| Human-centered robotics involves the close interaction between robotic systems and human beings, including direct human-manipulator contact. In such applications, we must consider the requirements of safety in addition to traditional performance metrics. While there has been significant progress in manipulator and actuator design, there has yet to be a successful manipulator design that possesses the characteristics of both safety and performance.; To address this need, a new actuation method, referred to as Distributed Macro-Mini actuation (DM2), has been developed. Recognizing that manipulator torque requirements, as a function of frequency, fall-off sharply at higher frequencies, the DM2 approach partitions the actuation into separate macro- and mini-actuators that provide the low- and high-frequency torques, respectively. Locating the actuators at arm locations where they are most effective, referred to as distributed actuation, is an essential feature of this new approach. Large, macro actuators provide the low-frequency torque required to compensate gravity and provide acceleration torques. Locating the macro actuators at the base of a manipulator reduces the size and weight of the manipulator substantially. The use of a compliant element between the macro actuator and drive-train decouples the reflected inertia of the macro actuator from the manipulator, further reducing the effective inertia. To recover high-frequency torque capability, the mini actuators are collocated at the joints, providing the high mechanical bandwidth necessary for high performance tasks. Because the required high-frequency torque magnitude is small, the mini motors can be kept small enough so that they contribute only a minor increase in manipulator size and weight.; Using a two-axis testbed, the DM2 approach was evaluated for impact behavior, position tracking performance, force tracking performance, and haptic performance. Experimental results demonstrated that by drastically reducing the effective inertia of the manipulator, while maintaining high-frequency torque capability, the competing design requirements of performance and safety can be successfully integrated into a single manipulation system.; Finally, an extension to multi-degree-of-freedom manipulator control is presented in the form of a six-degree-of-freedom robot composed of a torso with two three-degree-of-freedom manipulators arranged in an anthropomorphic configuration. A description of the design and fully-assembled hardware is included. |
