estimation method successively according to the strategy of soft model. The change trend of spectral sensitive coefficient curves with different CCT curves was analyzed. Then, current control parameter values of 3 typical CCTs at 3 000, 4 500 and 6 500 K were fixed by the gravity line adjusted method. Finally, a set of spectral power distribution curves were obtained by bringing a certainty random variation to the fixed current control parameter values to validate and evaluate the accuracy of the PET model. Experimental results indicate that the PET model predicts accurately the heat sink temperature and the Spectral Power Density(SPD) of the LED by control of the currents and environment temperatures, the accuracy of predictive chromatic coordinate value is better than ±0.005, and the accuracy of predictive CCT is better than ±150 K. The model-based control method has good accuracy for CCT control and can be generalized to the multi-primary color LED illumination with more primary color channels.Keywords：illumination source;multi-primary color Light Emission Diode(LED);correlated color temperature;photo-electro-thermal model- 71
- |
- 12
- |
- 8
Published：2020-08-13 -
Mechanical error compensation algorithm for subaperture stitching interferometry
Abstract：An error compensation algorithm was proposed by introducing a position correction compensator into general stitching algorithm to reduce the relative location errors between subapertures due to poor positioning accuracy in a subaperture stitching interferometry. The working principle of the algorithm was introduced and the accuracy of the fitted translation and rotation coefficients was analyzed in theory. Then a simulation experiment by using MetroPro software and Matlab software was implemented, and the influence of positioning accuracy on the stitching results was analyzed. The simulation result shows that the accuracy of rotation coefficient is less than that of the translation coefficient and is consistent with the theoretical analysis. Moreover, the algorithm is more robust than the general stitching algorithms. For the purpose of experimental verifying mechanical error compensation algorithm, a Φ150 mm flat mirror was tested by a subaperture stitching interferometer and a full aperture interferometer. The test results indicate that the peak-to-valley(PV) and root-mean-square(RMS) of the phase distribution residue are 0.015 30λ and 0.001 570λ, respectively as compared with the stitching results from the directly measured full aperture, which means that the optimal algorithm is stable and reliable and effectively compensates positioning system errors.Keywords：stitching interferometry;subaperture stitching;positioning system error;compensation algorithm;large aperture flat mirror- 62
- |
- 11
- |
- 6
Published：2020-08-13 -
Position matching of dynamic shaft surface based on digital speckle correlation
Abstract：As the rotating movement in dynamic torque measurement will prevent the strain measurement directly, a position matching method for the dynamic shaft surface was proposed based on the digital image correlation method. The method recognizes the position of shaft surface in rotating movement to calculate its strain displacement. An digital image correlation experimental system for the movement shaft surface was set up, and a calibration experiment to determine the angle ranges of shaft surface with stable grey values, a measurement experiment of standard angle displacement, and an identification experiment for the position of dynamic shaft surface were set up, respectively. Experiments show that the grey value is stable when the angle range is -π/15-π/15, in which the obvious correlation peak has been extended to 160 pixels in the rotational direction. The relevance is respectively 0.389 2 and 0.322 1 when the angels are -π/15 and π/15. Out of which, the image gray gradation information is submerged in the noise caused by the changes of shaft radians. Moreover, both the precisions of standard rotation-deflection and dynamic position of the shaft surface are 1 pixel. The method solves the problem on position matching of the dynamic shaft surface and also provides an effective method for measuring the strain and displacement of the dynamic shaft.Keywords：digital speckle correlation;digital image correlation;reference image sequence;dynamic shaft surface;position matching- 59
- |
- 8
- |
- 1
Published：2020-08-13 -
Automatic alignment of multiplexed beams of excimer laser system based on fluorescence imaging
Abstract：The multiplexed beam automatic alignment of a Master Oscillator Power Amplifier(MOPA) system in a high power excimer laser based on scattering imaging was explored to achieve the multi-pass amplifications of amplifiers and high pointing accuracy of a target. A 325 nm He-Cd laser was selected as an automatic alignment source in the whole optical path. Then a complex imaging collection system was proposed by combining the photosensitive paper synchronized reception and a CCD visible imaging to complete the near-field and far-field scattering imaging in the automatic alignment system. Meanwhile, the information processing software was compiled based on the image region segmentation to accomplish the closed loop feedback control for automatic alignment of several array beams. Finally, image collection validation experiments for pre-amplifier beam automatic alignment were carried out. The results indicate that the light intensity tunable multiple value of the scattering imaging system is 300, the ratio of the error of automatic alignment beams on the amplifier windows and the window diameters is lower than the designed value by 1.08% and the total time of automatic alignment of the three beams is 40 s, which satisfies the demands of the amplifier for geometric fill and energy extraction.Keywords：Excimer laser;Master Oscillator Power Amplifier(MOPA);beam alignment;automatic alignment;fluorescence imaging;region segmentation;tunable amplification- 86
- |
- 10
- |
- 3
Published：2020-08-13 -
Strain sensor based on coaxial photonic band gap crystal
