Due to unreliable and bandwidth-limited characteristics of communication link in networked control systems,the realtime compensated methods for single-output systems and multioutput systems are proposed in this paper ...Due to unreliable and bandwidth-limited characteristics of communication link in networked control systems,the realtime compensated methods for single-output systems and multioutput systems are proposed in this paper based on the compressed sensing(CS)theory and sliding window technique,by which the estimates of dropping data packets in the feedback channel are obtained and the performance degradation induced by packet drops is reduced.Specifically,in order to reduce the cumulative error caused by the algorithm,the compensated estimates for single-output systems are corrected via the regularization term;considering the process of single-packet transmission,a new sequential CS framework of sensor data streams is introduced to effectively compensate the dropping packet on single-channel of multi-output systems;in presence of the medium access constraints on multi-channel,the communication sequence for scheduling is coupled to the algorithm and the estimates of the multiple sensors for multi-output systems are obtained via the regularization term.Simulation results illustrate that the proposed methods perform well and receive satisfactory performance.展开更多
In recent years,there is a scenario in urban tunnel constructions to build super-large-span tunnels for traffic diversion and route optimization purposes.However,the increased size makes tunnel support more difficult....In recent years,there is a scenario in urban tunnel constructions to build super-large-span tunnels for traffic diversion and route optimization purposes.However,the increased size makes tunnel support more difficult.Unfortunately,there are few studies on the failure and support mechanism of the surrounding rocks in the excavation of supported tunnel,while most model tests of super-large-span tunnels focus on the failure characteristics of surrounding rocks in tunnel excavation without supports.Based on excavation compensation method(ECM),model tests of a super-large-span tunnel excavation by different anchor cable support methods in the initial support stage were carried out.The results indicate that during excavation of super-large-span tunnel,the stress and displacement of the shallow surrounding rocks decrease,following a step-shape pattern,and the tunnel failure is mainly concentrated on the vault and spandrel areas.Compared with conventional anchor cable supports,the NPR(negative Poisson’s ratio)anchor cable support is more suitable for the initial support stage of the super-large-span tunnels.The tunnel support theory,model test materials,methods,and the results obtained in this study could provide references for study of similar super-large-span tunnels。展开更多
Rockburst disasters occur frequently during deep underground excavation,yet traditional concepts and methods can hardly meet the requirements for support under high geo-stress conditions.Consequently,rockburst control...Rockburst disasters occur frequently during deep underground excavation,yet traditional concepts and methods can hardly meet the requirements for support under high geo-stress conditions.Consequently,rockburst control remains challenging in the engineering field.In this study,the mechanism of excavation-induced rockburst was briefly described,and it was proposed to apply the excavation compensation method(ECM)to rockburst control.Moreover,a field test was carried out on the Qinling Water Conveyance Tunnel.The following beneficial findings were obtained:Excavation leads to changes in the engineering stress state of surrounding rock and results in the generation of excess energy DE,which is the fundamental cause of rockburst.The ECM,which aims to offset the deep excavation effect and lower the risk of rockburst,is an active support strategy based on high pre-stress compensation.The new negative Poisson’s ratio(NPR)bolt developed has the mechanical characteristics of high strength,high toughness,and impact resistance,serving as the material basis for the ECM.The field test results reveal that the ECM and the NPR bolt succeed in controlling rockburst disasters effectively.The research results are expected to provide guidance for rockburst support in deep underground projects such as Sichuan-Xizang Railway.展开更多
In recent years,the mine tunneling method and the new Austrian tunneling method have been considered the main theories of tunneling approaches in China.It is difficult for the traditional technique to overcome the lar...In recent years,the mine tunneling method and the new Austrian tunneling method have been considered the main theories of tunneling approaches in China.It is difficult for the traditional technique to overcome the large deformation problems imposed by complex geological conditions of mountain soft rock tunneling.Hence,the compensation excavation method has been proposed to solve this issue under the consideration that all damage in tunneling originates from the excavation.It uses supportive strategies to counteract the excavation effects successfully.This paper provides an overview of the fundamental ideas of the compensation excavation method,methodologies,and field applications.The scientific validity and feasibility of the compensation excavation method were investigated through the practical engineering study of the Muzhailing and Changning tunnels.展开更多
Each joint of hydraulic drive quadruped robot is driven by the hydraulic drive unit(HDU), and the contacting between the robot foot end and the ground is complex and variable, which increases the difficulty of force...Each joint of hydraulic drive quadruped robot is driven by the hydraulic drive unit(HDU), and the contacting between the robot foot end and the ground is complex and variable, which increases the difficulty of force control inevitably. In the recent years, although many scholars researched some control methods such as disturbance rejection control, parameter self-adaptive control, impedance control and so on, to improve the force control performance of HDU, the robustness of the force control still needs improving. Therefore, how to simulate the complex and variable load characteristics of the environment structure and how to ensure HDU having excellent force control performance with the complex and variable load characteristics are key issues to be solved in this paper. The force control system mathematic model of HDU is established by the mechanism modeling method, and the theoretical models of a novel force control compensation method and a load characteristics simulation method under different environment structures