Dynamics Model of 4-SPS/CU Parallel Mechanism With Spherical Clearance Joint and Flexible Moving Platform

2017 ◽  
Vol 140 (2) ◽  
Author(s):  
Gengxiang Wang ◽  
Hongzhao Liu
Keyword(s):  
Parallel Mechanism ◽  
Dynamic Performance ◽  
Friction Model ◽  
Contact Forces ◽  
Flexible Body ◽  
Force Model ◽  
Spherical Joint ◽  
Dynamics Model ◽  
Clearance Joint ◽  
Moving Platform

Effects of flexible body and clearance spherical joint on the dynamic performance of 4-SPS/CU parallel mechanism are analyzed. The flexible moving platform is treated as thin plate based on absolute nodal coordinate formulation (ANCF). In order to formulate the parallel mechanism's constraint equations between the flexible body and the rigid body, the tangent frame is introduced to define the joint coordinate. One of the spherical joints between moving platform and kinematic chains is introduced into clearance. The normal and tangential contact forces are calculated based on Flores contact force model and modified Coulomb friction model. The dynamics model of parallel mechanism with clearance spherical joint and flexible moving platform is formulated based on equation of motion. Simulations show that the dynamic performance of parallel mechanism is not sensitive to the flexible body because of the inherent property of moving platform; however, when the clearance spherical joint is considered into the parallel mechanism with flexible body, the flexible moving platform exhibits cushioning effect to absorb the energy caused by clearance joint.

Three-Dimensional Wear Prediction of Four-Degrees-of-Freedom Parallel Mechanism With Clearance Spherical Joint and Flexible Moving Platform

2018 ◽  
Vol 140 (3) ◽  
Author(s):  
Gengxiang Wang ◽  
Hongzhao Liu
Keyword(s):  
Contact Force ◽  
Parallel Mechanism ◽  
Degrees Of Freedom ◽  
Three Dimensional ◽  
Contact Forces ◽  
Force Model ◽  
Spherical Joint ◽  
Normal Contact ◽  
Tangential Contact ◽  
Moving Platform

Three-dimensional (3D) wear of the clearance spherical joint in four-degrees-of-freedom (DOF) parallel mechanism is predicted based on Archard's wear model. The flexible moving platform is treated as thin plate element based on absolute nodal coordinate formulation (ANCF). The tangent frame is introduced to formulate the constraint equation of universal joint. One of the spherical joints is treated as clearance joint. The normal and tangential contact forces are calculated based on Flores contact force model and modified Coulomb friction model. In order to predict 3D wear, the normal contact force, tangential contact velocity, and eccentricity vector are decomposed in the global coordinate system. Simulation results show that 3D wear occurred in three directions are not uniform each other.

Dynamic Response and Nonlinear Characteristics of Spatial Parallel Mechanism With Spherical Clearance Joint

2019 ◽  
Vol 14 (4) ◽  
Author(s):  
Chen Xiulong ◽  
Li Yuewen ◽  
Jia Yonghao
Keyword(s):  
Dynamic Response ◽  
Contact Force ◽  
Dynamic Equation ◽  
Parallel Mechanism ◽  
Joint Clearance ◽  
Spherical Joint ◽  
Nonlinear Characteristics ◽  
Clearance Joint ◽  
Spatial Parallel Mechanism ◽  
Moving Platform

Spherical joint is a type of common kinematic pair in spatial parallel mechanism. The existence of spherical joint clearance has many adverse effects on the mechanism. A method of forecasting the dynamic behaviors of spatial parallel mechanism with spherical clearance joint is proposed. The 4-UPS-UPU spatial parallel mechanism with spherical clearance is taken as the research object, the dynamic response, and nonlinear characteristics of the mechanism are studied. The kinematic model and the contact force model of the spherical clearance are established. The dynamic equation of the spatial parallel mechanism with spherical joint clearance is derived by Newton–Euler method. The above-mentioned dynamic equation is solved by using the ODE113 function that is based on a variable order numerical differential algorithm in matlab. The dynamic responses of moving platform with different clearance values are analyzed. The contact force and the center trajectory of the sphere at the spherical joint are obtained. In addition, the phase trajectory, Poincare map, and bifurcation diagram are analyzed, and the nonlinear characteristics of the spherical clearance joint and the moving platform are obtained. By comparing the results, such as the acceleration of moving platform and the contact force, with virtual prototype simulation, the correctness of the dynamic equation of the spatial parallel mechanism with spherical clearance joint and the analysis results are verified. The researches show that the change of clearance value has a great influence on the motion state of spherical clearance joint, and chaos phenomena appears in the clearance joint with the increase in the clearance value. And the impact phenomenon appears between the spherical joint elements, which makes the mechanism generated vibration.

