Abstract
It is of great significance to study the dynamic characteristics of twin ball screw (TBS) feed system to improve the precision of gantry-type dual-driven computer numerical control (CNC) machine tools. In this paper, an equivalent dynamic model of the TBS feed system is established utilizing lumped mass method considering the stiffness of joints. Equivalent axial stiffness of screw-nut joints and bearing joints are both calculated by Hertz contact theory. Furthermore, a friction model is proposed because the friction force of the screw nut affects the stiffness of the joints. Then, the friction parameters are obtained by using the nonlinear system identification method. Meanwhile, a finite element model (FEM) is developed to assess the dynamic characteristics of TBS feed system under the stiffness of joints. Finally, validation experiments are conducted, and the results show that the positions of the nut and the velocities of worktable greatly affect the dynamic characteristics of the TBS feed system. Compared with the theoretical calculation, FEM and experiments indicate that the dynamic modeling proposed in this article can reach a higher accuracy.
Highlights
Twin ball screw (TBS) redundant feed system has been widely used in precision computer numerical control (CNC) equipment with high accuracy, high rigidity and high stability
Used the lumped mass method to establish dynamic model of high speed feed system considering the joint stiffness, calculated the joint stiffness by using Hertz contact theory, and discussed the effect of different factors consisting of axial force, friction force and preload on stiffness of the transmission chain, but these conclusions were not extended to the twin ball screw (TBS) system
This article considers the stiffness of the typical joints of the TBS feed system, takes the self-developed TBS two-dimension worktable as the research object, and establishes the equivalent transmission stiffness model of the TBS worktable
Summary
Twin ball screw (TBS) redundant feed system has been widely used in precision computer numerical control (CNC) equipment with high accuracy, high rigidity and high stability. Used the lumped mass method to establish dynamic model of high speed feed system considering the joint stiffness, calculated the joint stiffness by using Hertz contact theory, and discussed the effect of different factors consisting of axial force, friction force and preload on stiffness of the transmission chain, but these conclusions were not extended to the TBS system. Modal test based on experiments can be further divided into experimental modal analysis (EMA) and operational modal analysis (OMA) All these researches above have made great contributions to the understanding of the dynamic characteristics of a ball screw feed system. This paper reveals that joint stiffness and friction force of screw-nut have great effects on dynamic characteristics of the TBS feed system. The results show that the proposed model agrees significantly moreso with the experimental results than the discrete model and hybrid model do
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