are derived, considering the dynamic characteristics of the load stiffness and the load damping under different environment structures. Then, simulation effects of the variable load stiffness and load damping under the step and sinusoidal load force are analyzed experimentally on the HDU force control performance test platform, which provides the foundation for the force control compensation experiment research. In addition, the optimized PID control parameters are designed to make the HDU have better force control performance with suitable load stiffness and load damping, under which the force control compensation method is introduced, and the robustness of the force control system with several constant load characteristics and the variable load characteristics respectively are comparatively analyzed by experiment. The research results indicate that if the load characteristics are known, the force control compensation method presented in this paper has positive compensation effects on the load characteristics variation, i.e., this method decreases the effects of the load characteristics variation on the force control performance and enhances the force control system robustness with the constant PID parameters, thereby, the online PID parameters tuning control method which is complex needs not be adopted. All the above research provides theoretical and experimental foundation for the force control method of the quadruped robot joints with high robustness.展开更多
In the practical application of pneumatic control devices, the nonlinearity of a pneumatic control valve become the main factor affecting the control effect, which comes mainly from the dynamic friction force. The dyn...In the practical application of pneumatic control devices, the nonlinearity of a pneumatic control valve become the main factor affecting the control effect, which comes mainly from the dynamic friction force. The dynamic friction inside the valve may cause hysteresis and a dead zone. In this paper, a dither compensation mechanism is proposed to reduce negative effects on the basis of analyzing the mechanism of friction force. The specific dither signal(using a sinusoidal signal) was superimposed on the control signal of the valve. Based on the relationship between the parameters of the dither signal and the inherent characteristics of the proportional servo valve, a parameter tuning method was proposed, which uses a displacement sensor to measure the maximum static friction inside the valve. According to the experimental results, the proper amplitude ranges are determined for different pressures. In order to get the optimal parameters of the dither signal, some dither compensation experiments have been carried out on different signal amplitude and gas pressure conditions. Optimal parameters are determined under two kinds of pressure conditions. Using tuning parameters the valve spool displacement experiment has been taken. From the experiment results, hysteresis of the proportional servo valve is significantly reduced. And through simulation and experiments, the cut-off frequency of the proportional valve has also been widened. Therefore after adding the dither signal, the static and dynamic characteristics of the proportional valve are both improved to a certain degree. This research proposes a parameter tuning method of dither signal, and the validity of the method is verified experimentally.展开更多
The delay compensation method plays an essential role in maintaining the stability and achieving accurate real-time hybrid simulation results. The effectiveness of various compensation methods in different test scenar...The delay compensation method plays an essential role in maintaining the stability and achieving accurate real-time hybrid simulation results. The effectiveness of various compensation methods in different test scenarios, however, needs to be quantitatively evaluated. In this study, four compensation methods (i.e., the polynomial extrapolation, the linear acceleration extrapolation, the inverse compensation and the adaptive inverse compensation) are selected and compared experimentally using a frequency evaluation index (FEI) method. The effectiveness of the FEI method is first verified through comparison with the discrete transfer fimction approach for compensation methods assuming constant delay. Incomparable advantage is further demonstrated for the FEI method when applied to adaptive compensation methods, where the discrete transfer function approach is difficult to implement. Both numerical simulation and laboratory tests with predefined displacements are conducted using sinusoidal signals and random signals as inputs. Findings from numerical simulation and experimental results demonstrate that the FEI method is an efficient and effective approach to compare the performance of different compensation methods, especially for those requiring adaptation of compensation parameters.展开更多
A novel fiber Bragg grating (FBG) sensor array system based on digital phase generated carrier (PGC) demodulation and reference compensation method is proposed and set up. Experimental results confirm that the dig...A novel fiber Bragg grating (FBG) sensor array system based on digital phase generated carrier (PGC) demodulation and reference compensation method is proposed and set up. Experimental results confirm that the digital PGC demodulation can be used for wavelength-division-multiplexed FBG sensor array and the reference compensation method can reduce the environmental interference by approximately 40 dB in the frequency range from 20 Hz to 2 kHz. The minimum detectable wavelength-shift of the sensor system is 1 × 10^-3 pm/Hz^1/2.展开更多
AIM To evaluate the influence of creatinine methodology on the performance of chronic kidney disease(CKD)-Epidemiology Collaboration Group-calculated estimated glomerular filtration rate(CKD-EPI-eGFR) for CKD diagnosi...AIM To evaluate the influence of creatinine methodology on the performance of chronic kidney disease(CKD)-Epidemiology Collaboration Group-calculated estimated glomerular filtration rate(CKD-EPI-eGFR) for CKD diagnosis/staging in a large cohort of diabetic patients. METHODS Fasting blood samples were taken from diabetic patients attending our clinic for their regular annual examination, including laboratory measurement of serum creatinine and eGFR.RESULTS Our results indicated an overall excellent agreement in CKD staging(kappa = 0.918) between the Jaffé serum creatinine-and enzymatic serum creatinine-based CKDEPI-eGFR, with 9% of discordant cases. As compared to the enzymatic creatinine, the majority of discordances(8%) were positive, i.e., associated with the more advanced CKD stage re-classification, whereas only 1% of cases were negatively