Stiffness characteristics and kinematics analysis of two‐link elastic underactuated manipulators

This article investigates the stiffness characteristics of two‐link underactuated manipulators, examines the effect on the torque resulting in the passive joint, and develops a stiffness model in analysing the behaviors of the manipulators. The kinematic analysis leads to the trajectory of the end‐effector, which is associated with the stiffness coupled between the active and passive joints and with the constraint forces, and the kinematic coupling is shown in the angular displacement and in the resulting torque. The stiffness characteristics are illustrated in the directional stiffness mapping, which gives a quantitative measure of stiffness with respect to displacement direction.