Zheng You

Tsinghua University, Peping, Beijing, China

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Publications (80)82.77 Total impact

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    ABSTRACT: Polarization navigation is a promising orientation-determination method inspired by insects’ foraging behavior that offers the advantages of autonomous and high precision. In this paper, using the solar meridian as an azimuth reference is proposed. The model of the distribution pattern of the polarized skylight projected onto an imaging sensor is analyzed. The sufficient features of the solar meridian are proven. According to these features, an angle algorithm for an imaging polarization navigation sensor based on a machine-vision algorithm is proposed. In consideration of noise in images, the relation between the measured angle and the noise in images is modeled. This model cannot only optimize the threshold tolerance R in the algorithm but also describe the effects of several primary factors that can affect the measuring precision. In the simulation test, the measurement accuracy was better than 0.34°. When the algorithm was tested on the polarization-detection system, the measurement accuracy was better than 0.37°.
    Optics Express 03/2015; 23(6). DOI:10.1364/OE.23.007248 · 3.53 Impact Factor
  • Jin Li, Fei Xing, Ting Sun, Zheng You
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    ABSTRACT: Modulation transfer function (MTF) can be used to evaluate the imaging performance of on-board optical remote sensing sensors, as well as recover and restore images to improve imaging quality. Laboratory measurement approaches for MTF have achieved high precision. However, they are not yet suitable for on-board measurement. In this paper, a new five-step approach to calculate MTF of space optical remote sensing sensors is proposed. First, a pixel motion model is used to extract the conditional sub-frame images. Second, a mathematical morphology algorithm and a correlation–homomorphic filter algorithm are used to eliminate noise and enhance sub-frame image. Third, an image partial differentiation determines the accurate position of edge points. Fourth, a model optical function is used to build a high-resolution edge spread function. Finally, MTF is calculated by derivation and Fourier transform. The experiment shows that the assessment method of MTF is superior to others.
    Optics Express 03/2015; 23(5). DOI:10.1364/OE.23.006187 · 3.53 Impact Factor
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    ABSTRACT: MEMS relays/switches have been some of the most interesting hotspots in all kinds of MEMS devices for decades. Electrostatic actuation is the most popular actuation principle. A novel in-plane electrostatic comb-drive actuator for MEMS relays/switches was designed and fabricated. Double-tilt comb fingers and tilted parallelogram beams were proposed to achieve the requirements of MEMS relays/switches. The restoring force curve, actuation force curve, and pull-in voltage were measured. Double-tilt fingers were found to have a larger actuation force than traditional rectangular fingers, and the pull-in voltage was decreased by 25% by replacing rectangular fingers with double-tilt fingers. In addition, tilted parallelogram beams provided a convex upward restoring force curve, which was more suitable for MEMS relays/switches than the conventional force curve.
    Journal of Micromechanics and Microengineering 01/2015; 25(4). DOI:10.1088/0960-1317/25/4/045003 · 1.73 Impact Factor
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    ABSTRACT: Super-black materials based on Nanotechnology have very important applications in many science fields. Super-black materials which have been reported currently, although have excellent light-trapping properties, most of them need the use of sophisticated equipment , the long-time synthesis , high temperature environment and release flammable, explosive and other dangerous gases. So many kinds of problems have hindered the application of such super-black material in practice. This project had nano super-black material developed with simple equipment and process, instead of complicated and dangerous process steps in high temperature and high pressure. On the basis of literature research, we successfully worked out a set of large-area Ni-P alloy plating method through a series of experiments exploring and analyze the experimental results. In the condition of the above Ni-P alloy, we took the solution, which anodized the Ni-P alloy immersed in the non-oxidizing acid, instead of conventional blackening process. It`s a big break for changing the situation in which oxidation, corrosion, vigorous evolution of hydrogen gas in the process are performed at the same location. As a result, not only the reaction process decreased sensitivity to time error, but also the position of the bubble layer no longer located in the surface of the workpiece which may impede observing the process of reaction. Consequently, the solution improved the controllability of the blackening process. In addition, we conducted the research of nano super-black material, exploring nano-super-black material in terms of space optical sensor.
