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| 1 | Autonomous planning and control strategy for space manipulators with dynamics uncertainty based on learning from demonstrations显示文摘Autonomous planning is a significant development direction of the space manipulator,and learning from demonstrations(LfD)is a potential strategy for complex tasks in the field.However,separating control from planning may cause large torque fluctuations and energy consumptions,even instability or danger in control of space manipulators,especially for the planning based on the human demonstrations.Therefore,we present an autonomous planning and control strategy for space manipulators based on LfD and focus on the dynamics uncertainty problem,a common problem of actual manipulators.The process can be divided into three stages:firstly,we reproduced the stochastic directed trajectory based on the Gaussian process-based LfD;secondly,we built the model of the stochastic dynamics of the actual manipulator with Gaussian process;thirdly,we designed an optimal controller based on the dynamics model to obtain the improved commanded torques and trajectory,and used the separation theorem to deal with stochastic characteristics during control.We evaluated the strategy with locating pre-screwed bolts experiment by Tiangong-2 manipulator system on the ground.The result showed that,compared with other strategies,the strategy proposed in this paper could significantly reduce torque fluctuations and energy consumptions,and its precision can meet the task requirements. | LI ChongYang LI ZhiQi JIANG ZaiNan CUI ShiPeng LIU Hong CAI HeGao | 2021 | Science China(Technological Sciences)2021，64，12： | 1 |
| 2 | Mechanical design and analysis of a novel variable stiffness actuator with symmetrical pivot adjustment显示文摘The safety of human-robot interaction is an essential requirement for designing collaborative robotics.Thus,this paper aims to design a novel variable stiffiiess actuator(VSA)that can provide safer physical human-robot interaction for collaborative robotics.VS A follows the idea of modular design,mainly including a variable stiffiiess module and a drive module.The variable stiffiiess module transmits the motion from the drive module in a roundabout maimer,making the modularization of VS A possible.As the key component of the variable stiffiiess module,a stiffness adjustment mechanism with a symmetrical structure is applied to change the positions of a pair of pivots in two levers linearly and simultaneously,which can eliminate the additional bending moment caused by the asymmetric structure.The design of the doubledeck grooves in the lever allows the pivot to move freely in the groove,avoiding the geometric constraint between the parts.Consequently,the VSA stiffiiess can change from zero to infinity as the pivot moves from one end of the groove to the other.To facilitate building a manipulator in the future,an expandable electrical system with a distributed structure is also proposed.Stiffiiess calibration and control experiments are performed to evaluate the physical performance of the designed VSA.Experiment results show that the VSA stiffiiess is close to the theoretical design stiffness.Furthermore,the VSA with a proportional-derivative feedback plus feedforward controller exhibits a fast response for stiffiiess regulation and a good performance for position tracking. | Yiwei LIU Shipeng CUI Yongjun SUN | 2021 | Frontiers of Mechanical Engineering2021，16，4： | 1 |
| 3 | Fault Diagnosis of the LAMOST Fiber Positioner Based on a Long Short-term Memory(LSTM)Deep Neural Network显示文摘The Large Sky Area Multi-Object Fiber Spectroscopic Telescope(LAMOST)has been in normal operation for more than 10 yr,and routine maintenance is performed on the fiber positioner every summer.The positioning accuracy of the fiber positioner directly affects the observation performance of LAMOST,and incorrect fiber positioner positioning accuracy will not only increase the interference probability of adjacent fiber positioners but also reduces the observation efficiency of LAMOST.At present,during the manual maintenance process of the positioner,the fault cause of the positioner is determined and analyzed when the positioning accuracy does not meet the preset requirements.This causes maintenance to take a long time,and the efficiency is low.To quickly locate the fault cause of the positioner,the repeated positioning accuracy and open-loop calibration curve data of each positioner are obtained in this paper through the photographic measurement method.Based on a systematic analysis of the operational characteristics of the faulty positioner,the fault causes are classified.After training a deep learning model based on long short-term memory,the positioner fault causes can be quickly located to effectively improve the efficiency of positioner fault cause analysis.The relevant data can also provide valuable information for annual routine maintenance methods and positioner designs in the future.The method of using a deep learning model to analyze positioner operation failures introduced in this paper is also of general significance for the maintenance and design optimization of fiber positioners using a similar double-turn gear transmission system. | Yihu Tang Yingfu Wang Shipeng Duan Jiadong Liang Zeyu Cai Zhigang Liu Hongzhuan Hu Jianping Wang Jiaru Chu Xiangqun Cui Yong Zhang Haotong Zhang Zengxiang Zhou | 2023 | Research in Astronomy and Astrophysics2023，23，12： | 0 |
| 4 | Effects of fiber orientation on tool wear evolution and wear mechanism when cutting carbon fiber reinforced plastics显示文摘The aim of the present paper is to reveal the influence of different fiber orientations on the tool wear evolution and wear mechanism. Side-milling experiments with large-diameter milling tools are conducted. A finite element(FE) cutting model of carbon fiber reinforced plastics(CFRP)is established to get insight into the cutting stress status at different wear stages. The results show that different fiber orientations bring about distinct differences in the extent, profile and mechanism of tool wear. Severer wear occurs when cutting 45° and 90° plies, followed by 0°, correspondingly,the least wear is obtained when θ = 135°(θ represents the orientation of fibers). Moreover, the worn profiles of cutting tools when θ = 0° and 45° are waterfall edge, while round edge occurs whenθ = 135° and a combined shape of waterfall and round edge is obtained when θ = 90°. The wear mechanisms under different fiber orientations are strongly dependent on the cutting stress distributions. The evolution of tool wear profile is basically consistent with the stress distribution on the tool surface at different wear stages, and the extent of tool wear is determined by the magnitude of stress on the tool surface. Besides, the worn edges produce an actual negative clearance angle,which decreases the actual cutting thickness and leads to compressing and bending failure of fibers beneath the cutting region as well as low surface qualities. | Weizhou WU Shipeng LI Xuda QIN Wentao LIU Xin CUI Hao LI Mengrui SHI Haibao LIU | 2023 | Chinese Journal of Aeronautics2023，36，5： | 0 |
| 5 | The IDD Transcription Factors:Their Functions in Plant Development and Environmental Response显示文摘INDETERMINATE-DOMAIN proteins(IDDs)are a plant-specific transcription factor family characterized by a conserved ID domain with four zinc finger motifs.Previous studies have demonstrated that IDDs coordinate a diversity of physiological processes and functions in plant growth and development,including floral transition,plant architecture,seed and root development,and hormone signaling.In this review,we especially summarized the latest knowledge on the functions and working models of IDD members in Arabidopsis,rice,and maize,particularly focusing on their role in the regulatory network of biotic and abiotic environmental responses,such as gravity,temperature,water,and pathogens.Understanding these mechanisms underlying the function of IDD proteins in these processes is important for improving crop yields by manipulating their activity.Overall,the review offers valuable insights into the functions and mechanisms of IDD proteins in plants,providing a foundation for further research and potential applications in agriculture. | Jing Liu Defeng Shu Zilong Tan Mei Ma Huanhuan Yang Ning Guo Shipeng Li Dayong Cui | 2024 | Phyton-International Journal of Experimental Botany2024，93，1： | 0 |
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