Seven-degree-of-freedom redundant manipulators with link offset have many advantages,including obvious geometric significance and suitability for configuration control.Their configuration is similar to that of the exp...Seven-degree-of-freedom redundant manipulators with link offset have many advantages,including obvious geometric significance and suitability for configuration control.Their configuration is similar to that of the experimental module manipulator(EMM)in the Chinese Space Station Remote Manipulator System.However,finding the analytical solution of an EMM on the basis of arm angle parameterization is difficult.This study proposes a high-precision,semi-analytical inverse method for EMMs.Firstly,the analytical inverse kinematic solution is established based on joint angle parameterization.Secondly,the analytical inverse kinematic solution for a non-offset spherical-roll-spherical(SRS)redundant manipulator is derived based on arm angle parameterization.The approximate solution of the EMM is calculated in accordance with the relationship between the joint angles of the EMM and the SRS manipulator.Thirdly,the error is corrected using a numerical method through the analytical inverse solution based on joint angle parameterization.After selecting the stride and termination condition,the precise inverse solution is computed for the EMM based on arm angle parameterization.Lastly,case solutions confirm that this method has high precision,and the arm angle parameterization method is superior to the joint angle parameterization method in terms of parameter selection.展开更多
Plants develop branches to expand areas for assimilation and reproduction.Branching angles coordinate with branching types,creating diverse plant shapes that are adapted to various environments.Two types of branching ...Plants develop branches to expand areas for assimilation and reproduction.Branching angles coordinate with branching types,creating diverse plant shapes that are adapted to various environments.Two types of branching angle—the angle between shoots and the angle in relation to gravity or the gravitropic set-point angle(GSA)along shoots—determine the spacing between shoots and the shape of the aboveground plant parts.However,it remains unclear how these branching angles are modulated throughout shoot development and how they interact with other factors that contribute to plant architecture.In this review,we systematically focus on the molecular mechanisms that regulate branching angles across various spe-cies,including gravitropism,anti-gravitropic offset,phototropism,and other regulatory factors,which collectively highlight comprehensive mechanisms centered on auxin.We also discuss the dynamics of branching angles during development and their relationships with branching number,stress resistance,and crop yield.Finally,we provide an evolutionary perspective on the conserved role of auxin in the regu-lation of branching angles.展开更多
目的力角特性是永磁直线同步电机(permanent magnet linear synchronous motor,PMLSM)运行稳定性的重要特性,是评价电机性能和控制电机的依据。但在低频工况下,PMLSM的力角特性因电枢电阻的影响而存在偏移现象,进而导致利用现有忽略电...目的力角特性是永磁直线同步电机(permanent magnet linear synchronous motor,PMLSM)运行稳定性的重要特性,是评价电机性能和控制电机的依据。但在低频工况下,PMLSM的力角特性因电枢电阻的影响而存在偏移现象,进而导致利用现有忽略电枢电阻的力角特性分析计算电机低速运行特性会存在较大的偏差。为此,对PMLSM低频低速下的力角特性偏移原因及其影响规律展开深入研究,并确定力角特性偏移的临界条件。方法首先,建立考虑电枢电阻的PMLSM力角特性的解析模型,分析力角特性产生偏移的原因;其次,基于建立的解析模型,通过峰值推力及其对应的功角研究不同因素对推力特性的影响规律,并建立有限元模型对分析结果进行验证。然后,利用解析法确定PMLSM力角特性产生偏移的临界条件,即当力角偏移系数k(k=X_(t)/R_(a))≥11.43可以近似认为峰值推力对应的功角等于90°,可以忽略力角偏移现象;最后,搭建PMLSM样机测试平台,将有限元结果、实验结果与理论分析进行比较,验证推力特性曲线产生偏移的原因和临界条件。结果研究发现,与常用的忽略电枢电阻的力角特性相比,PMLSM力角特性向左偏移。力角特性偏移现象会导致两方面的影响,一是导致推力和电枢电流的关系不单调,出现小负载的电流比大负载的还要大的现象,二是低频运行时峰值推力减小,因此低频时不能保持恒推力运行。结论研究结果对PMLSM的设计和精确控制具有重要的参考价值。展开更多
基金This work was supported by the Foundation for Innovative Research Groups of the National Natural Science Foundation of China(Grant No.51521003)the Major Research Plan of National Natural Science Foundation of China(Grant No.91848202).