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    ABSTRACT: To improve the accuracy of digital sun sensors (DSS) to the level of arc-second while maintaining a large field of view (FOV), a multiplexing image detector method was proposed. Based on a single multiplexing detector, a dedicated mask with different groups of encoding apertures was utilized to divide the whole FOV into several sub-FOVs, every of which would cover the whole detector. In this paper, we present a novel method to analyze and optimize the diffraction effect and the parameters of the aperture patterns in the dedicated mask, including the aperture size, focal length, FOV, as well as the clearance between adjacent apertures. Based on the simulation, a dedicated mask with 13 × 13 various groups of apertures was designed and fabricated; furthermore a prototype of DSS with a single multiplexing detector and 13 × 13 sub-FOVs was built and test. The results indicated that the DSS prototype could reach the accuracy of 5 arc-second (3σ) within a 105° × 105° FOV. Using this method, the sun sensor still keeps the original features of low power consumption, small size and high dynamic range when it realizes both high accuracy and large FOV.
    Optics Express 09/2014; 22(19). DOI:10.1364/OE.22.023094 · 3.53 Impact Factor
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    Jin Li, Fei Xing, Zheng You
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    ABSTRACT: Recently, the discrete wavelet transforms- (DWT-) based compressor, such as JPEG2000 and CCSDS-IDC, is widely seen as the state of the art compression scheme for charge coupled devices (CCD) camera. However, CCD images project on the DWT basis to produce a large number of large amplitude high-frequency coefficients because these images have a large number of complex texture and contour information, which are disadvantage for the later coding. In this paper, we proposed a low-complexity posttransform coupled with compressing sensing (PT-CS) compression approach for remote sensing image. First, the DWT is applied to the remote sensing image. Then, a pair base posttransform is applied to the DWT coefficients. The pair base are DCT base and Hadamard base, which can be used on the high and low bit-rate, respectively. The best posttransform is selected by the l p -norm-based approach. The posttransform is considered as the sparse representation stage of CS. The posttransform coefficients are resampled by sensing measurement matrix. Experimental results on on-board CCD camera images show that the proposed approach significantly outperforms the CCSDS-IDC-based coder, and its performance is comparable to that of the JPEG2000 at low bit rate and it does not have the high excessive implementation complexity of JPEG2000.
    07/2014; 2014:840762. DOI:10.1155/2014/840762
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    Jin Li, Fei Xing, Ting Sun, Zheng You
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    ABSTRACT: Remote sensing multispectral image compression encoder requires low complexity, high robust, and high performance because it usually works on the satellite where the resources, such as power, memory, and processing capacity, are limited. For multispectral images, the compression algorithms based on 3D transform (like 3D DWT, 3D DCT) are too complex to be implemented in space mission. In this paper, we proposed a compression algorithm based on distributed source coding (DSC) combined with image data compression (IDC) approach recommended by CCSDS for multispectral images, which has low complexity, high robust, and high performance. First, each band is sparsely represented by DWT to obtain wavelet coefficients. Then, the wavelet coefficients are encoded by bit plane encoder (BPE). Finally, the BPE is merged to the DSC strategy of Slepian-Wolf (SW) based on QC-LDPC by deep coupling way to remove the residual redundancy between the adjacent bands. A series of multispectral images is used to test our algorithm. Experimental results show that the proposed DSC combined with the CCSDS-IDC (DSC-CCSDS)-based algorithm has better compression performance than the traditional compression approaches.
    07/2014; 2014:738735. DOI:10.1155/2014/738735
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    ABSTRACT: Star trackers and gyroscopes are the two most widely used attitude measurement devices in spacecrafts. The star tracker is supposed to have the highest accuracy in stable conditions among different types of attitude measurement devices. In general, to detect faint stars and reduce the size of the star tracker, a method with long exposure time method is usually used. Thus, under dynamic conditions, smearing of the star image may appear and result in decreased accuracy or even failed extraction of the star spot. This may cause inaccuracies in attitude measurement. Gyros have relatively good dynamic performance and are usually used in combination with star trackers. However, current combination methods focus mainly on the data fusion of the output attitude data levels, which are inadequate for utilizing and processing internal blurred star image information. A method for tracking deep coupling stars and MEMS-gyro data is proposed in this work. The method achieves deep fusion at the star image level. First, dynamic star image processing is performed based on the angular velocity information of the MEMS-gyro. Signal-to-noise ratio (SNR) of the star spot could be improved, and extraction is achieved more effectively. Then, a prediction model for optimal estimation of the star spot position is obtained through the MEMS-gyro, and an extended Kalman filter is introduced. Meanwhile, the MEMS-gyro drift can be estimated and compensated though the proposed method. These enable the star tracker to achieve high star centroid determination accuracy under dynamic conditions. The MEMS-gyro drift can be corrected even when attitude data of the star tracker are unable to be solved and only one navigation star is captured in the field of view. Laboratory experiments were performed to verify the effectiveness of the proposed method and the whole system.