discordant if Jaffé creatinine was used for eGFR calculation. A minor proportion of the discordant cases(3.5%) were re-classified into clinically relevant CKD stage indicating mildly to moderately decreased kidney function(< 60 m L/min per 1.73 m^2). Significant acute and chronic hyperglycaemia, assessedas plasma glucose and Hb A1 c levels far above the recommended glycaemic goals, was associated with positively discordant cases. Due to a very low frequency, positive discordance is not likely to present a great burden for the health-care providers, while intensified medical care may actually be beneficial for the small number of discordant patients. On the other hand, a very low proportion of negatively discordant cases(1%) at the 60 m L/min per 1.73 m^2 eGFR level indicate a negligible possibility to miss the CKD diagnosis, which could be the most prominent clinical problem affecting patient care, considering high risk of CKD for adverse patient outcomes. CONCLUSION This study indicate that compensated Jaffé creatinine procedure, in spite of the glucose-dependent bias, is not inferior to enzymatic creatinine in CKD diagnosis/staging and therefore may provide a reliable and cost-effective tool for the renal function assessment in diabetic patients.展开更多
Based on particle-in-cell simulation, we studied the motions of ions and electrons. The results have shown that electrons are bounded by a magnetic field and only a small number of electrons can pass through the whirl...Based on particle-in-cell simulation, we studied the motions of ions and electrons. The results have shown that electrons are bounded by a magnetic field and only a small number of electrons can pass through the whirler channel. The plasma becomes non-neutral when it is emitted from the whirler, and the spatial charge leads to a beam divergence, which is unfavorable for mass separation. In order to compensate the spatial charge, a cathode is designed to transmit electrons and the quasi-neutral plasma beam. Experiment results have demonstrated that the auxiliary cathode can obviously improve the compensation degree of the spatial charge.展开更多
The number of wireless electronic gadgets used in mobile communication, vehicle collision avoidance system, compact radars, etc. is extremely increasing at a rapid rate. Thus, the characteristics of the antennas invol...The number of wireless electronic gadgets used in mobile communication, vehicle collision avoidance system, compact radars, etc. is extremely increasing at a rapid rate. Thus, the characteristics of the antennas involved in these gadgets are to be designed very stringently so as to avoid interferences & coupling and to improve compatibility, susceptibility, etc. Compact smart antenna with improved performance is highly essential to meet this challenging scenario. Mutual coupling between various elements of an array is one of the main factors which can be considered for improvement of performance of the antenna. Influence of mutual coupling on performance of the antenna is considered in this paper and various techniques to minimize this effect are presented. Effect of mutual coupling on radiation characteristics of the antenna can be compensated employing various methods like Conventional Mutual Impedance (CMI), Receiving Mutual Impedance (RMI). Analysis is presented as comparison between the two methods for different number of elements in the array. Analysis is also presented for different geometries of the array like circular and elliptical for improved performance. The results show performance improvement in the proposed array for parameters like SNR and Speed of convergence.展开更多
目的核算2018年上海市预防服务费用,分析公共卫生的投入与补偿模式,提出针对性的对策建议。方法基于卫生费用核算体系2011(System of Health Accounts 2011 Edition,SHA 2011),核算并阐述上海市预防服务费用的基本情况、功能配置、筹资...目的核算2018年上海市预防服务费用,分析公共卫生的投入与补偿模式,提出针对性的对策建议。方法基于卫生费用核算体系2011(System of Health Accounts 2011 Edition,SHA 2011),核算并阐述上海市预防服务费用的基本情况、功能配置、筹资补偿和机构流向。基于样本机构,梳理公共卫生投入及补偿情况。结果上海市预防服务总费用为151.66亿元,占经常性卫生费用的7.61%,人均预防服务费用为625.72元。预防服务费用主要用于其他项目、健康体检、免疫规划和慢性病管理等项目;主要发生在医院、基层医疗卫生机构和公共卫生机构,分别占47.24%、36.60%和16.16%;筹资来源以政府方案、家庭卫生支出和企业筹资方案为主。结论预防服务提供成本难以准确衡量,需从源头把控数据填报质量,加强核算数据精确性。公立医院公共卫生的投入与补偿需进一步明确政府责任,完善机制建设,稳步推进“医防融合”模式转变。展开更多
In this paper, we combine the method of constructing the compensating function introduced by Kawashima and the standard energy method for the study on the Landau equation with external forcing. Both the global existen...In this paper, we combine the method of constructing the compensating function introduced by Kawashima and the standard energy method for the study on the Landau equation with external forcing. Both the global existence of solutions near the time asymptotic states which are local Maxwellians and the optimal convergence rates are obtained. The method used here has its own advantage for this kind of studies because it does not involve the spectrum analysis of the corresponding linearized operator.展开更多
This paper deals with numerical solutions of nonlinear stiff stochastic differential equations with jump-diffusion and piecewise continuous arguments.By combining compensated split-step methods and balanced methods,a ...This paper deals with numerical solutions of nonlinear stiff stochastic differential equations with jump-diffusion and piecewise continuous arguments.By combining compensated split-step methods and balanced methods,a class of compensated split-step balanced(CSSB)methods are suggested for solving the equations.Based on the one-sided Lipschitz condition and local Lipschitz condition,a strong convergence criterion of CSSB methods is derived.It is proved under some suitable conditions that the numerical solutions produced by CSSB methods can preserve the mean-square exponential stability of the corresponding analytical solutions.Several numerical examples are presented to illustrate the obtained theoretical results and the effectiveness of CSSB methods.Moreover,in order to show the computational advantage of CSSB methods,we also give a numerical comparison with the adapted split-step backward Euler methods with or without compensation and tamed explicit methods.展开更多
