| As an important component of the transmission screw of the automatic control system of aerospace equipment,marine engineering equipment and the feed mechanism of CNC equipment such as high-grade CNC machine tools,the dynamic characteristics of the ball screw are closely related to the performance of the whole equipment.The reciprocating motion of the ball screw nut will affect the rigidity and dynamic characteristics of the screw.At the same time,with the increasing speed of the screw,the high speed also has a certain impact on the dynamic characteristics of the bearing supporting the screw.Therefore,the analysis of the dynamic characteristics of highspeed ball screw bearing coupling system is great significance for the structural design,optimization and high-speed and accurate operation of the ball screw.Aiming at the dynamic characteristics and operational stability of the high-speed ball screw pair-bearing coupling system,this paper adopts the Timoshenko beam theory and the concentrated mass method by considering the changes in the center of mass of the screw nut and the influence of the supporting bearing.The dynamic characteristics of the auxiliary-bearing coupling system were studied.The natural frequency and critical speed of the high-speed ball screw-bearing system are analyzed.Finally,the unbalanced response of the high-speed ball screw pair-bearing coupling system is verified by experiments,which provides a theoretical basis for improving the stability of the high-speed ball screw pair-bearing coupling system.The main research contents are as follows:(1)The dynamic stiffness analysis model of the high-speed ball screw is established.The dynamic stiffness analysis model of the high-speed ball screw is established under the condition that the centroid position of the screw nut changes at any time.The feasibility of the dynamic stiffness analysis model is verified by calculating the natural frequencies of the ball screw.It provides a basic theory for the dynamic design and structure optimization of the high-speed ball screw.(2)Calculation of natural frequency and critical speed of the high-speed ball screw bearing coupling system.Based on the dynamic stiffness analysis model with the change of screw nut centroid position,the finite element model of the high-speed ball screw bearing coupling system is established considering the influence of bearing.The influences of screw nut position,bearing stiffness,bearing preload,gyroscopic moment and screw inner diameter on the natural frequency and critical speed of the coupling system are analyzed.The results show that: when the nut runs to the middle of the effective stroke of the screw,the running stability of the ball screw pair will have a small fluctuation;when the stiffness and preload of the bearing are increased,the higher natural frequency and critical speed of the coupling system can be obtained;when the gyroscopic moment is properly increased,the critical speed of the coupling system can be improved.(3)Unbalance response analysis and experimental verification of the high-speed ball screw bearing coupling system.According to Newmark-β method,the vibration response of unbalanced mass to bearing at both ends and the vibration response of different eccentric mass to the instant of lead screw emergency stop and start are analyzed.The principle,equipment and experimental data of the experiment are introduced to verify the unbalance response of the high-speed ball screw bearing coupling system.The results show that: the unbalanced mass on the lead screw has a greater response to the vibration of the bearing far away from the motor end;under the same eccentric mass,the vibration response at the maximum stroke position of the lead screw far away from the motor end is more sensitive at the moment when the lead screw nut stops and starts abruptly. |
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