    Measurement Science and Technology 07/2014; 25(8):085003. DOI:10.1088/0957-0233/25/8/085003 · 1.35 Impact Factor
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    Hao Li, Gaofei Zhang, Rui Ma, Zheng You
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    ABSTRACT: An effective multisource energy harvesting system is presented as power supply for wireless sensor nodes (WSNs). The advanced system contains not only an expandable power management module including control of the charging and discharging process of the lithium polymer battery but also an energy harvesting system using the maximum power point tracking (MPPT) circuit with analog driving scheme for the collection of both solar and vibration energy sources. Since the MPPT and the power management module are utilized, the system is able to effectively achieve a low power consumption. Furthermore, a super capacitor is integrated in the system so that current fluctuations of the lithium polymer battery during the charging and discharging processes can be properly reduced. In addition, through a simple analog switch circuit with low power consumption, the proposed system can successfully switch the power supply path according to the ambient energy sources and load power automatically. A practical WSNs platform shows that efficiency of the energy harvesting system can reach about 75-85% through the 24-hour environmental test, which confirms that the proposed system can be used as a long-term continuous power supply for WSNs.
    06/2014; 2014:671280. DOI:10.1155/2014/671280
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    ABSTRACT: The star tracker is one of the most promising attitude measurement devices widely used in spacecraft for its high accuracy. High dynamic performance is becoming its major restriction, and requires immediate focus and promotion. A star image restoration approach based on the motion degradation model of variable angular velocity is proposed in this paper. This method can overcome the problem of energy dispersion and signal to noise ratio (SNR) decrease resulting from the smearing of the star spot, thus preventing failed extraction and decreased star centroid accuracy. Simulations and laboratory experiments are conducted to verify the proposed methods. The restoration results demonstrate that the described method can recover the star spot from a long motion trail to the shape of Gaussian distribution under the conditions of variable angular velocity and long exposure time. The energy of the star spot can be concentrated to ensure high SNR and high position accuracy. These features are crucial to the subsequent star extraction and the whole performance of the star tracker.
    Optics Express 03/2014; 22(5):6009-24. DOI:10.1364/OE.22.006009 · 3.53 Impact Factor
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    ABSTRACT: This paper investigates the type synthesis of 2T1R-type (T: translational degree of freedom (DoF) and R: rotational DoF) parallel kinematic mechanisms (PKMs). A type synthesis method based on Grassmann Line Geometry and Line-graph Method is introduced. Some basic criterions of Grassmann Line Geometry are briefly summarized, and the Line-graph Method is presented sequentially. In order to uncover the relationship between DoF-line graph and constraint-line graph, the dual rule is brought in and explained in detail. Based on these foundations, the technological process of the type synthesis is given. Thereafter, the type synthesis of 2T1R-type PKMs is carried out and the results are listed. Taken as an application example, a synthesized 3-DoF mechanism is chosen as the parallel module of a five-axis hybrid machine tool, which is capable of five-face machining in one setup. The developed prototype is introduced and applied into the machining of a part with freeform surfaces. The presented type synthesis method is concise and can be used in the type synthesis of other PKMs.
