Ball-splined shaft assembly

Abstract

A ball-splined shaft assembly suitable for use in a robot arm or the like is provided. The assembly includes a shaft formed with a plurality of circumferential grooves spaced apart from one another at a predetermined pitch and a pair of longitudinal grooves which are located opposite sides and extend in parallel with the center line of the shaft. An outer sleeve unit fitted onto the shaft includes a pair of endless circulating paths each provided with a plurality of balls. Each of the endless circulating paths includes a load path section where the balls are partly exposed and thus received in the corresponding one of the longitudinal grooves. The outer sleeve unit is mounted on a housing through a pair of ball bearings. Thus, the shaft may rotate together with the outer sleeve unit relative to the housing and the shaft may move in its longitudinal direction relative to the outer sleeve unit and thus the housing. A stepping motor is mounted on the housing and operatively coupled to the outer sleeve unit. A linear step motor structure is formed in the housing and located in a side-by-side relation with the outer sleeve unit so that the shaft may be driven to move in its longitudinal direction by the linear step motor structure.