Aiming at a space manipulator with free-swinging joint failure, a failure treatment strategy and fault-tolerant path planning method is proposed in this paper. This method can realize failure treatment of a space mani...Aiming at a space manipulator with free-swinging joint failure, a failure treatment strategy and fault-tolerant path planning method is proposed in this paper. This method can realize failure treatment of a space manipulator with free-swinging joint failure through determination of the optimal locked joint angle and dynamics model reconfiguration. Fault-tolerant path planning is realized by the establishment of the degraded workspace with integrated kinematics performance(DWWIKP) and an improved A-Star(A*) algorithm. This paper has the following contributions.The determination of the optimal locked joint angle can ensure that the manipulator is able to continue follow-up tasks while maximizing the workspace of the manipulator after locking the fault joint. Underactuated control of a high degree-of-freedom(DOF) manipulator can be effectively solved through dynamics model reconfiguration. The analysis process of the dynamics coupling relationship can be applied to cases where the active joint and the passive joint are parallel or perpendicular to each other. The establishment of the DWWIKP can demonstrate the kinematics performance of the manipulator in both joint space and operation space comprehensively. The improved A*algorithm based on the integrated kinematics performance index(IKPI) can search a fault-tolerant task trajectory that satisfies the requirements of reachability and the overall kinematics performance simultaneously. The method proposed in this paper is verified by a 7-DOF manipulator, and it is available to any DOF manipulator with free-swinging joint failure.展开更多
Space robotics is regarded as one of the most impressing approaches for space debris removal missions. Due to the residual momentum of debris, it is essential to stabilize the base rapidly after capture. This paper pr...Space robotics is regarded as one of the most impressing approaches for space debris removal missions. Due to the residual momentum of debris, it is essential to stabilize the base rapidly after capture. This paper presents a novel control strategy for stabilization of a space robot in postcapture considering actuator failures and bounded torques. In the control strategy, the motion of the manipulator is not regarded as a disturbance to the base; in contrast, it is utilized to compensate for the limitation of the control torques by means of an inverse dynamical model of the system. Different scenarios where actuators are external mechanisms or momentum exchange devices have been carried out, and for actuator failures, both single-and two-actuator failures have been considered. Regarding to the performance of actuators, control torques are bounded. In cases that either single or two actuators have failed, the base can be stabilized kinematically when actuators are external mechanisms, but can only be stabilized dynamically when only momentum exchange devices are used. Finally, a space robot with a seven-degree-of-freedom manipulator in postcapture is studied to verify the validity and feasibility of the proposed control scheme. Simulation results show that the whole system can be stabilized rapidly.展开更多
Based on the micro-morphology theory, the authors set up a set of feature descriptors of debris, use it to abstract the characteristic information of wearing particles, and identify them by the auto clustering, Artifi...Based on the micro-morphology theory, the authors set up a set of feature descriptors of debris, use it to abstract the characteristic information of wearing particles, and identify them by the auto clustering, Artificial Neural Network (ANN) and other artificial intelligence (AI) means. The technique has found its application in the wearing fault diagnosis of aero-engines.展开更多
To ensure tasks can be completed after a free-swinging joint failure occurs,a multi-stage regulation strategy of space manipulators is proposed.Considering all terms of the dynamics equation,an evaluation model of the...To ensure tasks can be completed after a free-swinging joint failure occurs,a multi-stage regulation strategy of space manipulators is proposed.Considering all terms of the dynamics equation,an evaluation model of the regulation ability(EMRA)of active joints over the fault joint is established based on the fuzzy entropy.And then a multi-stage regulation strategy based on the EMRA is designed to regulate the fault joint.The strategy divides the regulation process into several stages,and select a certain active joint to regulative the fault joint in every stage.With this