3107 Study on Positioning Accuracy and Thermal Behavior of Nut/Shaft Air Cooling Ball Screw for High-precision Feed Drive

Ball screw is a precision mechanical linear actuator that uses steel balls between a screw shaft and a nut to transfer the motion which convert rotary into linear movement when screw is rotated. Different from any conventional power transmission screw, which needs to overcome sliding friction between the screw and the nut threads, ball screw operates similar to bearing components could achieve high mechanical efficiency since it moves in relatively low rolling friction. As a tried and tested technology, ball screw drive systems are still used in a majority of machine tools which can meet the demands of higher productivity and tight part tolerances due to their low cost and high degree of stiffness. High speed ball screw drive system generates more heat and it results in greater positioning error, adversely affecting the accuracy of high precision machined parts. In consideration of the complicated unpredictable working condition of the ball screw drive system, a well designed nut/screw air cooling ball screw system was developed and be applied to a mass produced ball screw used in a high precision CNC machine tool which can avoid thermal error that affect the positioning accuracy and the temperature rise of in all working conditions. In order to discuss the effectiveness of the developed high speed/high precision nut/screw air cooling ball screw system, a series of tests was carried out in several kind of working condition. As results, the thermal deformation improved 58.7%〜80.1% by nut cooling, screw cooling and nut/screw cooling at the 2500 s moment. Similar with the thermal deformation case, relatively big temperature rising presented through the whole test process in no cooling condition and "Learning curve" phenomenon presented in the cooling cases. The dominated temperature rising area covered the nut moving range completely. Even the cooling methods can control the heat that distribute on the screw surface very well, the cooling performance in the bearing parts is uncertain. Despite excellent positioning accuracy and cooling performance of the ball screw introduced in this research, the average noise elevates 6.25% in the nut cooling, 14.1% in the screw cooling and 15.3% in the nut/screw cooling comparing with the no cooling case.