Jiro Otsuka

Characteristic Comparison of 3 Kinds of Leadscrews Used for Ultraprecision Positioning.

The characteristic comparison of three kinds of leadscrews (a precision sliding screw, a precision ball screw and a rolled ball screw) is described on the one-dimensional ultraprecision positioning apparatus with a position feedback system in the PTP method. The followings are clarified ; (1) Since the damping factor of the ball screw is ten times smaller than that of the sliding screw, the table response using the ball screw is sharper and shows a larger vibration, (2) when three kinds of leadscrews have the same friction torque at low speed, the relationship between the variation of the friction torque and the positioning error is clarified from the quantified point of view by a step response using the proportional control. (3) The relationship between the electric current of the DC servomotor and the table displacement in the step response under sub-micronmeter stroke is of stick-slipping characteristic for the sliding screw and of elastic characteristic for the ball screw.

A fundamental study of simulation for leadscrew wear. Proposition of cylindrical model and basic experiment.

A method is discussed in which the wear process in the leadscrew-nut system is simulated using a couple of cylindrical models proposed. To simplify the contact condition geometrically between screw and nut with trapezoidal thread profile, a couple of cylindrical models touching each other in the end surfaces is applied. The wear of the practical leadscrew is simulated by observing the wear depth at the end surface of the cylindrical model corresponding to the wear depth at the flank of thread. In order to evaluate the propriety of the cylindrical model, the wear tests of the practical leadscrews and the simulation tests with the cylindrical models are performed. In the simulation tests, the testing conditions, such as the materials of specimens, the type of lubricant, the contact area ratio, the contact pressure and the sliding speed, are similar to those in the practical tests. It is considered on the basis of the experimental results that the lubricating condition and the wear character along the frictional surfaces of the simulator are corresponding to those of the practical system, and a prospect is obtained that the simulation for the leadscrew wear is possible by the cylindrical model within the limits of the condition set in this study.