Experimental Study of Friction Losses in Ball Screws

Abstract

In contrast with conventional sliding lead screws, ball screws with rolling friction between the screw and nut have high efficiency, accurate positioning and smooth, quiet operation at low friction that make this kind of systems ideal for use in a wide variety of equipments (precision measuring, transportation, office automation, medical) in many industries such as machine-tools building, robots, fine mechanics, automotive, truck and tractors, aircraft, nuclear reactor, printing, paperprocessing, automatic, textile, cutting and grinding machines. The safety of mechanical systems that use ball screws depends on friction phenomena on the ball and tracks contact surfaces which can significantly reduce the positioning accuracy. An experimental equipment was designed and tested in order to measure friction losses in a ball screw transmission. The mechanical device has two hydrostatic pretensioned ball nuts which ensure a highly accurate transmission of motions with an increased rigidity, especially for accurate positioning. Experimental tests were carried out on a 32 mm diameter worn-out ball screw in dry friction conditions, at low speed and thrust loads.