Abstract：According to microwave network theory, a coaxial photonic band gap crystal strain sensor was proposed based on a variable insulating layer. The model of the coaxial photonic band-gap crystal sensor was provided, and the relationship between the peak frequency of band gap and the electric length of the crystal was deduced. The structural size and the material parameters of the coaxial photonic band gap crystal sensor under a certain demand were designed. The S parameters were calculated, and they are well coincided with that from a simulation. The method for improving the sensitivity and quality factor of the sensor was analyzed and an experimental platform was set up. The experimental result shows that when the strain changes from 0 με to 10 000 με, the peak frequency of the band gap is changed from 2.450 GHz to 2.432 GHz, in which the frequency shift is 18 MHz, and the sensitivity is 1.8 kHz/με. The simulation results coincide with the experimental one, and validate the feasibility of the designing method of the strain sensor.Keywords：coaxial photonic band gap crystal;strain sensor;variable insulating layer;characteristic impedance- 63
- |
- 10
- |
- 2
Published：2020-08-13 -
Dual-order overlapped Offner imaging spectrometer in middle- and long- wave infrared regions
Abstract：An Offner imaging spectrometer based on Infrared Focal Plane Arrays(IR FPAs) operated in two common-path diffraction orders was proposed to extend the spectrometer wavelength coverage. The overlapped rays from the first order and the second order of convex grating could be naturally separated and simultaneously detected by the dual-band IR FPAs on the focal plane. The basic principles and design cautions were discussed in detail. Through geometrical ray tracing, the spectral smile and keystone were evaluated. Based on Huygens Point Spread Function(PSF), the Spectral Response Function (SRF) was also simulated, from which the spectral bandpass was derived as well. The dual-band Offner imaging spectrometer covers the wavelength range of 3 to 6 μm in the second order and 6 to 12 μm in the first order with bandpasses of 13.2-14.3 nm and 28.3-33.3 nm respectively. The two diffraction orders have the same spectral smile and keystone characteristics by both within half of a pixel width. The grating efficiencies are not lower than 20% over the full wavelength ranges. For its compact construction and wide spectral coverage, the instrument is competent for the measurements of the earth surface or deep space objects in the middle- and long- wave infrared (MWIR/LWIR) regions with moderate resolutions.Keywords：imaging spectrometer;dual-order overlapped;common-path detection;dual-band IR Focal Plane Array(FPA)- 61
- |
- 16
- |
- 7
Published：2020-08-13 -
Surface testing with phase diversity method
Abstract：To verify the demonstration system of a phase difference wavefront detector by using its own light source to complete the wavefront detection independently, an experiment platform to detect the mirror surface shape with the phase diversity method is set up. The phase diversity method collects shorter exposure images in the focal plane and away from the focal plane at the same time, then it calculates the distribution of wavefront solutions and recovers the target based on known defocus, so as to realize the estimation of large mirror aberration. In order to further validate the phase diversity method, the measurement results from phase diversity method are compared with that from a high accuracy ZYGO interferometer. Experimental results demonstrate that the error distribution, PV values and RMS values of the two methods are well in agreement, and their wavefront RMS accuracy is 2.83/1 000λ. These results mean that the phase diversity method effectively detects the mirror aberration and has good feasibility and accuracy.Keywords：mirror surface;surface test;phase diversity method;Zernike polynomial;Aberration- 48
- |
- 10
- |
- 1
Published：2020-08-13 -
Control system for 980 nm high stability laser pump source
Abstract：A high stable control system for a 980 nm laser pump source was designed and fabricated to Er- doped optical fiber amplifiers for their stable operations. Firstly, a drive unit of the control system was designed based on the principle of a constant current excitation. Followed that, a temperature control unit of the control system was designed by using a Thermoelectric Cooler (TEC) as the measure of temperature control. Then, a complete laser pump source was assembled to verify the effectiveness of the control system. Finally, the output characteristics of the laser pump source was investigated experimentally including the relation between light power and driving current, and the stability of optical power and spectrum. The corresponding tests were performed, and results show that the center wavelength of the laser pump source is 975.2 nm, the optical power reaches 600 mW, and the power stabilities in a short-term and a long-term are ± 0.008 dB and ± 0.05 dB, respectively. As compared with the similar laser pump source, it has a high stability. It indicates that the laser pump source with the designed control system meets the design requirements, and has a certain practical value.Keywords：laser pump source;laser pump control system;constant-current source;semiconductor temperature control;Er-doped Fiber Amplifier(EDFA)- 44
- |
- 11
- |
- 8
Published：2020-08-13 -
Laminated fabrication of micro-mold based on WEDM and thermal diffusion welding
Abstract：A 3D micro-structure with a high aspect ratio was fabricated by combining Wire Electrical Discharge Machining(WEDM) and vacuum pressure thermal diffusion welding. The WEDM and thermal diffusion welding were researched, and the better technological parameters were obtained to fabricate a micro-mold. Firstly, a copper foil with a thickness of 100 μm was cut to obtain a multi-layer 2D micro-structure under the conditions of a pulse width of 10 μs, a pulse interval of 40 μs, a wire cutting current of 0.28 A and a voltage of 60 V. Then, the 2D micro-structure of a multilayer copper foil was fabricated by vacuum pressure thermal diffusion welding under the technological parameters in a thermal diffusion temperature of 850°C, a thermal diffusion time of 10 h and a pressure of 1.0 μPa. The multilayer copper 2D microstructure was connected together by vacuum pressure thermal diffusion welding to fit into a six frustum pyramid mold and gear molds with two-stage steps and three-stage steps, respectively. Experimental results indicate that the 3D micro-mold with good surface quality is an ideal fabrication and fits to design models. Finally, based on ultrasonic powder molding, two-stage and three-stage plastic gears are respectively obtained. These micro plastic parts show good quality, which verifies the feasibility and usability of laminated micro molds.Keywords：3D micro-structure;micro-injection mold;Wire Electrical Discharge Mechining(WEDM);vacuum pressure thermal diffusion welding- 42
- |
- 9
- |
- 2
Published：2020-08-13 -
Mechanical dressing of resin bond diamond grinding wheel based on dressing force
