Kinematic Analysis of a Serial-Parallel Hybrid Mechanism and its Application to a Wheel-Legged Robot

A three-DOF (degree-of-freedom) serial-parallel hybrid mechanism is proposed that consists of a 2-UPS+U component (UPS: universal-/prismatic-/spherical-joint chain and U: universal joint) and an R+RPS component (R: revolute joint and RPS: revolute-/prismatic-/spherical-joint chain). This mechanism can provide high precision and a large workspace, which indicates its applicability to wheel-legged robots. To verify our proposal, a mobility analysis showed that the mechanism simultaneously achieved three rotational movements. Then, the inverse/forward position analysis, velocity analysis, acceleration analysis, and stiffness analysis were carried out. Finally, a prototype of the mechanism was fabricated and its position error was found to be <; 1.8% despite the large workspace. These results demonstrate the effectiveness of our proposal and provide a new approach for designing new mechanisms for wheel-legged robots.