Dynamic Analysis and Wear Prediction of Planar Five-Bar Mechanism Considering Multiflexible Links and Multiclearance Joints

2017 ◽  
Vol 139 (5) ◽  
Author(s):  
Gengxiang Wang ◽  
Hongzhao Liu
Keyword(s):  
Contact Force ◽  
Dynamic Performance ◽  
Contact Forces ◽  
Force Model ◽  
Displacement Curve ◽  
Wear Depth ◽  
Wear Model ◽  
Clearance Joint ◽  
Contact Force Model ◽  
Cylindrical Joint

Effects of wear and member flexibility on the dynamic performance of a planar five-bar mechanism with joint-clearance are investigated. The equation of motion of the mechanism is derived based on the absolute nodal coordinate formulation (ANCF). In order to enhance the accuracy of the contact force, the slope of the load–displacement curve of the cylindrical joint with clearance is used. The contact deformation couples the joint wear to the contact state. The contact force model of Flores and coworkers is improved, by the introduction of the stiffness coefficient. The wear depth is predicted by using the Archard's wear model. Simulations show that the multiclearance joints can generate stronger contact forces relative to single clearance joint case. This leads to more severe wear in the joint. However, the mechanism with multiple flexible links can absorb more of the energy arising from the clearance joint, and this improves the wear phenomenon.

scholarly journals A new impact dynamics model of a clearance joint considering the adhesive effects in space environment

2020 ◽  
Vol 306 ◽  
pp. 01005
Author(s):  
Ruiting Tong ◽  
Zefen Quan ◽  
Qi Wan ◽  
Xiaojun Fu ◽  
Geng Liu
Keyword(s):  
Hybrid Model ◽  
Contact Process ◽  
Contact Forces ◽  
Space Environment ◽  
Impact Dynamics ◽  
Force Model ◽  
Dynamics Model ◽  
Clearance Joint ◽  
The Impact ◽  
Adhesive Forces

In space environment, there is severe adhesive effect, and the impact contact process shows different phenomenon due to the adhesive forces. In this paper, a new impact dynamics model of a clearance joint is developed considering the adhesive effects. The Hertz contact model, L-J potential and Dugdale model are combined, and an adhesive force term is included in the original hybrid contact force model. Taking a clearance joint as an example, the theory of adhesive forces during the impact contact process is given, and the influence of the adhesive forces is investigated. Negative forces are discovered at the beginning of the contact, and the contact forces of the modified model are higher than the hybrid model. Besides, the indentation depth is also higher than the hybrid model. The energy conservation principle is employed to explain the phenomena, and the contact forces will be underestimated if the adhesive effects are ignored. This work could be contributed to estimating the contact forces and friction forces more reasonablely in the space environment.

Elastodynamics modeling of 4-SPS/CU parallel mechanism with flexible moving platform based on absolute nodal coordinate formulation

2017 ◽  
Vol 232 (21) ◽  
pp. 3843-3858 ◽  
Author(s):  
Gengxiang Wang
Keyword(s):  
Coordinate System ◽  
Parallel Mechanism ◽  
Absolute Nodal Coordinate Formulation ◽  
Dynamic Performance ◽  
Flexible Body ◽  
Surface Approach ◽  
Absolute Nodal Coordinate ◽  
Cylindrical Joint ◽  
Moving Platform ◽  
Joint Coordinate System

