Abstract-NASA and General Motors have developed the second generation Robonaut, Robonaut 2 or R2, and it is scheduled to arrive on the International Space Station in late 2010 and undergo initial testing in early 2011. This state of the art, dexterous, anthropomorphic robotic torso has significant technical improvements over its predecessor making it a far more valuable tool for astronauts. Upgrades include: increased force sensing, greater range of motion, higher bandwidth and improved dexterity. R2's integrated mechatronics design results in a more compact and robust distributed control system with a faction of the wiring of the original Robonaut. Modularity is prevalent throughout the hardware and software along with innovative and layered approaches for sensing and control. The most important aspects of the Robonaut philosophy are clearly present in this latest model's ability to allow comfortable human interaction and in its design to perform significant work using the same hardware and interfaces used by people. The following describes the mechanisms, integrated electronics, control strategies and user interface that make R2 a promising addition to the Space Station and other environments where humanoid robots can assist people.

Abstract-The second generation Robonaut hand has many advantages over its predecessor. This mechatronic device is more dexterous and has improved force control and sensing giving it the capability to grasp and actuate a wider range of tools. It can achieve higher peak forces at higher speeds than the original.Developed as part of a partnership between General Motors and NASA, the hand is designed to more closely approximate a human hand.Having a more anthropomorphic design allows the hand to attain a larger set of useful grasps for working with human interfaces. Key to the hand's improved performance is the use of lower friction drive elements and a redistribution of components from the hand to the forearm, permitting more sensing in the fingers and palm where it is most important. The following describes the design, mechanical/electrical integration, and control features of the hand. Lessons learned during the development and initial operations along with planned refinements to make it more effective are presented.

-Balance maintenance and upright posture recovery under unexpected environmental forces are key requirements for safe and successful co-existence of humanoid robots in normal human environments. In this paper we present a two-phase control strategy for robust balance maintenance under a force disturbance. The first phase, called the reflex phase, is designed to withstand the immediate effect of the force. The second phase is the recovery phase where the system is steered back to a statically stable "home" posture. The reflex control law employs angular momentum and is characterized by its counter-intuitive quality of "yielding" to the disturbance. The recovery control employs a general scheme of seeking to maximize the potential energy and is robust to local ground surface feature. Biomechanics literature indicates a similar strategy in play during human balance maintenance.Index Terms -Biped robot, disturbance rejection, balance, posture recovery, potential energy. MOTIVATIONFuture humanoid robots are expected to freely reside within common human environments and to be physically more interactive with their surroundings. A key factor for their successful co-existence with humans lies in their capacity to withstand unexpected perturbations without the loss of balance. A failed postural recovery may result in a fall which can badly damage the machine itself and/or injure people in the vicinity. We wish to develop a control strategy such that biped robots can appropriately respond to unknown force disturbances from the surroundings. This paper focuses on the specific problem of balance maintenance during upright stance which is to be distinguished from balance maintenance during gait. We take our cue from biomechanics research [10] which points out the very different nature of the two apparently related problems and how human beings employ specific control strategies to deal with them.We recognize two main phases during a balance maintenance scenario. The first phase is the reflex phase in which the body generates a rapid movement to quickly absorb a disturbance force. As the disturbance force subsides, the body attempts to recover its original posture. This is called the recovery phase.In accordance with these two phases of the balance maintenance scenario, we employ a two-phase control strategy, the Reflex-Recovery Strategy. The reflex controller rapidly generates an increase in angular momentum to correctly compensate for the destabilizing effect of the disturbance. In doing so it accepts a posture deviation. The objective of the recovery controller is to compensate for this postural deviation.Biomechanical studies indicate that human beings adopt a similar strategy in response to an unexpected perturbation [10,11,16]. As shown in Fig. 1, the immediate response to a difficult disturbance is to rotate forward about the hip to absorb the disturbance. Once comfortable, the forward rotation stops and the body returns to a statically stable upright posture.Our dynamic analysis explains the interesting but c...

Abstract-Impedance control is well-suited to robot manipulation applications because it gives the designer a measure of control over how the manipulator to conforms to the environment. However, in the context of end-effector impedance control when the robot manipulator is redundant with respect to end-effector configuration, the question arises regarding how to control the impedance of the redundant joints. This paper considers multi-priority impedance control where a secondpriority joint space impedance operates in the null space of a first-priority Cartesian impedance at the end-effector. A control law is proposed that realizes both impedances while observing the priority constraint such that a weighted quadratic error function is optimized. This control law is shown to be a generalization of several motion and impedance control laws found in the literature. The paper makes explicit two forms of the control law. In the first, parametrization by passive inertia values allows the control law to be implemented without requiring end-effector force measurements. In the second, a class of parametrizations is introduced that makes the null space impedance independent of end-effector forces. The theoretical results are illustrated in simulation.

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