Xiulong Chen

Kinetoelastodynamics Modeling and Analysis of Spatial Parallel Mechanism

The nonlinear elastodynamic modeling and analysis of the 4-UPS-UPU spatial 5-degree-of-freedom parallel mechanism are investigated. The kinetoelastodynamics theory is used to derive the elastic dynamic equations of 4-UPS-UPU spatial parallel mechanism. In order to grasp the effect of geometric nonlinearity on dynamic behaviors, such as displacement error output, velocity error output, acceleration error output, stress of driving limbs, and natural frequencies, the variations of dynamic behaviors considering geometric nonlinearity and without considering geometric nonlinearity are discussed, respectively. The numerical simulation results show the nonlinear elastodynamic model established can reasonably reflect the dynamic behaviors of 4-UPS-UPU spatial parallel mechanism with flexible driving limbs. And geometric nonlinearity is demonstrated to have significant impact on dynamic response and dynamic characteristics of spatial parallel mechanism. The researches can provide important theoretical base for the optimal design of spatial parallel mechanism.

Nonlinear Elastodynamic Behaviour Analysis of High-Speed Spatial Parallel Coordinate Measuring Machines

In order to study the elastodynamic behaviour of 4- universal joints- prismatic pairs- spherical joints / universal joints- prismatic pairs- universal joints 4-UPS-UPU high-speed spatial PCMMs(parallel coordinate measuring machines), the nonlinear time-varying dynamics model, which comprehensively considers geometric nonlinearity and the rigid-flexible coupling effect, is derived by using Lagrange equations and finite element methods. Based on the Newmark method, the kinematics output response of 4-UPS-UPU PCMMs is illustrated through numerical simulation. The results of the simulation show that the flexibility of the links is demonstrated to have a significant impact on the system dynamics response. This research can provide the important theoretical base of the optimization design and vibration control for 4-UPS-UPU PCMMs.

Dexterity Analysis of a 4-UPS-RPS Parallel Mechanism

A novel 4-UPS-RPS spatial 5 degrees of freedom parallel mechanism is introduced and its dexterity measures are analysed. The stationary platform of the parallel mechanism is connected with the moving platform by the same four UPS (universal joints-prismatic pairs-spherical joints) driving links and a RPS (revolute joints-prismatic pairs-spherical joints) link. The velocity Jacobian matrix and the force Jacobian matrix of the parallel mechanism are derived, and the dimensionless velocity Jacobian matrix is established. On this basis, the three dexterity measures, including average conditional number, the smallest singular value and operation, are obtained. According to these, the square mean dexterity coefficient, which is used to comprehensively evaluate the dexterity of various configurations, is proposed. In addition, the distribution of different dexterity measures above in the workspace is analysed respectively. This research can provide an important theoretical base for the dimensional synthesis and trajectory planning for a parallel mechanism.

Rigid Dynamic Model and Analysis of 5-DOF Parallel Mechanism

This paper introduces a novel 4-UPS-RPS spatial parallel mechanism, which can achieve three rotation degrees and two translation degrees of freedom. A rigid dynamic model is established and analysis of the parallel mechanism is carried out. The kinematics of the RPS and UPS driving limbs are analysed and the velocity-mapping relationships between the driving limbs and the other parts are built. The load conditions of the parts are analysed, and the rigid dynamic model of the 4-UPS-RPS parallel mechanism is derived by the virtual work principle approach. Using the example of the parallel mechanism movement, a driving forces analysis of the 4-UPS-RPS parallel mechanism is carried out, and the correctness of the rigid dynamic model is verified by numerical calculation and virtual simulation.

Nonlinear Dynamics and Analysis of a Planar Multilink Complex Mechanism with Clearance

In order to understand the nonlinear dynamic behavior of a planar mechanism with clearance, the nonlinear dynamic model of the 2-DOF nine-bar mechanism with a revolute clearance is proposed; the dynamic response, phase diagrams, Poincare portraits, and largest Lyapunov exponents (LLEs) of mechanism are investigated. The nonlinear dynamic model of 2-DOF nine-bar mechanism containing a revolute clearance is established by using the Lagrange equation. Dynamic response of the slider’s kinematics characteristic, contact force, driving torque, shaft center trajectory, and the penetration depth for 2-DOF nine-bar mechanism are all analyzed. Chaos phenomenon existed in the mechanism has been identified by using the phase diagrams, the Poincare portraits, and LLEs. The effects of the different clearance sizes, different friction coefficients, and different driving speeds on dynamic behavior are studied. Bifurcation diagrams with changing clearance value, friction coefficient, and driving speed are drawn. The research could provide important technical support and theoretical basis for the further study of the nonlinear dynamics of planar mechanism.

Kinematics Analysis of a Parallel Coordinate Measuring Machine

A 4-UPS-UPU 5-Degrees of Freedom PCMM(Parallel coordinate measuring machine), which can achieve three translation degrees of freedom and two rotational degrees of freedom, is presented in this paper. The inverse position model of the 4-UPS-UPU PCMM is established. The Jacobian matrix, and the expressions of velocity and acceleration are deduced. Furthermore, a numerical analysis of the inverse solutions of the position, velocity and acceleration are carried out. The results are confirmed by a virtual simulation of the 4-UPS-UPU PCMM prototype. This research has laid a solid foundation for the motion control and movement performance analysis of the 4-UPS-UPU PCMM.