Enhanced Hybrid Position and Admittance Control Based on Nonholonomic Wheeled Mobile Manipulator with Redundancy

Due to the advantage of combining mobility, manipulability and high efficiency, the nonholonomic wheeled mobile manipulators (NWMM) have been widely applied in numerous applications. However, the combination of manipulator and mobile platform brings new challenges in force exertion capacity, location precision and the redundancy problem of inverse kinematics. This paper proposes a method to improve the force exertion capability while executing tasks for which the mobile manipulator has kinematic redundancy. Redundancy resolution is formulated as optimal problem subject to carefully designed constraints. The entire framework is implemented under the hybrid position and admittance control (HPAC) for end-effector. Experiments on a two-wheeled nonholonomic mobile manipulator verified the feasibility of the proposed control strategy. The advantage of the force exertion enhancement (FEE) is also verified through comparing the joint efforts.