The structure of a microlens array( MLA) can be formed on copper by an indentation process which is a new manufacture approach we applied here instead of a traditional method to test the material property,thereby wo...The structure of a microlens array( MLA) can be formed on copper by an indentation process which is a new manufacture approach we applied here instead of a traditional method to test the material property,thereby work time can be saved. Single-indentation and multi-indentation are both conducted to generate a single dimple and dimples array,namely micro lens and MLA. Based on finite element simulation method,factors affecting the form accuracy,such as springback at the compressed area of one single dimple and compressional deformation at the adjacent area of dimples arrays,are determined,and the results are verified by experiments under the same conditions. Meanwhile,indenter compensation method is proposed to improve form accuracy of single dimple,and the relationship between pitch and compressional deformation is investigated by modelling seven sets of multi-indentations at different pitches to identify the critical pitch for the MLA's indentation processing. Loads and cross-sectional profiles are measured and analyzed to reveal the compressional deformation mechanism. Finally,it is found that MLA at pitches higher than 1. 47 times of its diameter can be manufactured precisely by indentation using a compensated indenter.展开更多
We show a useful analytical method to design grating compensated dispersion-managed systems. Our method is in good agreement with the numerical results even in the presence of group delay ripples in the chirped fiber ...We show a useful analytical method to design grating compensated dispersion-managed systems. Our method is in good agreement with the numerical results even in the presence of group delay ripples in the chirped fiber gratings.展开更多
GFFs with less than 0.4 dB peak-to-peak error functions are routinely fabricated using commercially available coating machines by utilizing the natural error compensation mechanism of wavelength variable turning point...GFFs with less than 0.4 dB peak-to-peak error functions are routinely fabricated using commercially available coating machines by utilizing the natural error compensation mechanism of wavelength variable turning point optical monitoring method.展开更多
When the swath of Synthetic Aperture Sonar(SAS) is considerably wide, the spacevariant effect of motion errors becomes remarkable. This space-variant effect makes Displace Phase Center Algorithm(DPCA) invalid. To ...When the swath of Synthetic Aperture Sonar(SAS) is considerably wide, the spacevariant effect of motion errors becomes remarkable. This space-variant effect makes Displace Phase Center Algorithm(DPCA) invalid. To solve the problem, a motion compensation method for wide-swath SAS is proposed. This method uses mixed modulated Lagrange explicit time delay estimation(MMLETDE) to estimate the time delay between two successive pings of the raw echo data, and then motion errors are fitted by linear regression. After that, the raw echo data can be precisely compensated point by point with the estimations of motion errors.Simulation results show that the proposed method can obtain better motion estimation results than DPCA. The resolution measured on the reconstructed image processed by the proposed method is very close to the theoretical resolution. The lake trail results of high frequency and low frequency SAS data show that the quality of the images of the terrain area and small targets is significantly improved.展开更多
Regarding the rapid compensation of the influence of the Earth' s disturbing gravity field upon trajectory calculation,the key point lies in how to derive the analytical solutions to the partial derivatives of the st...Regarding the rapid compensation of the influence of the Earth' s disturbing gravity field upon trajectory calculation,the key point lies in how to derive the analytical solutions to the partial derivatives of the state of burnout point with respect to the launch data.In view of this,this paper mainly expounds on two issues:one is based on the approximate analytical solution to the motion equation for the vacuum flight section of a long-range rocket,deriving the analytical solutions to the partial derivatives of the state of burnout point with respect to the changing rate of the finalstage pitch program;the other is based on the initial positioning and orientation error propagation mechanism,proposing the analytical calculation formula for the partial derivatives of the state of burnout point with respect to the launch azimuth.The calculation results of correction data are simulated and verified under different circumstances.The simulation results are as follows:(1) the accuracy of approximation between the analytical solutions and the results attained via the difference method is higher than 90%,and the ratio of calculation time between them is lower than 0.2%,thus demonstrating the accuracy of calculation of data corrections and advantages in calculation speed;(2) after the analytical solutions are compensated,the longitudinal landing deviation of the rocket is less than 20 m and the lateral landing deviation of the rocket is less than 10 m,demonstrating that the corrected data can meet the requirements for the hit accuracy of a long-range rocket.展开更多
A novel compensation method for temperature-dependent gain tilt of L-band erbium-doped fiber amplifier (L-EDFA) is proposed, in which the attenuation between stages is the only parameter to be adjusted. A simple linea...A novel compensation method for temperature-dependent gain tilt of L-band erbium-doped fiber amplifier (L-EDFA) is proposed, in which the attenuation between stages is the only parameter to be adjusted. A simple linear relationship between the attenuation and the erbium fiber coil temperature was derived theoretically. When the erbium fiber coil temperature cycles from 26 to 70C, the gain tilt variation less than 0.3 dB is achieved experimentally by adjusting only the pre-inserted variable optical attenuator (VOA).展开更多
基金supported by the National Key Research and Development Plan(2018YFB1201601-12)。
文摘Due to unreliable and bandwidth-limited characteristics of communication link in networked control systems,the realtime compensated methods for single-output systems and multioutput systems are proposed in this paper based on the compressed sensing(CS)theory and sliding window technique,by which the estimates of dropping data packets in the feedback channel are obtained and the performance degradation induced by packet drops is reduced.Specifically,in order to reduce the cumulative error caused by the algorithm,the compensated estimates for single-output systems are corrected via the regularization term;considering the process of single-packet transmission,a new sequential CS framework of sensor data streams is introduced to effectively compensate the dropping packet on single-channel of multi-output systems;in presence of the medium access constraints on multi-channel,the communication sequence for scheduling is coupled to the algorithm and the estimates of the multiple sensors for multi-output systems are obtained via the regularization term.Simulation results illustrate that the proposed methods perform well and receive satisfactory performance.
