The Issue of Type Synthesis of Kinematic Chains of Spherical Parallel Mechanisms with Linear Drives

The issue of structural synthesis of kinematic chains of spherical parallel mechanisms with linear drives is considered. Screw calculus is used to analyze the mobility of chains. Possible structures of chains, including three and four passive rotary kinematic pairs, are successively investigated. It is shown that, if there are three rotary pairs in the chain, the synthesis of a spherical mechanism with linear drives is impossible, and the use of chains with four rotary pairs for this purpose is possible if there is a planar dyad in the chain, including a driving prismatic pair and two rotary pairs.