Workspace and force-moment transmission of a variable arm type parallel manipulator

Kinematic and dynamic characteristics of Stewart platform based parallel manipulators are fixed once they are constructed. Thus parallel manipulators with various configurations are required to meet a variety of applications. In this research a variable arm type parallel manipulator (VAPM) was developed, in which the length of the arm linking the platform center to the platform-leg contact point can be varied by the actuator. Workspace of the VAPM is larger than that of a traditional Stewart platform and especially the range in which the maximum orientation angles can be maintained is significantly expanded. Furthermore, the characteristics of force and moment transmission between the legs and platform can be adjusted to meet the requirements of various tasks. Kinematic and dynamic analysis was performed to verify the usefulness of the VAPM and the actual hardware was built to demonstrate the feasibility.