    Robotics and Computer-Integrated Manufacturing 02/2014; 30(1):1–10. DOI:10.1016/j.rcim.2013.07.002 · 1.84 Impact Factor
  • Mathematical Problems in Engineering 01/2014; 2014:1-16. DOI:10.1155/2014/432613 · 1.08 Impact Factor
  • Jin Li, Fei Xing, Ting Sun, Zheng You
    Journal of Applied Mathematics 01/2014; 2014:1-8. DOI:10.1155/2014/374285 · 0.72 Impact Factor
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    Minsong Wei, Fei Xing, Zheng You
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    ABSTRACT: Stringent attitude determination accuracy through a high bandwidth is required for the development of the advanced space technologies, such as earth observation and laser communication. In this work, we presented a novel proposal for a digital sun sensor with high accuracy, large Field of View (FOV) and ultra-high data update rate. The Electronic Rolling Shutter (ERS) imaging mode of an APS CMOS detector was employed and an "amplifier factor" was introduced to improve the data update rate significantly. Based on the idea of the multiplexing detector, a novel mask integrated with two kinds of aperture patterns was also introduced to implement its distinctive performance of high precision and large FOV. Test results show that the ERS based sun sensor is capable of achieving the data update rate of 1 kHz and precision of 1.1″ (1σ) within a 105° × 105° FOV. The digital sun sensor can play an important role in precise attitude determination and provide a broader application for high accuracy satellites.
    Optics Express 12/2013; 21(26):32524-33. DOI:10.1364/OE.21.032524 · 3.53 Impact Factor
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    ABSTRACT: In order to avoid a potential waste of energy during consensus controls in the case where there exist measurement uncertainties, a nonlinear protocol is proposed for multiagent systems under a fixed connected undirected communication topology and extended to both the cases with full and partial access a reference. Distributed estimators are utilized to help all agents agree on the understandings of the reference, even though there may be some agents which cannot access to the reference directly. An additional condition is also considered, where self-known configuration offsets are desired. Theoretical analyses of stability are given. Finally, simulations are performed, and results show that the proposed protocols can lead agents to achieve loose consensus and work effectively with less energy cost to keep the formation, which have illustrated the theoretical results.
    Mathematical Problems in Engineering 09/2013; 2013. DOI:10.1155/2013/794346 · 1.08 Impact Factor
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    ABSTRACT: The star tracker is one of the most promising attitude measurement devices used in spacecraft due to its extremely high accuracy. However, high dynamic performance is still one of its constraints. Smearing appears, making it more difficult to distinguish the energy dispersive star point from the noise. An effective star acquisition approach for motion-blurred star image is proposed in this work. The correlation filter and mathematical morphology algorithm is combined to enhance the signal energy and evaluate slowly varying background noise. The star point can be separated from most types of noise in this manner, making extraction and recognition easier. Partial image differentiation is then utilized to obtain the motion parameters from only one image of the star tracker based on the above process. Considering the motion model, the reference window is adopted to perform centroid determination. Star acquisition results of real on-orbit star images and laboratory validation experiments demonstrate that the method described in this work is effective and the dynamic performance of the star tracker could be improved along with more identified stars and guaranteed position accuracy of the star point.
    Optics Express 08/2013; 21(17):20096-20110. DOI:10.1364/OE.21.020096 · 3.53 Impact Factor
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    ABSTRACT: Star tracker is the most accurate attitude sensor for satellite. Generally speaking, the higher the accuracy, the fainter the star can be sensed by the star tracker. How to extract the faint star from a star image is becoming a critical technology in dynamic condition for star tracker, especially using the APS (Active Pixels Sensor) detector. A novel APS star tracker with MEMS Gyroscope aided system was proposed in this paper that could extremely improve the detection effect and capability for the faint stars. During the exposure time of star tracker, the trajectory of star projection on the detector maybe occupy more than ten pixels due to the satellite rotation. In this situation, the signal-to-noise ratio will decline sharply, and the traditional star extraction method for faint star will take no effect. As a result, the accuracy of star tracker would decline sharply, even more, couldn’t work. Using the MEMS Gyroscope, the track of star projection can be predicated and measured, on the basis of which the deconvolution algorithm could be taken to recover the faint star signal. The accuracy of the star projection centroid could be improved obviously, and the dynamic performance of the star tracker would be improved by a magnitude. Meanwhile, the MEMS gyroscope has not less volume, mass and power consumption, which make it more suitable for the application of APS star tracker.
