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RISS 인기검색어
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- 저자 : Enlai Zheng (검색결과 4 건)
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Enlai Zheng,Yuanzhao Yang,Zhaohui Peng,Yue Zhu,Xiao Zhao,Xiangze Lin,Min Kang 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.6
Thermal models are important in the process of predicting the thermal characteristics and corresponding thermal error of multi-link high-speed precision presses (MLHSPPs) with an oil-lubrication system. Previous models only involved the effects of bearing stiffness, temperature change of bearings, flexibility of crank shaft on the heat generation power, while the influences of revolute clearance joint and flexibility of linkage are seldom considered, which inevitably reduces the accuracy of thermal analysis. To overcome this problem, dynamic models of flexible multi-link mechanisms (MLM) with clearance, lubrication, crankshaft-bearing system are constructed, the interaction forces between pin and bushing are obtained to calculate its heat generation power. Then, an improved model of MLHSPP with lubrication is proposed to analyze the temperature evolution and the thermal error between slider and work table at the position of LDP, by considering bearing stiffness, temperature change of bearings, flexibility of crank shaft, linkage, clearance, lubrication and thermal contact resistance all together. Compared with results from traditional models, the simulation data from this improved thermal model agree well with experiment, which proves the validity of the proposed model. Furthermore, the temperature rise and the thermal error of MLHSPP between slider and work table at the position of LDP under different input speeds, lubricating oil flux and contact angles of ball bearing were also studied.
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Enlai Zheng,Xinlong Zhou,Sihong Zhu 대한기계학회 2014 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.28 No.7
It is essential to establish a dynamic model to predict and evaluate the dynamic performance of a nonlinear dry friction mounting systemduring design procedure, when it is impossible to carry out the test of prototype. Unlike the conventional ideal dry friction modelwhere the direction of dry friction force is always considered to be opposite to that of relative velocity, a new equivalent resistance modelof dry friction force is proposed based on the bilinear hysteretic model by introducing a parameterg in this work. The equivalent resistancecontains spring force and damping force, whose direction is not opposite to that of relative velocity. Then, a dynamic model of theblock foundation with nonlinear dry friction mounting system is established. When the equivalent resistance is applied to the dynamicmodel, its dynamic responses are obtained under common practical forms of press loads: rectangular pulse, half-sine pulse, and triangularpulse. Compared to experimental results, the dynamic responses based on the equivalent resistance model are more consistent with thesimulation results based on the ideal dry friction model and the validity of the equivalent resistance model for the bilinear hystereticmodel in this work is verified. Furthermore, the effect of the pulse shape and pulse duration on the dynamic responses of the block foundationwith nonlinear dry friction mounting system is investigated.
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An improved thermal model for characteristics analysis of multi-link ultra-precision press system
Enlai Zheng,Shilu Xie,Jin Zhang,Yue Zhu,Xiao Zhao,Xiangze Lin,Min Kang 대한기계학회 2018 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.32 No.1
In traditional models, only the effect of temperature change of bearings on the heat generation power and thermal contact resistance is considered. But the effect of bearing stiffness and flexibility of crank shaft on the heat generation power is often neglected, thereby impairing the accuracy of the thermal analysis. Therefore, a better thermal model is demanded to accurately analyse the thermal characteristics of a Multi-link ultra-precision press system (MLUPPS). By combining the effect of stiffness of bearing and flexibility of crank shaft on the heat generation power, an improved thermal model of MLUPPS was developed in this work. The model was based on as-derived kinematic and dynamic equations of Multi-link transmission mechanism (MLTM) and flexible dynamic model of crankshaft-bearing system. The dimension chain of thermal error is constructed to analyse the dimensional error between the slider and the work table at the position of Bottom dead point (BDP). The developed thermal model of MLUPPS and its analysis results from this model are in good agreement with the measurement results, and that is more accurate than the traditional one. The simulation results reveal that the maximum temperature rise of MLUPPS occurs at the crank shaft, and the dimensional error between the slider and the work table at the position of BDP is due to thermal expansion fluctuation before the generation and conduction of heat power reaches balance. The temperature rise and thermal error of MLUPPS under different rotation speeds, piling forces and bearing stiffness were also studied.
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Enlai Zheng,Yindong Fan,Rui Zhu,Yue Zhu,Jieyu Xian 대한기계학회 2016 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.30 No.9
It’s essential to establish a dynamic model of a wheeled tractor with suspended driver seat including air spring and Magnetorheological (MR) damper to analyze its vibration characteristics and performance. The equivalent linearized model of the wheeled tractor always neglects the effect of nonlinear stiffness for scissors linkage driver seat and air spring with auxiliary chamber as well as dynamic characteristics of real tractor tyre and considers the driver seat as linear spring and damper elements, which causes the analysis to have a lower precision. We considered the effect of nonlinear stiffness for scissors linkage seat and air spring with auxiliary chamber as well as MR damper and dynamic characteristics of real tyre and developed a complete nonlinear dynamic model of wheeled tractor with suspended driver seat including air spring and MR damper. The experimental results demonstrate that the improved nonlinear dynamic model is more consistent with the actual state than the equivalent linearized model, and the validity of the proposed model is verified. Furthermore, the effect of forward speed, ratio of volume for air spring with respect to volume of auxiliary chamber, and area of orifice on the acceleration of wheeled tractor was also investigated, which can provide a theoretical basis for control algorithm design of semiactive vibration isolation system.
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