Abstract：The relationship between dressing force and dressing effect in resin bond diamond grinding wheel processing was researched. The topography and the grinding performance of a grinding wheel were characterized by the variation of dressing forces. Firstly, the dressing experiments for resin bond diamond grinding wheel were performed by using boron carbides, silicon carbides and the corundum, and the variation of dressing forces was collected. Then the topography of dressed grinding wheel was observed by a white light interferometer. Finally, the grinding tests were conducted to obtain the grinding performance. On the basis of the experiments above mentioned, the relationship between the variation of dressing forces and the topography of dressed grinding wheel was analyzed and verified. Experimental results show that the normal force Fn represents the cutting edge density and the protrusion of diamond abrasive, and the dressing ratio β reflects the sharpness of diamond abrasive. In addition, the dressing process is sufficient when β begins to stability. So the dressing forces are related to the topography and the grinding performance of grinding wheels, and the dressing processing is controlled based on the variation of dressing forces.Keywords：grinding;mechanical dressing;resin bond diamond grinding wheel;dressing force;Topography- 59
- |
- 11
- |
- 4
Published：2020-08-13 -
PCB stator winding in axial flux permanent magnet motor for reaction flywheel system
Abstract：To meet the miniaturization requirements of a reaction flywheel for small satellites, a reaction flywheel system using the axial flux permanent magnet motor based on a Printed Circuit Board (PCB) stator was proposed and the winding layout form for the PCB stator winding was researched as well. According to the system design and manufacturing requirements, a combination of theoretical and finite element analysis was applied to the illustration of generating mechanism of the reverse torque in the spiral winding. The effects of spirally type and waveform type PCD stator windings on the flywheel system performance were also analyzed, respectively. Finally, the performance of flywheel system prototypes with two forms of stator windings was tested on the ground. The results indicate that the driven motor with the waveform PCB stator winding has reduced its power consumption by 26.2% than that with spirally winding when the flywheel works at a rated speed of 5 000 r/min, meanwhile its electromagnetic efficiency is also reduced by 0.8%. The experimental results verify the correctness of theoretical analysis and simulation results, and provides an important reference for the engineering applications of the axial flux permanent motors with PCB stator windings.Keywords：reaction flywheel;Printed Circuit Board (PCB) stator winding;axial flux permanent magnet motor;Finite Element Analysis (FEA)- 44
- |
- 10
- |
- 5
Published：2020-08-13 -
Simulation and test of three-frequency piezoelectric bone conduction hearing device
Abstract：A three-frequency piezoelectric bone conduction hearing aid device was proposed. The device adopts three piezoelectric vibrators with different sizes to converse the electrical signals into audio signals, which could adapt to a wide frequency range. The modal analysis and harmonic response simulation analysis of the vibrators were conducted, the best modes and resonance frequencies of the vibrators were selected, and their operating frequency bands were determined. A prototype for three-frequency piezoelectric bone conduction hearing aid devices was designed and manufactured according to the simulation results, and its amplitude-frequency characteristics and loudness were tested. The experiments show that the maximum vibration amplitudes of the low-frequency, mid-frequency and high-frequency piezoelectric vibrators are 86.08 μm, 34.24 μm and 1.545 μm, respectively, and they appear in their respective frequency bands. At their own response frequency band, every piezoelectric vibrator's loudness is largest and the maximun values are 69.1 dB, 98.3 dB and 117.1 dB, respectively. When three piezoelectric vibrators are working at their respective bands simultaneously, the sound in each frequency band could obtain very good response, which broadens the sound response frequency domain of the hearing device.Keywords：bone conduction hearing device;three-frequency type;piezoelectric vibrator;simulation- 57
- |
- 8
- |
- 1
Published：2020-08-13 -
Polishing pressure control system for large caliber aspherical optics
Abstract：According to the demands of large-caliber aspherical optical elements for polishing technology, a kind of dual pressure balanced polishing pressure control system was proposed based on the planet type rotational structure. The closed-loop pressure control system was built by using a low friction cylinder, two electrical proportional valves and several pressure sensors. The nonlinear mathematical model of the pressure control system was built by analyzing experimental values. In order to output a constant pressure, a composite controller was developed by combining with a feedforward control and multiple sets of bimodal PID controls. Experimental results show that the control system achieves grinding pressure smooth transition and implements stepless adjustment and flexible control for the polishing pressure. The output of the pressure is adjustable within the range 0 to 350 N and the steady pressure fluctuation is less than 1 N. The system has stroger robustness against the enough disturbances of a cylinder piston. The system basically meets the stability and accuracy requirements of the polishing pressure.Keywords：large caliber aspheric;optical polishing;polishing pressure;pressure control;PID control- 46
- |
- 9
- |
- 3
Published：2020-08-13 -
Support structure of primary mirror for small optical remote sensor