multi-stage regulation strategy,the fault joint can be regulated to the desired angle without huge torque on regulative joints.The simulation is carried out with a 7-DOF space manipulator,verifying the correctness and effectiveness of the multi-stage regulation strategy.The strategy has three advantages:Coriolis and centrifugal terms are both considered for the first time in selecting the regulative joint,making the selection result more in line with the actual regulation process;The influence of the model uncertainty is eliminated in establishing the EMRA,making the evaluation of regulative ability more precise;The fault joint is successfully regulated to the desired angle without huge torque on regulative joints.展开更多
系统关键故障的发生,会导致系统处于各种离散性能降级状态。针对传统的基于马尔可夫链蒙特卡罗(Markovchain Monte Carlo,MCMC)的自适应重要抽样法只适用于连续变量系统的不足,提出考虑混合变量的基于MCMC的自适应重要抽样法,以支持系...系统关键故障的发生,会导致系统处于各种离散性能降级状态。针对传统的基于马尔可夫链蒙特卡罗(Markovchain Monte Carlo,MCMC)的自适应重要抽样法只适用于连续变量系统的不足,提出考虑混合变量的基于MCMC的自适应重要抽样法,以支持系统性能可靠性的高效仿真。该方法首先将由关键故障产生的不同失效域组成失效空间,并通过初始样本点在失效空间中随机游走构造马尔可夫链模拟样本;然后综合考虑连续变量与离散变量,利用核密度估计构建混合核抽样密度函数;再根据该密度函数进行重要抽样仿真并计算系统的性能可靠性;最后对该方法的仿真效率进行理论分析。通过电液舵机(Electro-Hydrostatic Actuator,EHA)案例对方法的正确性和仿真效率进行验证。展开更多
Objective： To assess zero drift of intra- ventricular and subdural intracranial pressure （ICP） moni- toring systems. Methods： A prospective study was conducted in pa- tients who received Codman ICP monitoring in ...Objective： To assess zero drift of intra- ventricular and subdural intracranial pressure （ICP） moni- toring systems. Methods： A prospective study was conducted in pa- tients who received Codman ICP monitoring in the neuro- surgical department from January 2010 to December 2011. According to the location of sensors, the patients were ca- tegorized into two groups： intraventricular group and sub- dural group. Zero drift between the two groups and its as- sociation with the duration of ICP monitor were analyzed. Results： Totally, 22 patients undergoing intraven- tricular ICP monitoring and 27 receiving subdural ICP moni- toring were enrolled. There was no significant difference in duration of ICP monitoring, zero drift value and its absolute value between intraventricular and subdural groups （5.38 d± 2.58 d vs 4.58 d.±2.24 d, 0.77 mmHg±2.18 mmHg vs 1.03 mmHg±2.06mmHg, 1.68 mmHg~.l.55 mmHgvs 1.70mmHg.t_l.53 mmHg, respectively; all P〉0.05）. Absolute value of zero drift in both groups significantly rose with the increased duration of ICP monitoring （P〈0.05） while zero drift value did not. Moreover, daily absolute value in the intraventricular group was sig- nificantly smaller than that in the subdural group （0.27 mm Hg_＋ 0.32 mm Hg vs 0.29 mm Hg_-_＊0.18 mm Hg, P〈0.05）. Conclusion： This study demonstrates that absolute value of zero drift significantly correlates with duration of both intraventricular and subdural ICP monitoring. Due to the smaller daily absolute value, ICP values recorded from intraventficular system may be more reliable than those from subdural system.展开更多
基金co-supported by the National Nature Science Foundation of China(No.’s 61403038 and 61573066)the National Basic Research Program of China(No.2013CB733000)
文摘Aiming at a space manipulator with free-swinging joint failure, a failure treatment strategy and fault-tolerant path planning method is proposed in this paper. This method can realize failure treatment of a space manipulator with free-swinging joint failure through determination of the optimal locked joint angle and dynamics model reconfiguration. Fault-tolerant path planning is realized by the establishment of the degraded workspace with integrated kinematics performance(DWWIKP) and an improved A-Star(A*) algorithm. This paper has the following contributions.The determination of the optimal locked joint angle can ensure that the manipulator is able to continue follow-up tasks while maximizing the workspace of the manipulator after locking the fault joint. Underactuated control of a high degree-of-freedom(DOF) manipulator can be effectively solved through dynamics model reconfiguration. The analysis process of the dynamics coupling relationship can be applied to cases where the active joint and the passive joint are parallel or perpendicular to each other. The establishment of the DWWIKP can demonstrate the kinematics performance of the manipulator in both joint space and operation space comprehensively. The improved A*algorithm based on the integrated kinematics performance index(IKPI) can search a fault-tolerant task trajectory that satisfies the requirements of reachability and the overall kinematics performance simultaneously. The method proposed in this paper is verified by a 7-DOF manipulator, and it is available to any DOF manipulator with free-swinging joint failure.
