Development of Half-floating Leadscrew and its application

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Sliding leadscrews have superior advantages of higher stiffness and vibration dumping effects than ball screws or hydrostatic leadscrews though they have disadvantage of large friction loss. This study proposes a method of improving the frictional property without deteriorating the advantage of stiffness and vibration dumping effects. Pneumaticpressure is supplied to contact interfacebetween threads to support the axial load partially, while the solid contact areas aremaintained tokeep stiffness and dumping effect. This study aims at developing the "half-floating leadscrew", to verify its availability and clarify the problems.First, to obtain data for designing the half-floating leadscrew, some experiments are performed using cylindrical model. The contact condition of screw threads is modeled to contacts between end surfaces of cylinders, and their frictional property is clarified to understand the friction decrease by the pneumatic pressure. The.frictional torque between the cylinders is measured under various conditions of axial load, pneumatic pressure and rotational speed. From the experimental results, it is confirmed that the cylindrical model shows 38 % decrease of friction loss when increasing pneumatic pressure by 0.1 MPa under the axial load of F=147 N.Next, a half-floating leadscrew is manufactured by approving simple pneumatic slots to a sliding leadscrew. The nominal screw threads profile is metric trapezoidal thread of Tr30 X 8. The recess of 2.4 mm width and 0.6mm depth is formed on the female threads. Thematerial of the nut is bronze casting ( BC6 ), while the material of the screw shaft is SCM415H. It is confirmed that the friction loss is decreased by 40 % when the pneumatic pressure is P=0.3 MPa under the axial load of F=147 N. And so, the availability of the half-floating leadscrewproposed is verified. Moreover, a positioning mechanism is constructed in order to apply the manufactured half-floating leadscrew.