A Pneumatically-Actuated Variable-Stiffness Robot Arm Using Parallel Flexures

A novel design is presented for a variable-stiffness robotic arm from conceptual design to experimental validation, utilizing a fast-acting pneumatic rodless cylinder with minimal footprint. Unlike other systems previously developed that rely on variation of compliance in kinematic joints, the proposed design enables the manipulator arm itself to undergo stiffness change by controlling the effective length of two parallel sheet flexures. The behavior is modeled using traditional beam bending equations. The concept is validated using finite element analysis and experiments. Quick and accurate stiffness change is demonstrated using static and dynamic calibration of the system. The overall change in stiffness for static applications is about lO-fold, and it can be achieved in about 0.6 seconds. The ability of the controller to track stiffness profiles over time is also demonstrated through experiments. We envision that the presented variable-stiffness robotic arm can be cascaded for accommodating three axes of impacts, for building multi-linked collaborative manipulators.