Workspace analysis of a 6-degree-of-freedom hybrid robot with two parallel modules

Abstract Workspace analysis is a crucial step in designing any robotic system and ensuring its safe operation. This article analyzes the workspace of a six degree-of-freedom (6-DOF) hybrid robot, which includes two separate modules with parallel architectures placed above each other. The upper module is a 4-DOF Delta-type parallel mechanism, and the lower module is a 2-DOF rotary mechanism with a circular rail. With this design, the hybrid robot represents a relative manipulation system, and workspace analysis is performed in the relative motion of the modules. This approach differs from other similar studies that combine the workspaces determined for each module independently, and we propose a method and derive results more suitable for practical use. To solve the workspace analysis problem, the paper develops a discretization-based approach, which considers all mechanical constraints. These constraints include joint constraints of each module and link interference between the modules. To analyze this interference, we apply the Gilbert–Johnson–Keerthi algorithm and represent the links as convex polytopes. Multiple numerical examples illustrate the developed techniques and show the translation and orientation workspaces of the robot for various relative configurations of its modules. Computer-aided-design simulations validate the proposed theoretical algorithms. The results demonstrate that the link interference between the modules, often ignored in other works, limits the workspace and should be considered for the proper workspace evaluation and design of similar hybrid robots.