文摘Seven-degree-of-freedom redundant manipulators with link offset have many advantages,including obvious geometric significance and suitability for configuration control.Their configuration is similar to that of the experimental module manipulator(EMM)in the Chinese Space Station Remote Manipulator System.However,finding the analytical solution of an EMM on the basis of arm angle parameterization is difficult.This study proposes a high-precision,semi-analytical inverse method for EMMs.Firstly,the analytical inverse kinematic solution is established based on joint angle parameterization.Secondly,the analytical inverse kinematic solution for a non-offset spherical-roll-spherical(SRS)redundant manipulator is derived based on arm angle parameterization.The approximate solution of the EMM is calculated in accordance with the relationship between the joint angles of the EMM and the SRS manipulator.Thirdly,the error is corrected using a numerical method through the analytical inverse solution based on joint angle parameterization.After selecting the stride and termination condition,the precise inverse solution is computed for the EMM based on arm angle parameterization.Lastly,case solutions confirm that this method has high precision,and the arm angle parameterization method is superior to the joint angle parameterization method in terms of parameter selection.
基金supported by the Young Scientists Fund of the National Natural Science Foundation of China(No.61572004)the Chinese Universities Scientific Fund(No.2024TC162,No.2024RC030,No.2023RC004)+1 种基金the Pinduoduo-China Agricultural University Research Fund(No.PC2023B02003)the 2115 Talent Development Program of China Agricultural University to L.L.
文摘Plants develop branches to expand areas for assimilation and reproduction.Branching angles coordinate with branching types,creating diverse plant shapes that are adapted to various environments.Two types of branching angle—the angle between shoots and the angle in relation to gravity or the gravitropic set-point angle(GSA)along shoots—determine the spacing between shoots and the shape of the aboveground plant parts.However,it remains unclear how these branching angles are modulated throughout shoot development and how they interact with other factors that contribute to plant architecture.In this review,we systematically focus on the molecular mechanisms that regulate branching angles across various spe-cies,including gravitropism,anti-gravitropic offset,phototropism,and other regulatory factors,which collectively highlight comprehensive mechanisms centered on auxin.We also discuss the dynamics of branching angles during development and their relationships with branching number,stress resistance,and crop yield.Finally,we provide an evolutionary perspective on the conserved role of auxin in the regu-lation of branching angles.
文摘目的力角特性是永磁直线同步电机(permanent magnet linear synchronous motor,PMLSM)运行稳定性的重要特性,是评价电机性能和控制电机的依据。但在低频工况下,PMLSM的力角特性因电枢电阻的影响而存在偏移现象,进而导致利用现有忽略电枢电阻的力角特性分析计算电机低速运行特性会存在较大的偏差。为此,对PMLSM低频低速下的力角特性偏移原因及其影响规律展开深入研究,并确定力角特性偏移的临界条件。方法首先,建立考虑电枢电阻的PMLSM力角特性的解析模型,分析力角特性产生偏移的原因;其次,基于建立的解析模型,通过峰值推力及其对应的功角研究不同因素对推力特性的影响规律,并建立有限元模型对分析结果进行验证。然后,利用解析法确定PMLSM力角特性产生偏移的临界条件,即当力角偏移系数k(k=X_(t)/R_(a))≥11.43可以近似认为峰值推力对应的功角等于90°,可以忽略力角偏移现象;最后,搭建PMLSM样机测试平台,将有限元结果、实验结果与理论分析进行比较,验证推力特性曲线产生偏移的原因和临界条件。结果研究发现,与常用的忽略电枢电阻的力角特性相比,PMLSM力角特性向左偏移。力角特性偏移现象会导致两方面的影响,一是导致推力和电枢电流的关系不单调,出现小负载的电流比大负载的还要大的现象,二是低频运行时峰值推力减小,因此低频时不能保持恒推力运行。结论研究结果对PMLSM的设计和精确控制具有重要的参考价值。
