Study Of Ball Screw Mechanism And Friction Heat

Ball screws are special linear actuators,which transform energy into a translation movement that provides a useful work.They are commonly used in many fields of application.For example,commercial airplanes have ball screws in mechanisms such as engine thrust reversers,ABS automotive brakes have ball screws that open valves that release fluid pressure to brake pads.Industrial applications include machine tools,milling-machine tables,and robotics.Each time an application needs a translation movement,ball screws are an excellent choice among others like pneumatic,hydraulic cylinders,lead screws,and roller screws.An electric motor,usually a DC motor is connected to the screw.Therefore,a control system can be made including the electric motor control.Based on characteristic mechanical relationships of the ball screw,special displacement sensors,speed sensors,torque sensors,the control system can be a closed-loop system.Indeed,precision is a crucial matter for most applications.Precision errors have many sources: friction forces,thermal deformation,load and preload elastic deformation,balanced mounting problems,vibrations.This present study will mainly focus on friction effect and heat effect caused by friction.Friction has a negative effect for linear actuators like ball screws.It mainly happens between the balls and the screw on the one hand,and between the balls and the nut on the other hand.Generating heat,the friction deforms the components of the system like balls and screw,and thus increases the imprecision of the displacement.Compared to simple nut-screw mechanisms,ball screws have a far better efficiency thanks to their rolling elements.However,for high precision applications,understanding friction phenomenon and heat generation is important in order to further compensate these problems.Heat simulation along the screw and experimental test on the precision of the position of the nut will lead us to compare the results and to evaluate the importance of heat generation in the lack of precision.