基金supported by the Innovation Fund Research Project of State Key Laboratory for Geomechanics and Deep Underground Engineering,China University of Mining and Technology(Grant No.SKLGDUEK202201)the Foundation for the Opening of State Key Laboratory for Geomechanics and Deep Underground Engineering,China University of Mining and Technology(Grant No.SKLGDUEK2129)the Open Research Fund of State Key Laboratory of Geomechanics and Geotechnical Engineering,Institute of Rock and Soil Mechanics,Chinese Academy of Sciences(Grant No.Z020007)。
文摘In recent years,there is a scenario in urban tunnel constructions to build super-large-span tunnels for traffic diversion and route optimization purposes.However,the increased size makes tunnel support more difficult.Unfortunately,there are few studies on the failure and support mechanism of the surrounding rocks in the excavation of supported tunnel,while most model tests of super-large-span tunnels focus on the failure characteristics of surrounding rocks in tunnel excavation without supports.Based on excavation compensation method(ECM),model tests of a super-large-span tunnel excavation by different anchor cable support methods in the initial support stage were carried out.The results indicate that during excavation of super-large-span tunnel,the stress and displacement of the shallow surrounding rocks decrease,following a step-shape pattern,and the tunnel failure is mainly concentrated on the vault and spandrel areas.Compared with conventional anchor cable supports,the NPR(negative Poisson’s ratio)anchor cable support is more suitable for the initial support stage of the super-large-span tunnels.The tunnel support theory,model test materials,methods,and the results obtained in this study could provide references for study of similar super-large-span tunnels。
基金supported by the National Natural Science Foundation of China (41941018)the Foundation of State Key Laboratory for Geomechanics and Deep Underground Engineering (SKLGDUEK 2217)the Foundation of Collaborative Innovation Center for Prevention and Control of Mountain Geological Hazards of Zhejiang Province (PCMGH-2022-03).
文摘Rockburst disasters occur frequently during deep underground excavation,yet traditional concepts and methods can hardly meet the requirements for support under high geo-stress conditions.Consequently,rockburst control remains challenging in the engineering field.In this study,the mechanism of excavation-induced rockburst was briefly described,and it was proposed to apply the excavation compensation method(ECM)to rockburst control.Moreover,a field test was carried out on the Qinling Water Conveyance Tunnel.The following beneficial findings were obtained:Excavation leads to changes in the engineering stress state of surrounding rock and results in the generation of excess energy DE,which is the fundamental cause of rockburst.The ECM,which aims to offset the deep excavation effect and lower the risk of rockburst,is an active support strategy based on high pre-stress compensation.The new negative Poisson’s ratio(NPR)bolt developed has the mechanical characteristics of high strength,high toughness,and impact resistance,serving as the material basis for the ECM.The field test results reveal that the ECM and the NPR bolt succeed in controlling rockburst disasters effectively.The research results are expected to provide guidance for rockburst support in deep underground projects such as Sichuan-Xizang Railway.
基金The authors would like to acknowledge the financial support from the Key Special Project of the National Natural Science Foundation of China(No.41941018)the Special Fund of Yueqi Scholars(No.800015Z1207).
文摘In recent years,the mine tunneling method and the new Austrian tunneling method have been considered the main theories of tunneling approaches in China.It is difficult for the traditional technique to overcome the large deformation problems imposed by complex geological conditions of mountain soft rock tunneling.Hence,the compensation excavation method has been proposed to solve this issue under the consideration that all damage in tunneling originates from the excavation.It uses supportive strategies to counteract the excavation effects successfully.This paper provides an overview of the fundamental ideas of the compensation excavation method,methodologies,and field applications.The scientific validity and feasibility of the compensation excavation method were investigated through the practical engineering study of the Muzhailing and Changning tunnels.
