Kinematics,Load Distribution And Elastohydrodynamic Lubrication Of Ball Screw Mechanism

Ball screw mechanism is a type of high-precision transmission component that is frequently used in CNC machines.Its operating principle is to convert the sliding friction of the screw and nut into rolling friction via the use of balls,making it perform with high transmission efficiency,good synchronization performance,and the ease of achieving high precision and sensitivity transmission.As CNC machine tools continue to expand in efficiency,precision,and size,the demand for ball screws’ speed and load capacity continues to rise.However,the ball screw mechanism is prone to wear and heat up under high speed and heavy load conditions,resulting in a loss of accuracy and dependability,as well as a serious failure.The wear and heat issues associated with high speed and heavy load situations have severely hampered the ball screw mechanism’s future application in this field.As a result,it is critical to perform in-depth research on the ball screw mechanism’s wear and heat mechanisms.The ball screw mechanism’s kinematic properties,load distribution,and elastohydrodynamic lubrication state all have a significant effect on its wear and heating.This article begins with the three aspects of motion,load,and lubrication and improves them considering the shortcomings and limitations of the existing theory,as well as thoroughly discussing the influence of the ball screw mechanism’s working parameters and structural parameters on its motion,load,and lubrication state.The following summarizes the major research conducted:(1)Kinematics theory is used to construct and analyze the kinematic properties of a ball screw.The velocity of the ball,screw,and nut are determined,as well as the relative linear velocity of each surface at the contact point.A new method for evaluating and measuring the ball screw mechanism’s slide-to-roll ratio and entrainment velocity using the Frenet frame as a reference is proposed.The results indicate that the ball screw slips at the contact point,but the degree of slip is extremely modest,and the slide-to-roll ratio and entrainment speed at the screw and nut contact points are extremely close.(2)We build an analytical model of the ball screw mechanism’s load distribution taking lead inaccuracy into account.To begin,the lead error is modeled,followed by a discussion of the effect of each parameter in the linear error and periodic error on the load distribution.The results indicate that a linear lead error alters the load ratio between the front and rear rows of balls,thereby subjecting the raceways at the nut’s ends to greater contact loads;the effect of a periodic lead error on the maximum contact load increases linearly with the error’s amplitude,but the effect of a special frequency error on the load distribution is negligible.(3)The effect of the return mechanism on load distribution was compared for several types of ball screw mechanisms.We modeled the four most common ball chain models:complete ball chain,internal returns,end cap tangential returns,and external returns.The number and location of balls were determined,and the four models’ load distributions were compared further.Due to the gap in the ball chain,the results demonstrate that the uneven load distribution of external returns is more obvious than in other types.(4)The lubrication status of a ball screw is analyzed using the results of kinematics and load distribution studies,as well as the fundamental theory of starved elastohydrodynamic lubrication.The thickness of the oil film at various locations within the nut affected by load distribution is compared,and the effect of various ball screw structural parameters on the minimum film thickness is investigated.Finally,the effect of lubrication settings on the film thickness is investigated further,providing a theoretical foundation for ball screw lubrication enhancement.