Abstract
Modern tendency of machine tools design requires more accurate model to predict the system dynamics, in order to anticipate its interaction with machining process. In this paper, a comprehensive dynamic model of ball screw feed system (BSFS) considering nonlinear kinematic joints is introduced to investigate the varying dynamic characteristics when worktable is subjected to combined load from six directions. The load–deformation relationship of each kinematic joint is dealt with a set of translational and angular spring elements. The nonlinear restoring force function of each joint involving coupling displacement is calculated. Based on the lumped mass method, the analytical 18-DOF dynamic equation is formulated by the analysis of the interaction force between joints. Model verification tests are conducted. The worktable response exhibits the abundant and fascinating nonlinear phenomena arising in nonlinear joint and coupling effect. The nonlinear behavior behaves significant difference owing to the variations of excitation, platform position, screw length, preload and damping of joints. Thus, the model is promising for comprehension of machine dynamic behavior and for development of sophisticated control strategy.
Highlights
With the ever-increasing development of modern manufacturing industry, demands for more precise and high-speed CNC (Computer Numerical Control) machine tools have been put forward
The ball screw feed system (BSFS) accompanied with rolling linear guideway platform is the popular unit to realize linear motion of CNC machine tools owing to good kinematic accuracy, smooth motions, low wear and long service lifetime without a stick-slip effect [8]
The approximately 60% of the total dynamic stiffness and approximately 90% of the total damping of the entire machine tool structure originates in the kinematic joints [9,10], and the complication and instability of vibration may be dramatically affected by the nonlinearity of joints among supported bearing, nut and carriage [11,12,13,5,14]
Summary
With the ever-increasing development of modern manufacturing industry, demands for more precise and high-speed CNC (Computer Numerical Control) machine tools have been put forward. An accurate dynamic model of feed drive system is essential for the prediction of structural vibration and the enhancement of operating behavior of CNC machine tools. Considering the nonlinear stiffness of rolling guide joints owing to the point contact between ball and raceway, Wang et al [24] developed a dynamic model of three-axis coupling machine tool to evaluate the axis coupling effect as well as position-dependent response of tool center point. Wang et al [13] derived the coupling relevance of linear guideways, screw-nut, screw shaft and supported bearings and studied the mechanical behavior of nonlinear kinematic joints for ball screw driven CNC axis, the yawing vibration behavior of worktable failed to be estimated and only the axial vibration response of screw-nut, shaft and bearings was highlighted. The proposed model can be used to identify the mechanism of time domain vibration response, understand the posture variation, and develop precise numerical model algorithms to determine the vibration characteristics of BSFS
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