Redundant robotic systems provide great challenges in solving kinematics and control problems, that are yet also open opportunities for exploring new, diverse and intelligent ideas and methods. In this paper, an advanced control method is proposed for position control problems of redundant robots with output constraints. The controller is structured with two control layers. In the high-level control layer, a cost function is first synthesized from the main control objective under constraint conditions. Virtual control signals are then reckoned to optimize the cost function using a soft Momentum-Levenberg-Marquardt approach. To realize the high-level control command, a nonlinear control signal is employed in the low-level control layer throughout a new nonsingular terminal sliding mode control structure. Comparative simulation results verified on a 7-DOF robotic arm model confirmed the effectiveness of the proposed control algorithm.