Study On Lubrication And Friction Of Engagement Pair Of Precision Ball Drive

The precision steel ball transmission is a new precise small tooth difference planetary transmission by using the steel ball cycloid groove engagement pairs to reduce and using the steel ball ring groove engagement pairs to equi-speed outputting. This precision transmission will be widly used in the future for it’s outstanding advantages of no revese error,large overlap drgree and meshing efficiency.The construction constituted and the drive principles and the motion state of the engagement pairs of the precision steel ball transmission is analyzed. According to the mechanical properties of the engagement pairs, the difference of the engagement pairs acting force is calculated in the linear and nonlinear conditions is analyzed. The motion characteristics of the precision steel ball transmission is studied and the sliding speed formulas of the cycloid groove engagement pairs and the ring groove engagement pairs isdeduced.On the basis of contact mechanics and kinematics studies of the precision steel ball transmission, minimum film thickness formula of precision ball transmission meshing vice is derived by applying Hamrock-Dowson formula. The influence rule of the cycloid groove engagement pairs minimum film thickness of the basic parameters such as curtate ratio and rolling radius and steel ball radius are studied by applying numerical calculation method in the MATLAB.The lubrication condition of engagement pair is analysed and discriminated, the calculation method of the parameter selection of engagement pair in a state of complete elastohydrodynamic lubrication is proposed, the range of the basic parameters is also calculated. The influence rule of the ring groove engagement pairs minimum film thickness of the basic parameters such as the number of the ring groove and steel ball radius is studied.The resistance torque causing reason of the the precision steel ball transmission is analyzed. According to the calculation methods of friction torque of the ball bearing and ball screw, the calculation formula of the cycloid groove and the ring groove engagement pairs, analysis model of the precision steel ball transmission resistance torque is established.On the base of this, the method of the decrease of the transmission resistance torque is proposed and theory basis for design and application for the precision steel ball transmission is provided.