Precise hand-guiding of redundant manipulators with null space control for in-contact obstacle navigation

Rand-guiding of collaborative redundant manipulators allows an unskilled user to interact and program the robot intuitively. Many industrial applications require precise positioning at the end-effector (EEF) level inside cluttered environments, where manipulator's redundancy is required. Yet, the potentialities of redundancy while hand-guiding at EEF level are not fully explored. This paper addresses the subject of precision in hand-guiding at EEF level while using the redundancy for in-contact obstacle navigation. In the presence of a contact with an obstacle, the proposed null space control method actuates in a way that the manipulator slides compliantly with its structure on the body of the obstacle while preserving the precision of the hand-guiding motion at EEF level. Force/torque (FT) data from a FT sensor mounted at the robot flange are the input for EEF precision hand-guiding while the torque data from the joints of the manipulator represent the contact between robot structure and obstacles. Experimental tests were carried out successfully using a KUKA iiwa industrial manipulator with 7 degrees of freedom (DOF). Where, the EEF is hand-guided on a straight line while the robot is sliding on the obstacle with its structure, results indicate the precision of the proposed method.