Vibration Modelling and the Difference Between Different Vibration Models for a Fewer-DOF Parallel Robot

The accuracy of the vibration model used in the design process directly affects the vibration performance of a parallel robot in practice, which determines the machining accuracy and the surface finish of the manufactured products. Considering a drilling parallel robot with a passive branch and few degrees of freedom as the implementation object, a vibration modelling method is proposed in which Kane’s equation is utilized, and various commonly ignored factors, such as the passive branch, the joint clearances and gravity, are considered. To explore the effects of the passive branch, which was considered ideal in previous studies, two dynamic models are derived in which the passive branch is rigid or flexible. To explore the effects of the joint clearances, which were ignored in previous studies, two stiffness models of branches are derived, in which the joint clearances are considered or ignored. Finally, numerical examples are presented for analysing the effects of these commonly ignored factors on the vibration performance of the drilling parallel robot. Regarding to the effects of these commonly ignored factors, the findings of this paper can serve as a reference for designers in simplifying the vibration model in the design process of parallel robot.

General Dynamic Model of Flexible Multi-Body Systems With Its Application in Gun Systems

General purpose software for kinematic and dynamic simulation of flexible multi-body systems is serviced widely to practical engineering fields. In this paper general dynamic model of flexible multi-body systems with its application in gun systems is set up vie Kane’s equation. The “0-1” method is presented for calculating partial velocities, partial angular velocities and coefficients matrix of the differential equations of motion. Techniques of automatic modeling for dynamic analysis of flexible multi-body systems of gun systems are introduced in this paper, which include automatic identification of systems configuration, automatic determination of degrees of freedom, automatic derivation of kinematic formulas, automatic application of load, automatic generation and solution of motion equations and so on. Because of automatic modeling, overelaborate procedures are avoided, and model on general purpose is realized, which can be conveniently used in dynamic simulation for launching process of gun systems and validly applied to design of them. Finally, a numerical example is given to demonstrate the feasibility of general algorithms proposed.