Averaging Effect on Pitch Errors in Hydrostatic Lead Screws With Continuous Helical Recesses

The motion errors of hydrostatic lead screws can be smaller than the pitch errors due to the averaging effect of oil films, which is the so-called averaging effect on the pitch errors (AEPE). This paper investigates the factors influencing AEPE under low speeds and a constant external load. An equivalent model of hydrostatic lead screws with continuous helical recesses is established, and the axial motion errors of the nut are obtained by combining the dichotomy and finite difference methods. The results show that (a) the motion errors caused by the pitch errors of the lead screw have additivity, and the pitch errors of the nut have little influence on the motion errors, (b) when the lead screw only has cumulative pitch errors, the motion errors are equal to the average value of the cumulative pitch errors located on the two flank surfaces of the lead screw, and (c) when the lead screw only has periodic pitch errors, the number of nut threads with helical recesses n and the period of the pitch errors of the lead screw T are the main influencing factors on AEPE.