基金Supported by National Key Basic Research Program of China(973 Program,Grant No.2014CB046405)State Key Laboratory of Fluid Power and Mechatronic Systems(Zhejiang University)Open Fund Project(Grant No.GZKF-201502)Hebei Military and Civilian Industry Development Funds Projects of China(Grant No.2015B060)
文摘Each joint of hydraulic drive quadruped robot is driven by the hydraulic drive unit(HDU), and the contacting between the robot foot end and the ground is complex and variable, which increases the difficulty of force control inevitably. In the recent years, although many scholars researched some control methods such as disturbance rejection control, parameter self-adaptive control, impedance control and so on, to improve the force control performance of HDU, the robustness of the force control still needs improving. Therefore, how to simulate the complex and variable load characteristics of the environment structure and how to ensure HDU having excellent force control performance with the complex and variable load characteristics are key issues to be solved in this paper. The force control system mathematic model of HDU is established by the mechanism modeling method, and the theoretical models of a novel force control compensation method and a load characteristics simulation method under different environment structures are derived, considering the dynamic characteristics of the load stiffness and the load damping under different environment structures. Then, simulation effects of the variable load stiffness and load damping under the step and sinusoidal load force are analyzed experimentally on the HDU force control performance test platform, which provides the foundation for the force control compensation experiment research. In addition, the optimized PID control parameters are designed to make the HDU have better force control performance with suitable load stiffness and load damping, under which the force control compensation method is introduced, and the robustness of the force control system with several constant load characteristics and the variable load characteristics respectively are comparatively analyzed by experiment. The research results indicate that if the load characteristics are known, the force control compensation method presented in this paper has positive compensation effects on the load characteristics variation, i.e., this method decreases the effects of the load characteristics variation on the force control performance and enhances the force control system robustness with the constant PID parameters, thereby, the online PID parameters tuning control method which is complex needs not be adopted. All the above research provides theoretical and experimental foundation for the force control method of the quadruped robot joints with high robustness.
基金Supported by National Natural Science Foundation of China(Grant No.51375045)the State Key Laboratory Program(Grant No.GZKF-201214)
文摘In the practical application of pneumatic control devices, the nonlinearity of a pneumatic control valve become the main factor affecting the control effect, which comes mainly from the dynamic friction force. The dynamic friction inside the valve may cause hysteresis and a dead zone. In this paper, a dither compensation mechanism is proposed to reduce negative effects on the basis of analyzing the mechanism of friction force. The specific dither signal(using a sinusoidal signal) was superimposed on the control signal of the valve. Based on the relationship between the parameters of the dither signal and the inherent characteristics of the proportional servo valve, a parameter tuning method was proposed, which uses a displacement sensor to measure the maximum static friction inside the valve. According to the experimental results, the proper amplitude ranges are determined for different pressures. In order to get the optimal parameters of the dither signal, some dither compensation experiments have been carried out on different signal amplitude and gas pressure conditions. Optimal parameters are determined under two kinds of pressure conditions. Using tuning parameters the valve spool displacement experiment has been taken. From the experiment results, hysteresis of the proportional servo valve is significantly reduced. And through simulation and experiments, the cut-off frequency of the proportional valve has also been widened. Therefore after adding the dither signal, the static and dynamic characteristics of the proportional valve are both improved to a certain degree. This research proposes a parameter tuning method of dither signal, and the validity of the method is verified experimentally.
基金National Natural Science Foundation of China under Grant No.51378107the Fundamental Research Funds for the Central Universities and Priority Academic Program Development of Jiangsu Higher Education Institutions under Grant No.KYLX-0158the National Natural Science Foundation under Grant No.CMMI-1227962
文摘The delay compensation method plays an essential role in maintaining the stability and achieving accurate real-time hybrid simulation results. The effectiveness of various compensation methods in different test scenarios, however, needs to be quantitatively evaluated. In this study, four compensation methods (i.e., the polynomial extrapolation, the linear acceleration extrapolation, the inverse compensation and the adaptive inverse compensation) are selected and compared experimentally using a frequency evaluation index (FEI) method. The effectiveness of the FEI method is first verified through comparison with the discrete transfer fimction approach for compensation methods assuming constant delay. Incomparable advantage is further demonstrated for the FEI method when applied to adaptive compensation methods, where the discrete transfer function approach is difficult to implement. Both numerical simulation and laboratory tests with predefined displacements are conducted using sinusoidal signals and random signals as inputs. Findings from numerical simulation and experimental results demonstrate that the FEI method is an efficient and effective approach to compare the performance of different compensation methods, especially for those requiring adaptation of compensation parameters.
基金supported by the National 863 Program under Grant No. 2007AA03Z415.
文摘A novel fiber Bragg grating (FBG) sensor array system based on digital phase generated carrier (PGC) demodulation and reference compensation method is proposed and set up. Experimental results confirm that the digital PGC demodulation can be used for wavelength-division-multiplexed FBG sensor array and the reference compensation method can reduce the environmental interference by approximately 40 dB in the frequency range from 20 Hz to 2 kHz. The minimum detectable wavelength-shift of the sensor system is 1 × 10^-3 pm/Hz^1/2.