Abstract：An opto-mechanical structure for a microminiature optical remote sensor was designed to obtain favorable images under a wider temperature range and severe dynamic environments. The design principle and concrete realization method of the support structure of a primary mirror and the most critical core component in the whole opto-mechanical structure of the optical remote sensor was researched. The boundedness of traditional supporting way of a primary mirror was explored through analysis on the mechanical and thermal properties of primary mirror chamber in the initial designing scheme. Then, a new-style and flexure support structure suitable for a mini-style mirror was designed based on flexible support principle. The thermal adaptability and dynamics environment suitability of the support structure were analyzed by finite element method, which verifies that the flexible support structure could meet the design requirements. In the end, the processing and concrete implementing methods of the primary mirror chamber of the optical remote sensor were presented. The experiments of thermal shock test and partial test on the primary mirror were performed. The results show after thermal shock test, the primary mirror won't appear the crack phenomenon at -60 ℃ -80 ℃. Moreover, the surface figure accuracy RMS of the mirror remains a level of 0.025λ (λ=632.8 nm) in -20 ℃ to 50 ℃. These results demonstrate that the primary mirror design satisfies the application environment requirements of the optical remote sensor.Keywords：remote sensor;primary mirror;flexure support;Modal analysis;cold machining;electrical discharge machining- 63
- |
- 15
- |
- 9
Published：2020-08-13 -
Effect of triethanolamine in lapping spinel using fixed abrasive pad
Abstract：The action mechanism of triethanolamine in lapping spinel wafers using a fixed abrasive pad was investigated, and a serial of experiments were carried out. Firstly, micro indentation experiments were conducted to measure the hardnesses of spinel wafers soaked in triethanolamine solution and de-ionized water. Then an X-ray photoelectron spectrometer (XPS) was employed to analyze the chemical mechanism of triethanolamine and to research the changes of chemical composition on wafers' surface layer with etching depth increasing. Furthermore, the softened layer thicknesses affected by triethanolamine solution and de-ionized water were estimated. Finally, the influences of triethanolamine solution and de-ionized water on the material removal rate and surface quality were discussed by a lapping experiment using the fixed abrasive pad. Experimental results indicate that the micro hardness of surface layer becomes lower and the softened layer is formed owing to chemical effect of triethanolamine solution on spinel wafers. The softened layer formation in triethanolamine solution and de-ionized water is attributed to the chemical reactions of CO2 and OH-, and the softened layer thickness in triethanolamine solution is 2 nm, but that in de-ionized water is less than 0.65 nm. However, the material removal rate in the lapping with triethanolamine solution is higher than that with de-ionized water, but the surface quality in the condition as mentioned above is worse than that with de-ionized water. It concludes that the chemical influence of triethanolamine solution could greatly enhance the material removal rates.Keywords：triethanolamine;spinel;fixed abrasive;lapping;Softened Layer- 59
- |
- 8
- |
- 6
Published：2020-08-13 -
Anti-impact material properties of UV-LIGA multi-layered electroformed nickel
Abstract：To explore the mechanical reliability of multi-layered electroformed nickel prepared by UV-LIGA (Ultraviolet Lithography, Galvanoformung, Abformung) multi-layered manufacturing technology, the anti-impact material properties of the multi-layered electroformed nickel were analyzed. High-speed impact tests for the multi-layered electroformed nickel were completed by adopting an impact testing device and a signal acquisition system. The experimental results show that the cumulative failure probability - peak acceleration curve approximately fits the Weibull statistical distribution, the Weibull coefficient is 7.6 and the reference acceleration is 21 300g. When the acceleration is 12 000-18 000g, it shows a higher reliability; when that is 12000-18 000g, the cumulative failure probability increases greatly; however the reliability is declines rapidly at acceleration more than 24000g. A Scanning Electron Microscopy(SEM) was used to observe the samples and the results show that the delamination, fracture, plastic deformation and adhesion are the main failure modes. Finally, the failure causes were analyzed and corresponding optimization methods were proposed to improve the process of UV-LIGA multi-layered electroformed nickel, which verifies that the experiments provide bases for design of a multi layer structure of UV-LIGA.Keywords：Ultraviolet Lithography Galvanoformung Abformung(UV-LIGA);multi-layered electroformed nickel;anti-impact property;Micro-mechanic-electronic System(MEMS)- 69
- |
- 8
- |
- 3
Published：2020-08-13 -
Thermal control system of carbon dioxide detection instrument
Abstract：According to the structure characteristics and working modes of a dioxide detection instrument and considering its space environments, a thermal control system for the detection instrument was designed by combination of passive thermal control and active thermal control. Firstly, the structure and the internal heat source were introduced, the heat flux of the instrument was analyzed, and the difficulties of thermal control were obtained. Then, the thermal design of the instrument was carried out and the combination method of passive thermal control and active thermal control was used for the thermal isolation, thermal transmission and the thermal compensation. According to the space environment and thermal control measures, a thermal analysis model was constructed and the thermal transfer was solved with a TMG code. The simulation results show that the temperature of the main frame in the optical system is 13.3 ℃-21.7 ℃, which meets the design requirements. Finally, the thermal design was verified with a vacuum thermal balance test and the test results indicate that the temperature of the main frame in the optical system is 13.0 ℃-20.3 ℃. The tested value is in agreement with the calculated ones, which meets the thermal design targets and verifies that the thermal design is reasonable.Keywords：carbon dioxide detection instrument;thermal control system;thermal design;thermal analysis;thermal test- 57
- |
- 11
- |
- 4
Published：2020-08-13 -
High efficiency multi-jet electrospraying of nano particles with assisted gas
