Conceptual Reconfigurable Design and Kinematic Analysis of the Exechon-Like Parallel Kinematic Machine

Reconfigurable and modular designs can be a key technology to realize the versatility as well as improve the flexibility of parallel kinematic machines(PKMs). Inspired by the design of the high-performance Exechon PKM, two novel Exechon-like PKMs-Exe-Ⅰ and Exe-Ⅱ are proposed on the basis of the Exe-Variant PKM. Four types of reconfigurable Exechon-like PKM modules-Exechon, Exe-Variant, Exe-Ⅰ, and Exe-Ⅱ were conceptually designed by following the design flows of lockable joints, modular limbs, and reconfigurable PKMs. With regard to the kinematic analysis of Exechon-like PKMs, the degrees of freedom(DoF)and singularities were analyzed with the screw theory, wherein the screw systems of the Exechon-like PKMs were formulated and overfull Jacobian matrices of the PKMs were derived. Loop-closure equations were formulated to develop the inverse kinematic model and parasitic motions of the moving platform. The reachable workspaces of the proposed PKMs were predicted by a "sliced partition" algorithm. A comparative analysis of the kinematics shows that the reconfigurable design of the Exechon-like PKMs can keep the DoF of the PKMs and their architectural singularities unchanged. The analysis also shows that the reconfigurable design can significantly improve the complexity of the parasitic motions of inverse kinematics and the distributions of the moving platform's reachable workspaces for several Exechon-like PKMs. Finally, using the 3D printing technology, a laboratory prototype of Exe-Ⅰ PKM was built to conduct the kinematic experiment. The experimental values agree well with the theoretical values. The absolute error is less than ±0.4 mm and the relative error is within 3.2%, which verifies the effectiveness of the proposed kinematic analysis module. The conceptual designs of reconfigurable and modular PKMs in this study can prove to be key techniques to realize efficient reconfigurable designs and engineering applications of Exechon-like PKMs. © 2019, Editorial Board of Journal of Tianjin University(Science and Technology). All right reserved.