Lightweight compliant arm with compliant finger for aerial manipulation and inspection

This paper presents the design and experimental validation of a compliant and lightweight 3-DOF robotic arm - shoulder yaw, shoulder pitch and elbow pitch joints - equipped with a compliant finger module intended for aerial inspection and manipulation in contact with the environment. A simple transmission mechanism consisting in a pair of compression springs and a flange bearing is integrated in the shoulder pitch and elbow pitch joints between the servo shaft and the output frame. Joint deflection measurement with potentiometer allows joint torque but also contact force estimation and control. The low stiffness of the compliant finger has been exploited for soft collision detection and obstacle localization, in such a way that the contact forces do not significantly disturb the UAV. Fixed-base experiments have been performed with the arm, including the characterization of the compliant joints and the control of the contact force at wrist point.