3D3A class of parallel mechanisms: Design and performance evaluation

Abstract

This paper presents a study of 20 six-degrees-of-freedom (DoF) Generalized Stewart–Gough Platform (GSP) type mechanisms in 3D3A class. These mechanisms are characterized by three distance and three angular constraints between their base platforms (BPs) and moving platforms (MPs). The mechanisms are categorized into two groups based on the geometric shapes of their BPs and MPs. The platform shapes are determined by the types of joints and their connection configurations on the platforms. The platforms are designed with regular polygonal shapes. Two groups are generated according to whether the geometric shapes of the platforms are the same or different. There are 10 types of mechanisms in the first group, where the BP and the MP shapes of each are the same. The second group also includes 10 types of mechanisms, each with two design variations, resulting in 20 designs. Thus, a total of 30 mechanisms are designed. The reachable workspaces and dexterities of these manipulators are computed to assess the impact of design parameters such as the ratio between the BP and MP radii and the rotation of one end of the BP edges. The reachable workspace volume and the Global Conditioning Index (GCI) are selected as the performance metrics. The results of all mechanisms are presented in the paper, with a comparison of the two best mechanisms against the classical 3×3 Stewart Platform. The study shows that the $D_4^3{A}_1^3$ type mechanism achieves a large reachable workspace while maintaining a high GCI value.