G. Hirzinger's research while affiliated with German Aerospace Center (DLR) and other places

Orbital robotics is receiving growing attention worldwide for applications in servicing and repositioning of partially or fully defective satellites. In this paper, we present the scope and main results of a four-year research project, which aimed at developing necessary robotic technologies for such applications. The scope is two-fold, since we address both the human-operated robotic operational mode, referred to in robotics as force-feedback teleoperation, as well as the alternative autonomous mode, for the specific task of approaching and grasping a free-tumbling target satellite. We present methodological developments and experimental as well as numerical validations in the fields of tele-communications, computer vision, robot and spacecraft control and system identification. The results of this work constitute important advances in the fundamental building blocks necessary for the orbital applications of interest.

This paper describes a novel method for motion generation and reactive collision avoidance. The algorithm performs arbitrary desired velocity profiles in absence of external disturbances and reacts if virtual or physical contact is made in a unified fashion with a clear physically interpretable behavior. The method uses physical analogies for defining attractor dynamics in order to generate smooth paths even in presence of virtual and physical objects. The proposed algorithm can, due to its low complexity, run in the inner most control loop of the robot, which is absolutely crucial for safe Human Robot Interaction. The method is thought as the locally reactive real-time motion generator connecting control, collision detection and reaction, and global path planning.

In autonomous bimanual operation of a robot, parallelized planning and execution of a task is essential. Elements of a task have different functional and spatial relationships. They may depend on each other and have to be executed in a specific order or they may be independent and their order can be determined freely. Consequently, individual actions can be planned and executed in parallel or not. In a proof of concept, this paper shows that the structure of a task and its mapping onto subordinate planners can significantly influence planning speed and task execution. Independent tasks are planned using two parallel path planners. Dependent tasks are planned using one path planner for both arms. Using a simple, yet expandable experimentation scenario, the resulting recommendations for parameterizing path planners are verified on a humanoid robot. For execution on the real robot a violation of the rigid body model used in path planners had to be addressed.

In this paper we present various new insights on the effect intrinsic joint elasticity has on safety in pHRI. We address the fact that the intrinsic safety of elastic mechanisms has been discussed rather one sided in favor of this new designs and intend to give a more differentiated view on the problem. An important result is that intrinsic joint elasticity does not reduce the Head Injury Criterion or impact forces compared to conventional actuation with some considerable elastic behavior in the joint, if considering full scale robots. We also elaborate conditions under which intrinsically compliant actuation is potentially more dangerous than rigid one. Furthermore, we present collision detection and reaction schemes for such mechanisms and verify their effectiveness experimentally.

This paper introduces the mechatronic design of the X-Arm-2 haptic exoskeleton. The X-Arm-2 is a new and fully actuated force-reflecting human arm exoskeleton, based on our previously proposed ergonomic kinematic exoskeleton structure [1]. The X-Arm-2 is the result of an overall research effort on ergonomic haptic wearable devices [2]. This effort has led to a power-dense haptic device design that is explicitly human-centered. The X-Arm-2 can a) interact with varying operator arm sizes without requiring adjustments (5 th-95 th %-ile range for Astronaut crew), b) provide crisp force-feedback performance through a human-oriented scaling and implementation of actuators and torque sensors, c) interact with the full workspace of the human limb without limiting natural movement and without creating interface forces [3] and d) has a low overall mass (without motor drivers) of only 6.2 kg. The inertia of its movable structure was minimized by relocating some of its most powerful drives via Bowden cable transmissions [4].

Mobile platforms equipped with several steering wheels are known to be omnidirectional, i.e., able to independently translate and rotate on the plane. As an improvement to this design, the Justin mobile platform also possesses the ability to vary its footprint over time by extending/retracting the wheel legs during motion. In this paper, we discuss the kinematic modeling and control issues for such a platform. The goal is to obtain a tracking controller which is able to realize an arbitrary linear/angular platform motion while, at the same time, independently expanding/retracting each leg. Experimental results support the proposed approach.

This paper introduces the planning and control software of a teleoperation system for research in minimally invasive robotic surgery. It addresses the problem of how to organize a complex system with 41 degrees of freedom as a flexible configurable platform. Robot setup planning, force feedback control and nullspace handling with three robotic arms are considered. The planning software is separated into sequentially executed planning and registration procedures. An optimal setup is first planned in virtual reality and then adapted to variations in the operating room. The real time control system is structured in hierarchical layers. Functions are arranged in the layers with respect to their domain and maximum response time. The design is flexible and expandable while performance is maintained. Structure, functionality and implementation of planning and control are described. The prototypic robotic system provides intuitive bimanual bilateral teleoperation within the planned working space.