Type synthesis of multi-mode mobile parallel mechanisms based on refined virtual chain approach

Mechanisms with multiple operation and multiple locomotion modes are applied to implementing the different tasks and adapting to the changes in terrains as well. Based on this application, this paper presents a refined virtual chain approach which is applied to the type synthesis of a class of multi-mode mobile parallel mechanisms (PMs). This approach is based on screw theory to synthesize the branches with coaxial rotating components under different constraint conditions. The geometric orientations of the different constraint conditions in a plane can be changed by using coaxial rotating components. Meanwhile, the inactive joints in branches are determined. By means of this approach, a number of symmetrical and asymmetrical reconfigurable PMs with four branches are obtained. The four of the multi-mode PMs are sketched as examples and the operation and locomotion modes for the mechanisms are discussed.