Theoretical Study of the Load Distribution on the Threads for Roller Screw Mechanisms of a Friction Type

Abstract

The paper provides theoretical research of load distribution across the thread turns of the planetary roller-screw mechanism (RSM). A characteristic feature of the theoretical approach of the paper is the use of a RSM rod model with two elastic contact layers (the first layer is composed of screw-rollers, the second – of nut-rollers). A threaded mating of each elastic layer is considered as a connection with continuous turns, which is closest to the truth and consistent to classical approaches. A similar approach was applied for the ball-and-screw mechanisms with a member point contact. Thus, differential analytical closed-form equations may be used to solve this task.Based on the initial equation of compatibility of strains, axial offsets of contact layer points and the sum of screw, roller and nut turn deflections are calculated; then, load distribution across the turns may be determined. Load distribution depends both on the RSM geometry (pitch, profile angle, entry number, and thread diameter), material of threaded elements, manufacturing accuracy, and on mating friction forces. With the dependencies of load distribution across the turns of zero-clearance RSMs obtained, we have determined that maximum load is imposed on the outermost turns, which corresponds to classical solutions proposed by N. E. Zhukovski.