文摘AIM To evaluate the influence of creatinine methodology on the performance of chronic kidney disease(CKD)-Epidemiology Collaboration Group-calculated estimated glomerular filtration rate(CKD-EPI-eGFR) for CKD diagnosis/staging in a large cohort of diabetic patients. METHODS Fasting blood samples were taken from diabetic patients attending our clinic for their regular annual examination, including laboratory measurement of serum creatinine and eGFR.RESULTS Our results indicated an overall excellent agreement in CKD staging(kappa = 0.918) between the Jaffé serum creatinine-and enzymatic serum creatinine-based CKDEPI-eGFR, with 9% of discordant cases. As compared to the enzymatic creatinine, the majority of discordances(8%) were positive, i.e., associated with the more advanced CKD stage re-classification, whereas only 1% of cases were negatively discordant if Jaffé creatinine was used for eGFR calculation. A minor proportion of the discordant cases(3.5%) were re-classified into clinically relevant CKD stage indicating mildly to moderately decreased kidney function(< 60 m L/min per 1.73 m^2). Significant acute and chronic hyperglycaemia, assessedas plasma glucose and Hb A1 c levels far above the recommended glycaemic goals, was associated with positively discordant cases. Due to a very low frequency, positive discordance is not likely to present a great burden for the health-care providers, while intensified medical care may actually be beneficial for the small number of discordant patients. On the other hand, a very low proportion of negatively discordant cases(1%) at the 60 m L/min per 1.73 m^2 eGFR level indicate a negligible possibility to miss the CKD diagnosis, which could be the most prominent clinical problem affecting patient care, considering high risk of CKD for adverse patient outcomes. CONCLUSION This study indicate that compensated Jaffé creatinine procedure, in spite of the glucose-dependent bias, is not inferior to enzymatic creatinine in CKD diagnosis/staging and therefore may provide a reliable and cost-effective tool for the renal function assessment in diabetic patients.
基金supported by National Natural Science Foundation of China(No.51177020)
文摘Based on particle-in-cell simulation, we studied the motions of ions and electrons. The results have shown that electrons are bounded by a magnetic field and only a small number of electrons can pass through the whirler channel. The plasma becomes non-neutral when it is emitted from the whirler, and the spatial charge leads to a beam divergence, which is unfavorable for mass separation. In order to compensate the spatial charge, a cathode is designed to transmit electrons and the quasi-neutral plasma beam. Experiment results have demonstrated that the auxiliary cathode can obviously improve the compensation degree of the spatial charge.
文摘The number of wireless electronic gadgets used in mobile communication, vehicle collision avoidance system, compact radars, etc. is extremely increasing at a rapid rate. Thus, the characteristics of the antennas involved in these gadgets are to be designed very stringently so as to avoid interferences & coupling and to improve compatibility, susceptibility, etc. Compact smart antenna with improved performance is highly essential to meet this challenging scenario. Mutual coupling between various elements of an array is one of the main factors which can be considered for improvement of performance of the antenna. Influence of mutual coupling on performance of the antenna is considered in this paper and various techniques to minimize this effect are presented. Effect of mutual coupling on radiation characteristics of the antenna can be compensated employing various methods like Conventional Mutual Impedance (CMI), Receiving Mutual Impedance (RMI). Analysis is presented as comparison between the two methods for different number of elements in the array. Analysis is also presented for different geometries of the array like circular and elliptical for improved performance. The results show performance improvement in the proposed array for parameters like SNR and Speed of convergence.
文摘目的核算2018年上海市预防服务费用,分析公共卫生的投入与补偿模式,提出针对性的对策建议。方法基于卫生费用核算体系2011(System of Health Accounts 2011 Edition,SHA 2011),核算并阐述上海市预防服务费用的基本情况、功能配置、筹资补偿和机构流向。基于样本机构,梳理公共卫生投入及补偿情况。结果上海市预防服务总费用为151.66亿元,占经常性卫生费用的7.61%,人均预防服务费用为625.72元。预防服务费用主要用于其他项目、健康体检、免疫规划和慢性病管理等项目;主要发生在医院、基层医疗卫生机构和公共卫生机构,分别占47.24%、36.60%和16.16%;筹资来源以政府方案、家庭卫生支出和企业筹资方案为主。结论预防服务提供成本难以准确衡量,需从源头把控数据填报质量,加强核算数据精确性。公立医院公共卫生的投入与补偿需进一步明确政府责任,完善机制建设,稳步推进“医防融合”模式转变。
基金supported by Strategic Research Grant of City University of Hong Kong, 7002129the Changjiang Scholar Program of Chinese Educational Ministry in Shanghai Jiao Tong University+1 种基金The research of the second author was supported partially by NSFC (10601018)partially by FANEDD
文摘In this paper, we combine the method of constructing the compensating function introduced by Kawashima and the standard energy method for the study on the Landau equation with external forcing. Both the global existence of solutions near the time asymptotic states which are local Maxwellians and the optimal convergence rates are obtained. The method used here has its own advantage for this kind of studies because it does not involve the spectrum analysis of the corresponding linearized operator.
