Positioning behavior resulting from the application of ultrasonic oscillation to a linear motion ball bearing during step motion

In general, positioning accuracy of precision machineries equipped with a moving table is strongly influenced by friction encountered by linear motion rolling bearings. However, ultrasonic oscillation is often applied to bearing surfaces to reduce the friction. This report describes the behaviors in the process of step positioning of a one-axis linear motion stage guided by a linear motion ball bearing. In experiment, the transient step positioning response of a voice-coil-motor-driven stage is observed using a linear encoder. Moreover, a guide rail and a carriage of the guideway are oscillated by two ultrasonic actuators. As a result, continuous oscillation throughout the process of positioning causes the settling time for the stopping position to deteriorate because there is less friction of contact surfaces in bearing. On the other hand, a 10 ms oscillation after the start of the movement and a 75 ms oscillation around the settlement simultaneously improve the average displacement of positioning from 1.0097 mm to 1.0030 mm and shorten the delay time of movement from 14.975 ms to 14.65 ms.