Precise positioning of collaborative robotic manipulators using hand-guiding

Hand-guiding is a key feature of collaborative robots, allowing unskilled users to interact with them in an intuitive manner. This physical interface is extensively used for robot positioning during the human–robot interactive process. However, end-effector (EEF) precise and smooth positioning is still difficult to achieve by hand-guiding. This study extends and improves a previously proposed precision hand-guiding method at the EEF level. From the force/torque applied by the user at the EEF, the hand-guiding force/moment is calculated after compensating for the weight/inertia of the EEF. The proposed control solution is inspired by the motion properties of a passive mechanical system subjected to Coulomb/viscous friction. As a result, the human co-worker can control the linear/angular motion of the decoupled EEF. To ensure that the robot does not exceed its joints limits while hand-guided, a solution to scale down the linear/angular velocity of the EEF near the joints limits is integrated into the control strategy. Several experimental tests demonstrated the system performance considering positioning precision, joints limits avoidance, intuitiveness of use and motion smoothness (robot vibrations while hand-guided). A programming by demonstration application using the proposed method is also presented and discussed.