Type synthesis of parallel mechanism with 3T/3R motion patterns

As the competitor of 6-degree-of-freedom parallel mechanisms (PMs) in multi-tasks, parallel mechanisms with multi-motion patterns (PMMPs) have aroused considerable interest from re-searchers. This article investigates the type synthesis of parallel mechanisms with both three translational (3T) and three rotational (3R) motion patterns based on switch manner design. Having addressed the fundamentals of finite and instantaneous screws with regard to motion computations and differential mapping, the relationship between motion patterns is analyzed in the view of algebraic transformation operations. Then switch manners are discussed including both finite motion-driven and instantaneous singular motion-driven methods. An integrated expression is formulated to describe the whole moving process by defining transformation items. In this way, the type synthesis is carried out through four steps: switch manner design, integrated motion description, limb generation, and assembly condition solving. Numerous parallel mech-anisms with 3T/3R motions are obtained and a typical application for space robots is presented. In this approach, different motion patterns are connected algebraically, and switch manners driven by both singular motion and finite motion are unified, which realize a unified and direct type synthesis process.