| A ball screw driven mechanism is a key component of numerical control machine tools. With the development of high-speed cutting technology, the feed rate of the ball screw becomes faster and faster. However, with the development of ball screws tends towards high-speed, problems such as noise, high temperature resulted from fiction become more and more badly. Therefore the problem of the noise and friction becomes the key factor to increase the ball screw speed. Therefore, it is significant to study the dynamical performance of ball screw mechanism and research the pivotal influencing factors on the performance. The study provides effective guidance to increase the dynamic performance of high-speed ball screw mechanism.The problems of friction torque and noise in high-speed of ball screw mechanism are studied by applying contact mechanics, impact mechanics, the theory of elastohydrodynamic lubrication (EHL) and structural noise, and combining the friction torque and noise test. The contents of this paper are as follows.1) Considering helical angle, the contact characteristic between balls and grooves is studied based on the theory of Hertz. And the influences of structural parameters on the contact characteristic are investigated.2) Based on kinematics theory, the kinematic relation between balls and screw shaft is analyzed and the influences of important structural parameters on spinning and slip of balls are investigated.3) The mechanical model of impact between the ball and the returner is proposed based on the theory of Hertz contact and the Newton Second Law. A special device is designed to measure the time of impact-contact process. The influences of impact angle, structural parameters and material of ball screw mechanism on the impact force are investigated. Furthermore, the motion of the balls on the groove after impact and the fluency of the balls in returner groove are investigated.4) According to the design features of ball screw mechanism, a model of friction torque is proposed to analyze the composition and generation of friction torque. The influence of manufacturing errors of grooves on friction torque is analyzed. And the lubrication state of the ball screw mechanism is investigated by applying the theory of elastohydrodynamic lubrication. Combining the test result and spectrum of friction torque, the reason of the fluctuation of friction torque of ball screw mechanism is investigated.5) The noise characteristic of end-cap type ball screw mechanism is compared with return pipe type ball screw mechanism through spectrum analysis of noise. The relation between noise and vibration of end-cap type ball screw in high speed is investigated and the noise generating mechanism of this type ball screw is ascertained.The conclusions of theoretical analysis and experimental study results are as follows:1) The contact stress and deformation between balls and screw shaft groove are larger than the side between balls and nut groove. The contact stress and deformation decrease with increasing of the contact angle. And the variation of helical angle has no noticeable influence on contact characteristic of ball screw mechanism. However, the contact characteristic is very sensitive to the variation of the curvature ratio. The contact stress and deformation increases remarkably as the curvature ratio increases.2) At normal rotational speed, although the motion speed of ball center is not high, the rotational speed is quite high. The size of a ball has no noticeable influence on the spin-to-roll ratio of a ball, but the contact angle is of remarkable influence on the spin-to-roll ratio. When the contact angle is equal to 38°, the spin-to-roll ratio reaches the minimum point. The slippage ratio of a ball is increased with the increase of helical angle and the size of a ball.3) The test result proves that the model of impact behavior between ball and returner based on Hertz contact model and the Newton Second Law is reliable. The impact force increases greatly with the increase of impact angle and the incipient speed of the ball. The impact force can be decreased through using smaller steel balls or ceramic balls, decreasing impact angle, or making returner with engineering plastic whose elastic modulus is smaller than the steel. The small elastic modulus, small restitution coefficient and good friction characteristic material is the best selection to make returner.4) The manufacturing errors of groove in ball screw mechanism affect the value of the friction torque averagely. The errors increase the total value of the friction torque. For the ball screw contact couple, it is difficult to built full elastohydrodynamic lubricating film. Usually, the parameter A of lubrication state is smaller than one, and the contact couple runs on conditions of boundary lubrication. Therefore the high friction coefficient resulted from poor lubrication may be the primary reason of the high friction torque.5) When the ball screw mechanism runs at lower speed and is lubricated by oil, the friction torque of ball screw is higher than at high speed. And the friction torque of the inner-return type and bayonet-tube type ball screw mechanism often fluctuates at the normal frequency of 1Hz. When the ball screw mechanism is lubricated by grease, the friction torque is smaller and changes smoothly. Analysis indicates that the fluctuation of the friction torque at the normal frequency of 1Hz is resulted from the jam and fall off of balls because of poor lubrication.6) The sound volume of the end-cap type ball screw mechanism is much smaller the bayonet-tube type, what's more the tone quality of the end-cap type is much better than the bayonet-tube type. The principal frequency of the noise varies with the rotational speed of the ball screw mechanism. The vibration of the table jointed with nut has nothing to do with the noise of ball screw mechanism. The noise of end-cap type ball screw mechanism is caused by the forced vibration of the nut which is inspired by the waviness of screw shaft groove, the noise caused by the impact between the ball and the returner is not the principle noise. When the ball screw mechanism is lubricated with grease, the spectral distribution remains the same, but the sound volume declinesslowly.
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