基金co-supported by the National Natural Science Foundation of China (Nos. 11402200 and 11502203)the China Scholarship Council (CSC)
文摘Space robotics is regarded as one of the most impressing approaches for space debris removal missions. Due to the residual momentum of debris, it is essential to stabilize the base rapidly after capture. This paper presents a novel control strategy for stabilization of a space robot in postcapture considering actuator failures and bounded torques. In the control strategy, the motion of the manipulator is not regarded as a disturbance to the base; in contrast, it is utilized to compensate for the limitation of the control torques by means of an inverse dynamical model of the system. Different scenarios where actuators are external mechanisms or momentum exchange devices have been carried out, and for actuator failures, both single-and two-actuator failures have been considered. Regarding to the performance of actuators, control torques are bounded. In cases that either single or two actuators have failed, the base can be stabilized kinematically when actuators are external mechanisms, but can only be stabilized dynamically when only momentum exchange devices are used. Finally, a space robot with a seven-degree-of-freedom manipulator in postcapture is studied to verify the validity and feasibility of the proposed control scheme. Simulation results show that the whole system can be stabilized rapidly.
文摘Based on the micro-morphology theory, the authors set up a set of feature descriptors of debris, use it to abstract the characteristic information of wearing particles, and identify them by the auto clustering, Artificial Neural Network (ANN) and other artificial intelligence (AI) means. The technique has found its application in the wearing fault diagnosis of aero-engines.
基金co-supported by the Fundamental Research Funds for the Central Universities of China(No.2019PTB012)the Science and Technology Foundation of State Key Laboratory of China(No.6142210180302)the National Natural Science Foundation of China(No.51975059)。
文摘To ensure tasks can be completed after a free-swinging joint failure occurs,a multi-stage regulation strategy of space manipulators is proposed.Considering all terms of the dynamics equation,an evaluation model of the regulation ability(EMRA)of active joints over the fault joint is established based on the fuzzy entropy.And then a multi-stage regulation strategy based on the EMRA is designed to regulate the fault joint.The strategy divides the regulation process into several stages,and select a certain active joint to regulative the fault joint in every stage.With this multi-stage regulation strategy,the fault joint can be regulated to the desired angle without huge torque on regulative joints.The simulation is carried out with a 7-DOF space manipulator,verifying the correctness and effectiveness of the multi-stage regulation strategy.The strategy has three advantages:Coriolis and centrifugal terms are both considered for the first time in selecting the regulative joint,making the selection result more in line with the actual regulation process;The influence of the model uncertainty is eliminated in establishing the EMRA,making the evaluation of regulative ability more precise;The fault joint is successfully regulated to the desired angle without huge torque on regulative joints.
文摘系统关键故障的发生,会导致系统处于各种离散性能降级状态。针对传统的基于马尔可夫链蒙特卡罗(Markovchain Monte Carlo,MCMC)的自适应重要抽样法只适用于连续变量系统的不足,提出考虑混合变量的基于MCMC的自适应重要抽样法,以支持系统性能可靠性的高效仿真。该方法首先将由关键故障产生的不同失效域组成失效空间,并通过初始样本点在失效空间中随机游走构造马尔可夫链模拟样本;然后综合考虑连续变量与离散变量,利用核密度估计构建混合核抽样密度函数;再根据该密度函数进行重要抽样仿真并计算系统的性能可靠性;最后对该方法的仿真效率进行理论分析。通过电液舵机(Electro-Hydrostatic Actuator,EHA)案例对方法的正确性和仿真效率进行验证。
文摘Objective： To assess zero drift of intra- ventricular and subdural intracranial pressure （ICP） moni- toring systems. Methods： A prospective study was conducted in pa- tients who received Codman ICP monitoring in the neuro- surgical department from January 2010 to December 2011. According to the location of sensors, the patients were ca- tegorized into two groups： intraventricular group and sub- dural group. Zero drift between the two groups and its as- sociation with the duration of ICP monitor were analyzed. Results： Totally, 22 patients undergoing intraven- tricular ICP monitoring and 27 receiving subdural ICP moni- toring were enrolled. There was no significant difference in duration of ICP monitoring, zero drift value and its absolute value between intraventricular and subdural groups （5.38 d± 2.58 d vs 4.58 d.±2.24 d, 0.77 mmHg±2.18 mmHg vs 1.03 mmHg±2.06mmHg, 1.68 mmHg~.l.55 mmHgvs 1.70mmHg.t_l.53 mmHg, respectively; all P〉0.05）. Absolute value of zero drift in both groups significantly rose with the increased duration of ICP monitoring （P〈0.05） while zero drift value did not. Moreover, daily absolute value in the intraventricular group was sig- nificantly smaller than that in the subdural group （0.27 mm Hg_＋ 0.32 mm Hg vs 0.29 mm Hg_-_＊0.18 mm Hg, P〈0.05）. Conclusion： This study demonstrates that absolute value of zero drift significantly correlates with duration of both intraventricular and subdural ICP monitoring. Due to the smaller daily absolute value, ICP values recorded from intraventficular system may be more reliable than those from subdural system.