Abstract：A novel multi-jet electrospray with assisted gas was explored to eject nano particles in a high efficiency. The electrospray spinneret with multi nozzles was designed to guide the assisted gas to form the uniform sheath gas around each nozzle and to provide the excess stretching and restriction forces on the charged electrospray jets. The obtained sheath gas decreases the surface charge density of charged electrospray jets and the interferences among charged jets and makes stable multi electrospray jets for continuously ejection for a long time. The ejection and deposition behaviors of multi electrospray jets were investigated and the effects of sheath gas on the threshold voltage of multi electrospray jet ejection and the uniformity of nano particles were analyzed. The experiments show that the sheath gas is beneficial to the decrease of threshold voltages of multi electrospray jets and the diameters of electrospray nano particles and to the increase of the uniformity of nano particles. When the supply pressure of assisted gas increases from 0 kPa to 50 kPa, the threshold voltage of multi electrospray jet ejection decreases from 4.9 kV to 2.8 kV and the average diameter of nano particles decreases from 845.267 nm to 528.06 nm. It concludes that introducing the assisted gas into electrospray spinneret provides a good way to rapidly fabricate the nano particles through multi-jet electrospray. This work would promote the application research of electrospray technology.Keywords：electrospraying;nano particle;multi-jet ejection;sheath gas;focused restriction- 61
- |
- 9
- |
- 3
Published：2020-08-13 -
Complete stiffness model and stiffness performance of 5-U P S/ P RPU redundantly actuated parallel machine tool
Abstract：A complete stiffness model of the 5-UPS/PRPU redundantly actuated parallel machine tool was constructed based on the overall Jacobian matrix and the principle of virtual working. Firstly, the Jacobian matrix of a constraint limb was derived by using screw theory; then, the Jacobian matrix of actuations was derived by using the theory of reciprocal screw and by locking actuated joint in each limb; finally, a redundant Jacobian matrix was designed. By using the mapping relationship between constraint forces, actuated forces, redundantly actuated forces and external forces, the complete stiffness model of the overall system was obtained combining with the principle of virtual work. Furthermore, by taking the effect of the axial deformation of a universal joint, a spherical joint and some other transmission parts on the linear stiffness of each limb into consideration, the axial line stiffness model of each single limb was constructed. The stiffness model was further validated by a laser tracker. The experiment results show that the error of stiffness model is 2%-5%, which means that the theoretical analysis is acceptable. On this basis, the stiffness performance of the machine tool was evaluated by utilizing the minimum linear/angle stiffness values, the minimum stiffness distribution in the workspace was investigated, and the minimum stiffness area was generalized. It shows that the minimum linear stiffness distributes on both sides of Y-axis, the minimum angle stiffness distributes on the -0.05≤z≤0.05 m and -0.11≤y≤-0.05 m, which suggests that the programmer should avoid this area when the trajectory of the Parallel Machine Tool(PMT) is planned. The research provides a theoretical reference for the track programming of the 5-UPS/PRPU redundantly actuated PMT.Keywords：parallel machine tool;actuation redundancy;complete stiffness model;minimum stiffness distribution- 56
- |
- 11
- |
- 6
Published：2020-08-13 -
Feedforward compensation control of X-Y precise positioning table using inversed-sensitive function
Abstract：As the stable state error of an X-Y precise positioning table driven by a Voice Coil Motor(VCM) will lead to a poor position precision, a feedforward compensation method based on inversed-sensitive function was proposed. Firstly, the system model was set up based on frequency domain identification, and the relationship between system disturbances and steady state error was established using final-value theorem. Then, an inversed-sensitive function was designed to compensate the effect of the disturbances on the stable error and to improve the positioning accuracy of the system. Finally, the experiments of different strokes were implemented on the X-Y table driven directly by the VCM to validate the efficacy of the proposed method. The experimental results show that the static errors of the system decrease from 2 μm to 0.2 μm with a micro positioning of 10 μm and a maximum acceleration of 6 mm/s2, and those decrease from 2 μm to 0.4 μm with a macro positioning of 10 mm and a maximum acceleration of 6 m/s2. Obtained achievements verify the validity of the proposed method and provide a references for the subsequent study in high accuracy positioning servo system design.Keywords：voice coil motor;precise positioning table;sensitivity function;feedforword compensation- 60
- |
- 9
- |
- 3
Published：2020-08-13 -
Hex-Rotor unmanned aerial vehicle controller and its flight experiment under aerodynamic disturbance
Abstract：The downside effects of airflow disturbance and rotor interference on the control accuracy and control effect of a unmanned aerial vehicle were analyzed and the method to solve the problems mentioned above was given. A dynamic model for the Hex-Rotor aircraft was established, and the reasons that control quality of aircraft was declined by the fluctuation of lift factors were analyzed. An inversion sliding mode controller was designed to control the space 6-DOF channels, meanwhile a nonlinear supercoiled observer was proposed based on the nondetermination of lift factors to estimate the lift factor of every rotor and to overcome the pneumatic disturbance. A prototype was taken to verify the proposed method. The experiment results indicate that the horizontal tracking errors are limited in ±4.5 m with the altitude error of ±2.5 m and attitude errors of ±2° in a large inflow environment. The method effectively estimates the lift factor of every rotor and improves the control precision and effect of the Hex-Rotor aircraft.Keywords：unmanned aerial vehicle;lift factor;aerodynamic disturbance;inversion sliding mode controller;supercoiled nonlinear observer- 56
- |
- 6
- |
- 4
Published：2020-08-13 -
Multi-objective optimization of micro-manipulation stage based on response surface method
