Dynamic Modeling and Analysis of 4UPS-UPU Spatial Parallel Mechanism with Spherical Clearance Joint

Clearance between the moving joints is unavoidable in real working process. At present, many researches are mainly focused on dynamics of plane revolute joint in plane mechanism, but few on dynamics of spatial spherical joint clearance in spatial parallel mechanism. In this paper, a general method is proposed for establishing dynamic equations of spatial parallel mechanism with spatial spherical clearance by Lagrange multiplier method. The kinematic model and contact force model of the spherical joint clearance were established successively. Lagrange multiplier method was used to deduce the dynamics equation of 4 UPS-UPU mechanism with spherical clearance joint systematically. The influence of friction coefficient on dynamics response of 4 UPS-UPU mechanism with spherical clearance joint was analyzed. Non-linear characteristics of clearance joint and moving platform were analyzed by Poincare map, phase diagram, and bifurcation diagram. The results show that variation of friction coefficient and clearance value had little effect on stability of the mechanism, but the chaotic phenomenon was found at spherical clearance joint. The research has theoretical guiding significance for improving the dynamic performance and avoiding of chaos of parallel mechanisms including spherical joint clearance.

Dynamics Response and Non⁃linear Characteristics Analysis of Complex Planar 2⁃DOF Mechanism with Revolute Clearances

There are clearances in mechanism because of manufacture and assembly error,which reduces operation life and working accuracy of mechanism and has a great impact on dynamical responses.At the moment,research in this area mainly focuses on single degree⁃of⁃freedom mechanism considering one clearance,while research of multi⁃DOF mechanism considering multi⁃clearance is less.With the purpose of studying the dynamical characteristics of complex multi⁃DOF mechanism with multi⁃clearances,a dynamic model was developed.The dynamic responses of 2⁃DOF mechanism with two clearances under different positions,values,and numbers of clearance were analyzed.The displacement,velocity,acceleration,collision force,and the axis trajectory at clearance were then given.In addition,there is a limited amount of literature on chaotic phenomena,which mainly focuses on the chaotic phenomena of end⁃effector of mechanism.But in this paper,the non⁃linear characteristics were analyzed by chaotic phenomenon of clearance joint,then chaotic phenomenon was identified by Poincarémappings and phase diagrams.Bifurcation diagrams were given.The results will offer a reliable technical support for the study of dynamical responses of planar mechanisms and the analysis of chaotic phenomena.

Reflection on the Construction of Tropical and South Subtropical Agricultural Experimental Station CATAS( Jiangmen)

This paper introduces the origin and progress of Tropical and South Subtropical Agricultural Comprehensive Experimental Station( hereinafter referred to as experimental station) CATAS( Jiangmen),formulates the thought for construction of experimental station,analyzes the restrictive factors and puts forward corresponding countermeasures in order to provide reference for the decision- making and implementation of constructing the experimental station.

Experimental and numerical investigations of the compressive behavior of carbon fiber-reinforced polymer-strengthened tubular steel T-joints

A method for strengthening damaged tubular steel T-joints under axial compression by wrapping them with carbon fiber-reinforced polymer(CFRP)sheets was proposed and evaluated.The influence of the CFRP strengthening on the failure mode and load capacity of T-joints with different degrees of damage was investigated using experiments and finite element analyses.Five T-joints were physically tested:one bare joint to obtain the peak load and corresponding displacement(D1m),two reinforced joints to provide a reference,and two pre-damaged then retrofitted joints to serve as the primary research objects.The ratio of the pre-loaded specimen chord displacement to the value of D1m was considered to be the degree of damage of the two retrofitted joints,and was set to 0.80 and 1.20.The results demonstrate that the maximum capacity of the retrofitted specimen was increased by 0.83%–15.06%over the corresponding unreinforced specimens.However,the capacity of the retrofitted specimen was 2.51%–22.77%lesser compared with that of the directly reinforced specimens.Next,111 numerical analysis models(0.63≤b≤0.76,9.70≤g≤16.92)were established to parametrically evaluate the effects of different geometric and strengthening parameters on the load capacity of strengthened tubular T-joints under different degrees of damage.The numerical analysis results revealed that the development of equivalent plastic strain at the selected measuring points was moderated by strengthening with CFRP wrapping,and indicated the optimal CFRP strengthening thickness and wrapping orientation according to tubular T-joint parameters.Finally,reasonable equations for calculating the load capacity of CFRP-strengthened joints were proposed and demonstrated to provide accurate results.The findings of this study can be used to inform improved CFRP strengthening of damaged tubular steel structures.