A robotic system includes a jointed mechanism, position sensors, and a controller. The mechanism has an end-effector, and further includes actively-controlled joints and passive joints that are redundant with the actively-controlled joints. The position sensors are operable for measuring joint positions of the passive joints. The controller is in communication with the position sensors, and is programmed to execute a method to selectively control the actively-controlled joints in response to the measured joint positions using force control and/or a modeled impedance of the robotic mechanism. Possible control modes in impedance control include an Autonomous Mode in which an operator does not physically interact with the end-effector and a Cooperative Control Mode in which the operator physically interacts with the end-effector.