Coupling Mechanism of Errors in the Planetary Roller Screw Mechanism

Abstract

In order to reveal the error coupling mechanism of thread pair and gear pair in the planetary roller screw mechanism (PRSM), a transmission error calculation model considering the error of gear and thread was established. This paper analyzed the thread pair error firstly, including assembly errors, eccentricity errors and errors caused by load. Secondly, the errors of gear pair including profile deviation, helix deviation and pitch deviation were analyzed, then the matrix of tooth surface flexibility coefficient was obtained by finite element method, and the transmission errors of the gear were further obtained. Thirdly, according to the structural characteristics of transforming rotating motion into linear motion and the same speed of roller gear and roller thread in the PRSM, the circumferential errors of gear were converted into axial error of nut. Thus, the coupling relation between gear pair and thread pair was established. Finally, the final transmission error curve was obtained. The final transfer error was a sine-like curve and the amplitude equaled to 0.02957 mm, which increased by 11.59% compared to the unconsidered gear errors, and the fluctuation was greater.