Theoretical And Experimental Analysis On The Transmission Efficiency Of The Double-nut Ball Screw

Transmission efficiency of the ball screw is an important factor to assess its transmission performance,which is related to a variety of parameters and performance of ball screw.At present,the transmission efficiency value adopted by the manufacturer is only associated to the lead angle and the friction coefficient,where the influence of the actual working conditions is ignored.The present transmission efficiency curve is only applicable to the single nut ball screw,but the calculation method for the double nut ball screw is lack.Due to the complexity of the structure and the diversity of the stress,the transmission efficiency of the double-nut ball screw changes under different working conditions,and the load on the left and right nuts varies with the axial load,which determines the force and torque exerted by the left and right nuts on the screw,resulting in the change of transmission efficiency.Considering the variation of force,the friction coefficient,as a conversion factor between force and friction force,affects the transmission efficiency directly.Under different rotational speeds,the lubrication state of the ball screw will change,and the corresponding friction coefficient will change as well.Therefore,this paper takes the transmission efficiency as the core and studies the transmission efficiency of the double-nut ball screw from the aspects of load,speed,and friction coefficient as the key parameters.The specific research contents are as follows:(1)The load distribution model of the ball screw is established.Unlike the previous view that the balls undertake the stress evenly,in consideration of the lead screw bearing way,axial load,torque,rigid contact rigidity and screw,nut,based on factors such as the establishment of a double nut ball screw load distribution model,and further analyzes the different types of double nut ball screw under the condition of different load and different speed around inside the nut-ball contact force,contact deformation,the fluctuation situation,for the double nut ball screw transmission efficiency calculation model laid the foundation.(2)The Stribeck curve of the friction coefficient of the ball screw is described.The friction coefficient of the ball screw varies under the influence of load and rotation speed.In the traditional calculation process,the friction coefficient is generally determined according to the empirical value or empirical formula.Under the conditions of different loads and rotating speeds,the friction coefficient is usually set.In this paper,the Stribeck curve of friction coefficient of ball screw was constructed by simultaneously measuring the friction moment and axial load of ball screw and calculating the friction coefficient under different load and rotational speed conditions.Stribeck lubrication parameter was used as the horizontal coordinate.Based on the Coulomb friction,not only friction but also Stribeck friction,a basic equation for describing the friction coefficient of the ball screw was established.The results of the experiment and calculation show that the lubrication state of ball screw under different load and rotation speed mainly includes three types: mixed lubrication,hydrodynamic lubrication,and stable lubrication.Under different lubrication conditions,the friction coefficient of the ball screw presents different changes.(3)Based on the basic law of thermodynamics,the temperature change of the ball screw within the whole running distance is calculated.Based the thermal deformation in the ball screw,the influence of the temperature change on the preload is obtained,and finally the transmission efficiency changes with the temperature change.(4)The calculation model of transmission efficiency of ball screw with double nuts is established.Considering the different working conditions of the ball screw,the influence of various loads on the transmission efficiency of the ball screw was analyzed,and the overall calculation model of the transmission efficiency was constructed.Through the load distribution model and friction coefficient change model built above,the torque generated by each part of the load is solved,to realize the calculation of the transmission efficiency of the double nut ball screw Considering the different deformation of the forward and backward running state of the ball screw,the transmission efficiency of the forward and reverse running is analyzed,and the practical application conditions of the double nut ball screw aiming at the optimization of the transmission efficiency are put forward.(5)A test device for transmission efficiency detection of the ball screw is established.To verify the correctness of the proposed calculation model,a transmission efficiency testing device is constructed.The test device is driven by a torque motor and loaded by a linear motor.The actual transmission efficiency of the double-nut ball screw can be obtained by testing the load and speed of the nut end face and the input torque and speed of the screw shaft.