Configuration Synthesis of Fully-Symmetrical Parallel Positioning Mechanism for In Situ Machining of Large Structural Components

The surface of large structural components is composed of materials with different hardness and complex shapes, and it presents significant challenges in achieving precise and efficient positioning as well as high-precision grinding. In-situ processing machine overcomes the limitations of grinding machines such as poor adaptability to different materials and limited travel, and becomes a promising solution for efficient processing of large complex structural components. In-situ processing machine is composed of car, positioning and different processing devices. The positioning mechanism with full-symmetrical layout in parallel topology can effectively guarantee the positioning accuracy and machining stiffness, and is the best scheme for in-situ machining mechanism. Aiming to provide a novel topology structure for subsequent mechanism development. This paper carries out theoretical research on the composition of its topological structure. As an efficient configuration synthesis theory combining numerical and geometrical aspects, finite and instantaneous screw (FIS) theory is applied in this paper. Firstly, the required motions for the grinding operation are characterized based on finite screw, representing the desired motion of the mechanism. Then, single-degree-of-freedom factors are added afterwards to obtain the standard type of the limb structure. Secondly, the factors in the standard type are equivalent transformations and displacements based on the properties of screw triangle product to obtain the derivative and expanded types of limb structure. The feasibility is verified through the synthesis algorithm or transformation properties of finite screw. Finally, taking three feasible limb structures as examples, three fully-symmetrical parallel positioning mechanisms are configured based on assembly conditions and actual requirements. This paper presents a configuration synthesis process for the fully-symmetrical parallel positioning mechanism, obtaining various new topology structures and laying a theoretical foundation for subsequent research.