    ISPDI 2013 - Fifth International Symposium on Photoelectronic Detection and Imaging; 08/2013
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    ABSTRACT: Lightweight agile remote sensors have become one type of the most important payloads and were widely utilized in space reconnaissance and resource survey. These imaging sensors are designed to obtain the high spatial, temporary and spectral resolution imageries. Key techniques in instrumentation include flexible maneuvering, advanced imaging control algorithms and integrative measuring techniques, which are closely correlative or even acting as the bottle-necks for each other. Therefore, mutual restrictive problems must be solved and optimized. Optical flow is the critical model which to be fully represented in the information transferring as well as radiation energy flowing in dynamic imaging. For agile sensors, especially with wide-field-of view, imaging optical flows may distort and deviate seriously when they perform large angle attitude maneuvering imaging. The phenomena are mainly attributed to the geometrical characteristics of the three-dimensional earth surface as well as the coupled effects due to the complicated relative motion between the sensor and scene. Under this circumstance, velocity fields distribute nonlinearly, the imageries may badly be smeared or probably the geometrical structures are changed since the image velocity matching errors are not having been eliminated perfectly. In this paper, precise imaging optical flow model is established for agile remote sensors, for which optical flows evolving is factorized by two forms, which respectively due to translational movement and image shape changing. Moreover, base on that, agile remote sensors instrumentation was investigated. The main techniques which concern optical flow modeling include integrative design with lightweight star sensors along with micro inertial measurement units and corresponding data fusion, the assemblies of focal plane layout and control, imageries post processing for agile remote sensors etc. Some experiments show that the optical analyzing method is effective to eliminate the limitations for the performance indexes, and succeeded to be applied for integrative system design. Finally, a principle prototype of agile remote sensor designed by the method is discussed.
    Proceedings of SPIE - The International Society for Optical Engineering 08/2013; DOI:10.1117/12.2034008 · 0.20 Impact Factor
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    ABSTRACT: The earth sensors are currently used in spacecrafts. Most of them with a single field of view (FOV) for earth observation are not applied to aircrafts in the atmosphere. For the use of the aircraft at 70 ~ 100km in the atmosphere, this paper proposes a separate triple-FOV earth sensor based on infrared detectors. By sensing the earth-horizon, the triple-FOV earth sensor obtains the geocentric vector, and calculates the altitude of the aircraft at the same time. The earth sensor uses three pieces of infrared detectors at 14 ~ 16μm. To sense the infrared light could ensure that the earth sensor does the same operation at night and day regardless of the weather and the light impact of the sun and the moon. The optical axes of the three fields of view are positioned at 120° from each other in the horizontal plane, and the angle between the optical axes and the vertical direction is 82.86°. Considering the model of the surface of the earth's atmosphere, the earth's radius and so on, the mathematical model of the triple-FOV earth sensor is established. From 70km to 100km, the result of simulation shows that the altitude measurement accuracy is better than 100m and the angle measurement error is 3.8". The earth sensor can provide high-precision position information, and make data fusion with additional sensors to achieve autonomous navigation of aircrafts.
    Proceedings of SPIE - The International Society for Optical Engineering 08/2013; DOI:10.1117/12.2034608 · 0.20 Impact Factor
  • Nan Chen, Fei Xing, Zheng You
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    ABSTRACT: Along with the development of MEMS technology, the precision of MEMS-Gyro is increasing and the range of application of MEMS-Gyro is expanding. The accuracy of centroid determination of the spot directly relates to the precision of star tracker, but, when the exposure time is shorter or the satellite is in an unstable state, the noise of detector limits the accuracy greatly in the traditional approach of centroid determination. In view of these issues, this paper presents an approach which is based on high-precision MEMS-Gyro to determine the centroid of spot. This approach references EKF to estimate the position of centroid optimally. So, when the SNR is reduced because of shorter exposure and unstable state, this approach can help to increase the accuracy of centroid determination by introducing MEMS-Gyro. Further, it improves the precision and dynamic performance of the star tracker. In the end of this article, the feasibility of the approach is verified by the numerical simulation.
    Key Engineering Materials 07/2013; 562-565:350-356. DOI:10.4028/www.scientific.net/KEM.562-565.350 · 0.19 Impact Factor