基金supported by National Natural Science Foundation of China(Grant No.11971010)Scientific Research Project of Education Department of Hubei Province(Grant No.B2019184)。
文摘This paper deals with numerical solutions of nonlinear stiff stochastic differential equations with jump-diffusion and piecewise continuous arguments.By combining compensated split-step methods and balanced methods,a class of compensated split-step balanced(CSSB)methods are suggested for solving the equations.Based on the one-sided Lipschitz condition and local Lipschitz condition,a strong convergence criterion of CSSB methods is derived.It is proved under some suitable conditions that the numerical solutions produced by CSSB methods can preserve the mean-square exponential stability of the corresponding analytical solutions.Several numerical examples are presented to illustrate the obtained theoretical results and the effectiveness of CSSB methods.Moreover,in order to show the computational advantage of CSSB methods,we also give a numerical comparison with the adapted split-step backward Euler methods with or without compensation and tamed explicit methods.
基金Supported by the National Natural Science Foundation of China(51375050)
文摘The structure of a microlens array( MLA) can be formed on copper by an indentation process which is a new manufacture approach we applied here instead of a traditional method to test the material property,thereby work time can be saved. Single-indentation and multi-indentation are both conducted to generate a single dimple and dimples array,namely micro lens and MLA. Based on finite element simulation method,factors affecting the form accuracy,such as springback at the compressed area of one single dimple and compressional deformation at the adjacent area of dimples arrays,are determined,and the results are verified by experiments under the same conditions. Meanwhile,indenter compensation method is proposed to improve form accuracy of single dimple,and the relationship between pitch and compressional deformation is investigated by modelling seven sets of multi-indentations at different pitches to identify the critical pitch for the MLA's indentation processing. Loads and cross-sectional profiles are measured and analyzed to reveal the compressional deformation mechanism. Finally,it is found that MLA at pitches higher than 1. 47 times of its diameter can be manufactured precisely by indentation using a compensated indenter.
文摘We show a useful analytical method to design grating compensated dispersion-managed systems. Our method is in good agreement with the numerical results even in the presence of group delay ripples in the chirped fiber gratings.
文摘GFFs with less than 0.4 dB peak-to-peak error functions are routinely fabricated using commercially available coating machines by utilizing the natural error compensation mechanism of wavelength variable turning point optical monitoring method.
基金supported by the National Natural Science Foundation of China(11204343)the National High Technology Research and Development Program of China(863 Program)(2013AA092701)
文摘When the swath of Synthetic Aperture Sonar(SAS) is considerably wide, the spacevariant effect of motion errors becomes remarkable. This space-variant effect makes Displace Phase Center Algorithm(DPCA) invalid. To solve the problem, a motion compensation method for wide-swath SAS is proposed. This method uses mixed modulated Lagrange explicit time delay estimation(MMLETDE) to estimate the time delay between two successive pings of the raw echo data, and then motion errors are fitted by linear regression. After that, the raw echo data can be precisely compensated point by point with the estimations of motion errors.Simulation results show that the proposed method can obtain better motion estimation results than DPCA. The resolution measured on the reconstructed image processed by the proposed method is very close to the theoretical resolution. The lake trail results of high frequency and low frequency SAS data show that the quality of the images of the terrain area and small targets is significantly improved.
文摘Regarding the rapid compensation of the influence of the Earth' s disturbing gravity field upon trajectory calculation,the key point lies in how to derive the analytical solutions to the partial derivatives of the state of burnout point with respect to the launch data.In view of this,this paper mainly expounds on two issues:one is based on the approximate analytical solution to the motion equation for the vacuum flight section of a long-range rocket,deriving the analytical solutions to the partial derivatives of the state of burnout point with respect to the changing rate of the finalstage pitch program;the other is based on the initial positioning and orientation error propagation mechanism,proposing the analytical calculation formula for the partial derivatives of the state of burnout point with respect to the launch azimuth.The calculation results of correction data are simulated and verified under different circumstances.The simulation results are as follows:(1) the accuracy of approximation between the analytical solutions and the results attained via the difference method is higher than 90%,and the ratio of calculation time between them is lower than 0.2%,thus demonstrating the accuracy of calculation of data corrections and advantages in calculation speed;(2) after the analytical solutions are compensated,the longitudinal landing deviation of the rocket is less than 20 m and the lateral landing deviation of the rocket is less than 10 m,demonstrating that the corrected data can meet the requirements for the hit accuracy of a long-range rocket.
文摘A novel compensation method for temperature-dependent gain tilt of L-band erbium-doped fiber amplifier (L-EDFA) is proposed, in which the attenuation between stages is the only parameter to be adjusted. A simple linear relationship between the attenuation and the erbium fiber coil temperature was derived theoretically. When the erbium fiber coil temperature cycles from 26 to 70C, the gain tilt variation less than 0.3 dB is achieved experimentally by adjusting only the pre-inserted variable optical attenuator (VOA).