Luffing mechanism is a key component of the construction machinery.This paper proposes a two degree of freedom(2-DOF)luffing mechanism,which has one more pair of driving cylinders than the single DOF luffing mechanism...Luffing mechanism is a key component of the construction machinery.This paper proposes a two degree of freedom(2-DOF)luffing mechanism,which has one more pair of driving cylinders than the single DOF luffing mechanism,to improve the performance of the machinery.To establish the dynamic model of the 2-DOF luffing mechanism,firstly,we develop a hierarchical method to deduce the Jacobian matrix and Hessian matrix for obtaining the kinematics equations.Subsequently,we divide the luffing mechanism into six bodies considering actuators,and deduce the kinetic equations of each body by the Newton-Euler method.Based on the dynamic model,we simulate the luffing process.Finally,a prototype is built on a pile driver to validate the model.Simulations and experiments show that the dynamic model can reflect the dynamic properties of the proposed luffing mechanism.And the control strategy that the front cylinders retract first shows better mechanical behavior than the other two control strategies.This research provides a reference for the design and application of 2-DOF luffing mechanism on construction machinery.The modeling approach can also be applied to similar mechanism with serial closed kinematic chains,which allows to calculate the dynamic parameters easily and exactly.展开更多
To introduce ordered nano-structures inside a transparent amorphous matrix with superior optical and mechanical properties bears scientific and technological importance,yet limited success has been achieved.Here,via s...To introduce ordered nano-structures inside a transparent amorphous matrix with superior optical and mechanical properties bears scientific and technological importance,yet limited success has been achieved.Here,via simple melting-quenching and subsequent thermal activation,we report the successful preparation of transparent nano-structured glass-ceramics embedded in Sr2Lu F7 nano-crystals(~26 nm),as evidenced by X-ray diffraction,transmission electron microscopy(TEM),and high resolution TEM.The successful incorporation of dopants into formed Sr2Lu F7 nano-crystals with low phonon energy results in highly tunable blue–green photoemission,which depends on excitation wavelength,dopant type,and temperature.We found that Eu3+and Eu2+ions co-exist in this hybrid optical material,accompanied by the broadband blue emission of Eu2+and sharp red emissions of Eu3+.A series of optical characterizations are summoned,including emission/excitation spectrum and decay curve measurement,to reveal the reduction mechanism of Eu3+to Eu2+.Furthermore,near green–white photoemission is achieved via the enrichment of Tb3+/Eu3+into crystallized Sr2Lu F7 nano-crystals.The temperature-dependent visible photoemission reveals thermal activation energy increases with the precipitation of Sr2Lu F7 nano-crystals in a glass matrix,suggesting better thermal stability of glass-ceramics than precursor glasses.These results could not only deepen the understanding of glass-ceramics but also indicate the promising potential of Eu3+/Tb3+-ions-doped Sr2Lu F7 glass-ceramics for UV pumped white light emitting diodes(WLEDs)with good thermal stability.展开更多
基金Project(2015B020238014)supported by the Science and Technology Program of Guangdong Province,China。
文摘Luffing mechanism is a key component of the construction machinery.This paper proposes a two degree of freedom(2-DOF)luffing mechanism,which has one more pair of driving cylinders than the single DOF luffing mechanism,to improve the performance of the machinery.To establish the dynamic model of the 2-DOF luffing mechanism,firstly,we develop a hierarchical method to deduce the Jacobian matrix and Hessian matrix for obtaining the kinematics equations.Subsequently,we divide the luffing mechanism into six bodies considering actuators,and deduce the kinetic equations of each body by the Newton-Euler method.Based on the dynamic model,we simulate the luffing process.Finally,a prototype is built on a pile driver to validate the model.Simulations and experiments show that the dynamic model can reflect the dynamic properties of the proposed luffing mechanism.And the control strategy that the front cylinders retract first shows better mechanical behavior than the other two control strategies.This research provides a reference for the design and application of 2-DOF luffing mechanism on construction machinery.The modeling approach can also be applied to similar mechanism with serial closed kinematic chains,which allows to calculate the dynamic parameters easily and exactly.
基金the National Natural Science Foundation of China(Nos.51902178,11804188,51702172,and 51802285)the Natural Science Foundation of Shandong Province(No.ZR201807060932)the Open Fund of the State Key Laboratory of Luminescent Materials and Devices(South China University of Technology)(No.2019-skllmd-15)。
文摘To introduce ordered nano-structures inside a transparent amorphous matrix with superior optical and mechanical properties bears scientific and technological importance,yet limited success has been achieved.Here,via simple melting-quenching and subsequent thermal activation,we report the successful preparation of transparent nano-structured glass-ceramics embedded in Sr2Lu F7 nano-crystals(~26 nm),as evidenced by X-ray diffraction,transmission electron microscopy(TEM),and high resolution TEM.The successful incorporation of dopants into formed Sr2Lu F7 nano-crystals with low phonon energy results in highly tunable blue–green photoemission,which depends on excitation wavelength,dopant type,and temperature.We found that Eu3+and Eu2+ions co-exist in this hybrid optical material,accompanied by the broadband blue emission of Eu2+and sharp red emissions of Eu3+.A series of optical characterizations are summoned,including emission/excitation spectrum and decay curve measurement,to reveal the reduction mechanism of Eu3+to Eu2+.Furthermore,near green–white photoemission is achieved via the enrichment of Tb3+/Eu3+into crystallized Sr2Lu F7 nano-crystals.The temperature-dependent visible photoemission reveals thermal activation energy increases with the precipitation of Sr2Lu F7 nano-crystals in a glass matrix,suggesting better thermal stability of glass-ceramics than precursor glasses.These results could not only deepen the understanding of glass-ceramics but also indicate the promising potential of Eu3+/Tb3+-ions-doped Sr2Lu F7 glass-ceramics for UV pumped white light emitting diodes(WLEDs)with good thermal stability.