Abstract：To improve the operating space and dynamic characteristics of micro-manipulation stages, the multi-objective optimization design was performed for a new micro-manipulation stage based on response surface method. The central composite design method was used to select test points and the parametric geometric modeling of the stage was built based on the test points. The software ANSYS was uesd to carry out statics and modal analysis to obtain the response values of natural frequency, displacement amplification ratio and the maximum stress of the stage. Then, the least square method and the test of significance were employed to build the two-order polynomial response surface model to reflect the performance index of the stage according to the simulation test data. The evaluation indexes reflecting fitting degree of the response surface were calculated to illustrate the veracity of the proposed response surface model. Furthermore, a multi-objective optimization model of micro-manipulation stage was established by taking the displacement magnification and the natural frequency as object functions, the strength as the constraint. The multi-objective genetic algorithm was taken to obtain Pareto solution set. The Pareto solution show that the natural frequency is in conflict with amplification ratio of the stage, so the optimal solution is chosen from Pareto set by weighing the natural frequency and amplification ratio. The comparative analysis of the performance indexes of the stage before and after optimizations shows that the natural frequency and the magnification ratio increase by 35.58 % and 2.33 %, respectively, and the maximum stress decreases by 38.97 %. It illustrate that the proposed optimization method is effective.Keywords：micro-manipulation stage;central composite design;response surface method;multi-objective genetic algorithm- 57
- |
- 12
- |
- 20
Published：2020-08-13 -
Digital integration of PMSM speed controller based on FPGA
Abstract：On the basis of the Field Programming Gate Array(FPGA), a speed controller with anti-windup strategy is designed for the servo control system of a high-performance Permanent Magnet Synchronous Motor(PMSM). Then, a corresponding integrating design method is given. The controller scheme realizes a fully digital and integrated PMSM servo control system on one-chip FPGA. The Nios II embedded processor is used to develop the speed controller strategy and a designed parallel hardware circuit is utilized to implement the current vector controller to meet the requirement of high sampling frequency. To overcome the windup phenomenon owing to integrator saturation under the large set-point changes, a PI speed controller with anti-windup strategy is designed to reduce the overshoot and settling time of the servo control system. Experiment results demonstrate that the proposed controller increases the steady speed accuracy to 10 r/min as compared with the traditional PI controller, and it satisfies the designed requirements of PMSM servo control system with better dynamic and static performance.Keywords：Permanent Magnet Synchronous Motor(PMSM);Field Programming Gate Array(FPGA);anti-windup strategy;speed controller;PI controller- 70
- |
- 14
- |
- 12
Published：2020-08-13 -
Compensation for dynamic measurement errors of time grating sensor
Abstract：According to the error characteristics in dynamic measurement, a targeted respective modeling and a combined compensation idea for systematic errors and random errors were proposed to improve the dynamic measuring accuracy of a time grating sensor. The Fourier series approach was presented to establish the model for the systematic errors with periodical changes, in which the compensation parameters for the systemic errors were calculated by using least square to solve overdetermined equation. Moreover, the grey model GM(1, 1) was used for modeling random errors after compensation systemic errors and the forecast accuracy was improved by a residual error test and modification. The actual experiments show that systematic errors have been effectively compensated by Fourier series approach model, the original errors are reduced from ±35" to ±7.8", and the compensation parameters are consistent with that of actual sensor. The random errors have been forecasted and compensated by GM(1, 1) model, and the random errors are reduced from ±7.8" to ±3". These results demonstrate that proposed method compensates the dynamic errors greatly and the dynamic measurement accuracy of the embedded time grating sensor is effectively improved by using this modeling and compensation method.Keywords：time grating sensor;displacement measurement;dynamic measurement error;systematic error;random error;Fourier series approach;GM(1;1) model- 56
- |
- 10
- |
- 3
Published：2020-08-13 -
Real-time processing of image restoration for space camera
Abstract：To enhance the imaging performance for a space camera, a real-time image restoration method was proposed based on the efficient extraction of Point Spread Function (PSF). The key issues of real-time image restoration were analyzed based on typical image restoration methods. A deconvolution operator was given by combining the PSF with the typical image restoration methods. Then, the real-time recovery processing was carried out in a spatial domain by using a Field Programming Gate Array(FPGA) as the core device. The verified experiments on the remote sensing image data from the space camera were performed on a hardware platform and the restoration results by proposed method were compared with those by typical image restoration methods. The comparative results show that the gray mean gradient of the image from one space camera with 12 000 pixel CCD chip has improved from 3.7887 to 8.2296 and the Laplacian from 15.4567 to 43.9075, which achieves the same performance as that of the typical image restoration methods. The image processing delay is 1.9 ms when the deconvolution operator size is 19 pixel×19 pixel, and the Modulation Transfer Function(MTF) is increased from 0.1 to 0.23 at the Nyqyist frequency. These data demonstrate that the imaging performance within the whole space camera system is significantly improved by the real-time image restoration system.Keywords：space camera;real-time image restoration;deconvolution operator;Field Programmable Gate Array(FPGA)- 67
- |
- 13
- |
- 4
Published：2020-08-13 -
Distributed compressive sensing imaging and reconstruction of hyperspectral imagery
Abstract：According to the characteristics of high spectral data, a distributed compressed sampling model based on pixels was proposed to realize the efficient compressive sampling and reconstruction. A spectral imaging system based on distributed compressed sampling was established and a reconstruction algorithm for this system was investigated. In the image acquisition stage, the hyperspectral data were divided into key pixels and compressive sensing pixels. The ground pixels were separated along the spectral direction by a prism. Then, the linear encoding between the spectral bands was realized by a digital micro-mirror device. The compressive sensing pixels were coded with a low sampling rate, and the key pixels were coded by a sampling rate of 1. In the reconstruction of the compressive sampled data, the traditional compressive sensing reconstruction methods which recover hyperspectral data directly were abandoned. However, the linear mixed models were used to convert the hyperspectral data reconstruction into an endmember extraction and an abundance estimation, then, the hyperspectral data were recovered by using the extracted endmember and estimated abundance. The comparison experiments show that the reconstruction average signal noise rate by proposed algorithm is improved about 10 dB when the used data are 20% that of total data. The system is suitable for the spaceborne or airborne hyperspectral compressive sensing imaging for its less data collected and simple sampling method.Keywords：distributed compressive sensing;hyperspectral imagery;imaging spectrometer;linear mixing model;sensing matrix- 55