The moving platform of the 4-SPS/CU (S is the spherical joint, P is the prismatic joint, C is the cylindrical joint, U is the universal joint) parallel mechanism is treated as a thin-plate element based on the absolute nodal coordinate formulation due to its physical characteristic. In order to eliminate high-frequency modes caused by the coupling between membrane and bending effects, the elastic mid-surface approach is used to evaluate the elastic force of the flexible moving platform. In order to formulate constraint equations between the flexible body and the rigid body, the tangent frame is introduced to define the joint coordinate system that is rigidly attached to the node at the joint, which is convenient for determining the constant vector in the joint coordinate system. The dynamics model of the parallel mechanism with the flexible moving platform is built based on the equation of motion. The simulation results show that the vibration frequency caused by the flexible body will be increased with the increasing stiffness of the material, and the kinematic trajectory and dynamics performance of the parallel mechanism are affected seriously when the smaller Young’s modulus is used, which illustrates that the effect of the flexible moving platform on the dynamic performance of the parallel mechanism should not be ignored.

Dynamics Analysis of Truss Deployment Mechanism With Imperfect Joint Considering Input Fluctuation

2020 ◽  
Author(s):  
Zhengfeng Bai ◽  
Jijun Zhao ◽  
Xin Shi
Keyword(s):  
Contact Force ◽  
Dynamic Performance ◽  
Mathematic Model ◽  
Friction Model ◽  
Dynamic Responses ◽  
Force Model ◽  
Normal Contact ◽  
Clearance Joint ◽  
Contact Force Model ◽  
Dynamic Performance Analysis

Abstract Modern spacecraft usually has large deployment structure, which consisting of plenty of joints could produce undesirable dynamic responses when considering clearances in joints and driving input fluctuation. However, in the dynamic performance analysis of space deployment mechanism, the clearances and input fluctuation are always ignored. In this study, the dynamic responses of a flexible planar scissor-like truss deployment mechanism with imperfect joint considering clearance and input fluctuation are investigated using computational methodology. First, the mathematic model of clearance joint is established. The revolute clearance joint is considered as force constraint and the joint components of an imperfect joint with clearance are modeled as contact bodies. The normal contact force model of clearance joint is established using a continuous contact force model considering energy loss. The friction effect is considered using a modified Coulomb friction model. Then, the dynamics performances of the flexible planar scissor-like truss deployment mechanism with imperfect joint considering clearance and input fluctuation are presented and discussed. Different case studies for the scissor-like truss deployment mechanism with clearance are investigated considering driving input fluctuation. The simulation results show that the dynamic characteristics of the mechanism with clearance joint are changed more obviously when considering driving input fluctuation. Therefore, investigation implies that dynamics responses of the truss deployment mechanism are much worse when considering clearance joint and input fluctuation, which indicates that driving input fluctuation leads to more obvious degradation of the dynamic performance of the truss deployment mechanism with imperfect joint.

Wear Analysis of Spatial Parallel Mechanisms With Multiple Three-Dimensional Spherical Clearance Joints

2019 ◽  
Vol 141 (10) ◽  
Author(s):  
Chen Xiulong ◽  
Jia Yonghao
Keyword(s):  
Parallel Mechanism ◽  
Surface Profile ◽  
Friction Model ◽  
Dynamic Responses ◽  
Force Model ◽  
Parallel Mechanisms ◽  
Clearance Joints ◽  
Wear Analysis ◽  
Clearance Joint ◽  
Analysis Of Dynamics

The goal of this work is to investigate the dynamic responses of the parallel mechanism with irregular clearances caused by wear and to further reveal the influences of multiple clearance interaction on wear. The motion model and the force model of spherical clearance joint based on a continuous contact force model and a static friction model are established. The dynamic equation of the spatial parallel mechanism considering two spherical clearance joints is derived. A general wear analysis strategy to establish spherical clearance joint with sustainable updation of the surface profile is presented, and the dynamic responses of parallel mechanism after wear are studied. The interaction between two wear joints with different initial clearance values is further investigated. The results show that it is necessary to consider the factor of irregular clearances caused by wear in the analysis of dynamics behavior for precision mechanisms. Proper distribution of clearance values can reduce wear of clearance joint and improve the useful life of mechanism to a certain extent. This work provides a foundation for life prediction and reliability analysis of parallel mechanisms.

