Abstract
The distinguishing feature of a vertical ball screw feed system without counterweight is that the spindle system weight directly acts on the kinematic joints. Research into the dynamic characteristics under acceleration and deceleration is an important step in improving the structural performance of vertical milling machines. The magnitude and direction of the inertial force change significantly when the spindle system accelerates and decelerates. Therefore, the kinematic joint contact stiffness changes under the action of the inertial force and the spindle system weight. Thus, the system transmission stiffness also varies and affects the dynamics. In this study, a variable-coefficient lumped parameter dynamic model that considers the changes in the spindle system weight and the magnitude and direction of the inertial force is established for a ball screw feed system without counterweight. In addition, a calculation method for the system stiffness is provided. Experiments on a vertical ball screw feed system under acceleration and deceleration with different accelerations are also performed to verify the proposed dynamic model. Finally, the influence of the spindle system position, the rated dynamic load of the screw-nut joint, and the screw tension force on the natural frequency of the vertical ball screw feed system under acceleration and deceleration are studied. The results show that the vertical ball screw feed system has obviously different variable dynamics under acceleration and deceleration. The influence of the rated dynamic load and the spindle system position on the natural frequency under acceleration and deceleration is much greater than that of the screw tension force.
Highlights
The ball screw is widely used in the X, Y, and Z axes of high-speed and high-precision machine tools; its importance is self-evident
Mao et al [22] proposed a method for the modal decoupling of operational deflection shapes to investigate the dynamic behavior of machine tools with respect to different worktable feed rates, and pointed out that changing the worktable feed rate affects the contribution of different vibration modes to the machine tool vibration
The analytical model presented in this study can accurately reflect the dynamic characteristics of the vertical ball screw feed system
Summary
The ball screw is widely used in the X, Y, and Z axes of high-speed and high-precision machine tools; its importance is self-evident. Structural dynamics simulations, and stability assessments were simultaneously carried out On this basis, Zou et al [28] discussed the influence of the screw-nut joint stiffness on the position-dependent dynamics of a vertical ball screw feed system without counterweight and found that the spindle system counterweight should be considered when estimating the dynamics of a vertical ball screw feed system without counterweight. In this study, the dynamics of a vertical ball screw feed system without counterweight under acceleration and deceleration are investigated considering the spindle system weight. 2.1 Equivalent Dynamic Model To study the variation in the dynamic characteristics of a vertical ball screw feed system under upward acceleration and deceleration, the structure of the system, as shown, is first described.
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