- |
- 12
- |
- 12
Published：2020-08-13 -
3D facial similarity comparison in shape space
Abstract：This paper focuses on the 3D facial similarity comparison by using a computer automatically. A new 3D facial similarity comparison method based on a geodesics in a shape space was proposed. In this method, 3D facial surface was approximately represented by a set of geodesics and the corresponding geodesics between two facial models were compared by a elastic metric in the shape space, in which the similarity between two faces could be measured by the average geodesic distance of all corresponding geodesics. 3D facial similarity experiments were perfomed on 28 facial models of 14 persons in Gavadb database and the recognition rate is above 92.86%, which indicates that this method recognizes the facial models of the same person from different person's facial models. In addition, 3D facial similarity experiments on different person's facial models were implemented. The experimental results show that the similarity values computed by proposed method consist with that of people's subjective judgment. These results reflect that the proposed method can measure the similarity of 3D faces well.Keywords：computer graphics;computer vision;3D facial similarity;geodesic;shape space;Square-root Velocity Function (SRVF)- 55
- |
- 10
- |
- 7
Published：2020-08-13 -
Analysis and processing of Morié fringe signals based on non-uniform sampling
Abstract：To measure the dynamic real-time interpolation error of an optical encoder in non-uniform rotation, a method for analysis and processing the Morié fringe signals based on non-uniform sampling was presented. The real Morié fringe signal equation was constructed by Fourier series principle. According to real-time sampling on the encoder at different speeds, the characteristics of non-uniform sampling for Moiré signals was revealed. On the basis of the non-uniformity of the signal sampling, the Morié fringe signals were reconstructed by using the least square curve fitting.Reconstructed signals were analysed by Discrete Fourier Transform algorithm and the waveform parameters were obtained. With the relationship between interpolation error and signal parameters, the measurement of encoder dynamic error was achieved. The Moiré fringe signal of a 21 bit absolute optical encoder was analysed and processed and the twice extreme dynamic interpolation errors are +3.21 ";-4.69" and +3.45 ";-4.81", respectively.Experiment result shows that this method effectively processes Morié fringe signal of variable frequency in the encoder with non-uniform rotation, and accurately measures the dynamic interpolation error of the encoder, which provides foundation for real-time detection and correction of encoder error at the actual work site.Keywords：optical encoder;interpolation error;Moire fringe;non-uniform sample;Discrete Fourier Tranform(DFT)- 57
- |
- 9
- |
- 10
Published：2020-08-13 -
Large capacity FLASH video storage controller base on blanking period of line and field signals
Abstract：A FLASH video storage controller using the blanking period of line and field signals to control time sequence was designed to overcome the disadvantages of complex timing design and large cache resource requirements of traditional ones. The controller was designed based on the Field Programming Gate Array(FPGA) and its reading and writing control commands were input FLASH by line and field signals on the blanking period. In this way, the multistage pipeline could be implemented without cache resources, design control timing was greatly simplified and cache resources were saved. Additionally, a three-stage pipeline was designed based on the Verilog software describing language, which realizes the real-time storage and playback of 2048 pixel×1752 pixel/15 frames in high speed video data with the throughput rate as high as 120 MB/s. Simulation and experiment results show that the system timing design is correct, and large capacity FLASH array reading and writing operation is right. The design can accomplish multifunction operations such as real-time control, storage and the playback of high speed video data.Keywords：FLASH storage controller;large capacity FLASH;Field Programming Gate Array(FPGA);blanking period- 50
- |
- 10
- |
- 4
Published：2020-08-13 -
Target tracking based on incremental deep learning
Abstract：As current tracking algorithms lead to target drift or target loss in the complex environment, a tracking algorithm based on the incremental deep learning was proposed under a double-resampling particle filter framework. To solve the problem of particle degradation and depletion, the double-resampling method was introduced to adapt to the particle size in particle filtering and a Stacked Denoising Autoencoder(SDAE) was pre-trained by the unsupervised feature learning to alleviate the lack of training samples in visual tracking. Then, the SDAE was applied to online tracking, so that the extracted feature sets could express the region image representations of the particles effectively. The incremental feature learning was introduced to the encoder of SDAE, the feature sets were optimized by adding new features and merging the similar features to adapt to appearance changes of the moving object. Moreover, a support vector machine was used to classify the features then to improve the classification accuracy of the particles and to obtain a higher tracking precision. According to the results of experiments on variant challenging image sequences in the complex environment, the F-measure and the overlapping ratio of the presented algorithm are 94%, 74%, respectively and the average frame rate is 13 frame/s. Compared with the state-of-the-art tracking algorithms, the proposed method solves the problems of target drift and target loss efficiently and has better robust and higher accuracy, especially for the target in the occlusions, background clutter, illumination changes and appearance changes.Keywords：target tracking;partical filter;stacked denoising autoencoder;support vector machine;incremental feature;deep learning- 45
