| A ball screw driven mechanism is a key component of numerical control machine tools.With the continuous development of CNC machine tools to the direction of the high-speed, high precision, the linear velocity of the ball screw is also increasing. Which Makes the ball screw wear and tear, temperature rise and noise increases.In this thesis, on the basis of analysis of contact and motion characteristics of ball screw,the generation mechanism of the friction torque and vibration characteristics of ball screw units are studied.Which has important theoretical significance and practical value to solve the problem of the temperature rise due to high speed and noise.First, features of ball movement in spiral raceway are analyzed on the basis of contact mechanics,movements of the two contact points on the raceway between the ball screw and nut are resolved.The couple along the direction of movement of the ball center and the equations in all directiongs are analyzed. Ball slip as the unique movement patterns of ball screw assembly is also obtained,and then the generation mechanism of the friction torque of ball screws and the main factors are elaborated.Mathematical model of a ball screw friction torque and the formula of the ball screw heat are also built by the generation mechanism of the friction torque.The model of the ball screw drive system is Simplified on basis of vibration and noise theory,and then the natural vibration of the model after simplified is then solved.Variation of the ball screw friction torque with different reverse devices and different lubrication methods has been researched by experiments.The causes of low-frequency fluctuations of friction torque have also been researched.Which shows that the main causes are balls’ periodic entering & exiting the reverse device and periodic congestion and spread caused by Ball screw manufacturing error.Temperature changes over time of the KD3216 ball screw with new reverse device has been measured at different rotation speeds.The experiment shows a temperature rise in less than 20℃after stable in the speed of 60m/min.Which depicts a nice smooth performance,can significantly reduce the friction among the balls.Modal experiment and simulation on the ball screw comprehensive capability bench have been done. Main natural frequencies have been obtained.the relationship between main noise energy in different bands and different speed of the spindle has also been obtained. |
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