scholarly journals Dynamics of Multibody Systems With Spherical Clearance Joints

2005 ◽  
Author(s):  
P. Flores ◽  
J. Ambro´sio ◽  
J. C. P. Claro ◽  
H. M. Lankarani
Keyword(s):  
Contact Force ◽  
Multibody Systems ◽  
Contact Forces ◽  
Force Model ◽  
Clearance Joints ◽  
Continuous Contact ◽  
Clearance Joint ◽  
Contact Force Model ◽  
Dynamics Of Multibody Systems ◽  
The Impact

This work deals with a methodology to assess the influence of the spherical clearance joints in spatial multibody systems. The methodology is based on the Cartesian coordinates, being the dynamics of the joint elements modeled as impacting bodies and controlled by contact forces. The impacts and contacts are described by a continuous contact force model that accounts for geometric and mechanical characteristics of the contacting surfaces. The contact force is evaluated as function of the elastic pseudo-penetration between the impacting bodies, coupled with a nonlinear viscous-elastic factor representing the energy dissipation during the impact process. A spatial four bar mechanism is used as an illustrative example and some numerical results are presented, being the efficiency of the developed methodology discussed in the process of their presentation. The results obtained show that the inclusion of clearance joints in the modelization of spatial multibody systems significantly influences the prediction of components’ position and drastically increases the peaks in acceleration and reaction moments at the joints. Moreover, the system’s response clearly tends to be nonperiodic when a clearance joint is included in the simulation.

scholarly journals Dynamic response analysis for multi-degrees-of-freedom parallel mechanisms with various types of three-dimensional clearance joints

2021 ◽  
Vol 18 (3) ◽  
pp. 172988142110177
Author(s):  
Jia Yonghao ◽  
Chen Xiulong
Keyword(s):  
Dynamic Response ◽  
Multibody Systems ◽  
Parallel Mechanism ◽  
Three Dimensional ◽  
Response Analysis ◽  
Parallel Mechanisms ◽  
Dynamics Model ◽  
Clearance Joints ◽  
Clearance Joint ◽  
Spatial Parallel Mechanism

For spatial multibody systems, the dynamic equations of multibody systems with compound clearance joints have a high level of nonlinearity. The coupling between different types of clearance joints may lead to abundant dynamic behavior. At present, the dynamic response analysis of the spatial parallel mechanism considering the three-dimensional (3D) compound clearance joint has not been reported. This work proposes a modeling method to investigate the influence of the 3D compound clearance joint on the dynamics characteristics of the spatial parallel mechanism. For this purpose, 3D kinematic models of spherical clearance joint and revolute joint with radial and axial clearances are derived. Contact force is described as normal contact and tangential friction and later introduced into the nonlinear dynamics model, which is established by the Lagrange multiplier technique and Jacobian of constraint matrix. The influences of compound clearance joint and initial misalignment of bearing axes on the system are analyzed. Furthermore, validation of dynamics model is evaluated by ADAMS and Newton–Euler method. This work provides an essential theoretical basis for studying the influences of 3D clearance joints on dynamic responses and nonlinear behavior of parallel mechanisms.

Effects of Mechanical Flexibility and Clearance Size on the Wear at Revolute Joint in the Flexible Multibody Systems

2014 ◽  
Author(s):  
Bo Zhao ◽  
Xudong Dai ◽  
Shihao Wu
Keyword(s):  
Contact Force ◽  
Numerical Approach ◽  
Friction Model ◽  
Force Model ◽  
Wear Prediction ◽  
Normal Contact ◽  
Continuous Contact ◽  
Clearance Joint ◽  
Flexible Multibody ◽  
Flexible Component

By integrating the procedures of wear prediction with multibody dynamics, this paper proposed a numerical approach for the modeling and prediction of wear at revolute clearance joint in flexible multibody mechanical systems. In the approach, the flexible component was modeled by using absolute nodal coordinate formulation (ANCF)-based element. The clearance joint was modeled as a dry contact pair, in which the continuous contact force model proposed by Lankanrani and Nikravesh was applied to evaluate the normal contact force, and the friction effect was considered using the LuGre friction model. The calculation of wear was performed by an iterative wear prediction procedure based on Archard’s wear model. Using this approach, a planar slider-crank mechanism including a flexible rod and clearance joint was numerically investigated as a demonstrative example. Furthermore, the effects of the flexibility of the mechanism and the clearance size on the wear at clearance joint were also studied.

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