- |
- 9
- |
- 16
Published：2020-08-13 -
Image completion with global optimization based on four-direction features
Abstract：To better maintain the structure coherence and neighborhood consistence of inpainted images, this paper proposes an image completion algorithm by using global optimization based on four-direction features. In the algorithm, the Curvelet transform was adopted to extract the features in horizontal, vertical, positive diagonal and antidiagonal directions. when the data term and smooth term energy were constructed, the four-direction features were combined with color information to measure the similarity between patches and to construct a global energy constraint equation to satisfy human eye visual requirement. Meanwhile, the sizes of patches used to compute data term and smooth term energy were adaptively determined. Finally, the graph cut algorithm was applied to calculation of the minimum value of global energy to obtain the inpainted image. The experimental results show that the proposed algorithm achieves better inpainted results. Moreover, the Peak Signal to Noise Ratio(PSNR) values of the proposed method are much larger than that of the existing methods, and the PSNR on average is higher 2 dB than that of the existing methods. The objective and subjective evaluations both show the validity of the proposed method. It concludes that the proposed algorithm has better maintained the structure coherence and neighborhood consistence, which makes the repaired images meet the human eye visual requirements.Keywords：image completion;object removal;global optimization;four-direction feature- 43
- |
- 8
- |
- 2
Published：2020-08-13 -
No-reference laser-dazzling image quality assessment based on feature-point complexity
Abstract：The validity of target recognition and target detection depend on the accuracy of target extraction, this paper establishes an experiment platform of laser active imaging system combining laser active image technology and target recognition technology. The image quality and feature-point extraction were researched in the target area after laser jamming, and a new No-reference Feature-point Complexity Metrics(NRFPCM) assessment algorithm was proposed. In the algorithm, the feature-point, texture, gradient and contrast complexity were computed in the target area, then the normalized NRFPCM was obtained via production of the four factors above. Finally, the luminance imaging experiment was performed for the target by utilizing the laser active imaging system and the disturbed images with different disturbing powers and different spot positions were obtained. The proposed NRFPCM algorithm was used to evaluate the standard image database and the newly obtained laser-dazzling images. The results show that the proposed algorithm reflects the image quality objectively and gives a more reasonable evaluation results for different laser-dazzling images. Moreover, evaluation results are more suitable for the subjective visual feeling. The NRFPCM gives the guidance to the laser active imaging system in the defense and application.Keywords：image processing;image quality assessment;laser-dazzling;feature-point similarity;target recognition- 61
- |
- 9
- |
- 6
Published：2020-08-13 -
Automatic localization and segmentation of optic disk in color fundus image
Abstract：An effective pre-processing method is proposed to overcome the influence of a bright ring caused by the edge of a color fundus image on optic disk localization. Then, a novel method integrating the morphology, ellipse fitting and a Gradient Vector Flow (GVF) Snake model is proposed to implement the segmentation of the optic disk. The proposed pre-processing method uses least square method to fit the edge of color fundus image, and then clips some bright pixels near the edge. Finally, it localizes the optic disk. Furthermore, the proposed segmentation algorithm segments the optic disk by 3 steps: vascular erase, ellipse fitting and a fine tune step using GVF Snake model. A test is performed with 1 200 color fundus images from Messidor color fundus image database. The test results indicate that the localization accuracy for the optic disk rises from 95.4% to 98.7% as comparing with the traditional method. Moreover, the optic disk segmentation error has dropped from 12.5% to 9.39% as comparing with the current known best algorithm. It concludes that the proposed method of automatic localization and segmentation of optic disk in color fundus images have strong practicability and high accuracy and are suitable for the computer-aided diagnosis of ocular diseases.Keywords：color fundus image;image preprocessing;optic disk localization;optic disk segmentation- 63
- |
- 11
- |
- 12
Published：2020-08-13 -
Point wise distortion correction algorithm with vanishing point collinear constraint
Abstract：Point wise correction algorithms are researched and analyzed. The correction accuracy of a point wise distortion correction algorithm based on four-point collinear cross ratio invariability is investigated. It points out that the initial used image points which contain errors will cause the accuracy change in the calculation of other image points. Then, it gives the selection method for image point locations and relative distances when the calculation error is smaller. Based on the above, this paper proposes a point wise distortion correction algorithm based on vanishing point collinear constraint. The algorithm uses vanishing points to improve the linear fit accuracy and the collinear feature to constrain the corrected distortion accuracy. It not only optimizes the image point errors of the distortion correction algorithm based on a four-point collinear cross ratio invariance, but also the initial image point errors, so that the accuracy of distortion correction of all image points is improved ultimately. The simulation based on MATLAB shows that the maximum error of corrected image points is 29.05 times that of the initial image point noise for four million pixels. In contrast to the physical image using the cross ratios from the correction algorithms based on four-point collinear invariant cross ratio and vanishing point collinear constraint as well the uncorrected image, it indicates that the performance of proposed algorithm is better than that of the algorithm based on four-point collinear cross ratio invariance.Keywords：computer vision;image correction;distortion correction;vanishing point;cross-ratio invariability;collinear constraint- 69
- |
- 11
- |
- 3
Published：2020-08-13
Loading...
0