Search

Two people with long-standing tetraplegia use neural interface system-based control of a robotic arm to perform three-dimensional reach and grasp movements. John Donoghue and colleagues have previously demonstrated that people with tetraplegia can learn to use neural signals from the motor cortex to control a computer cursor. Work from another lab has also shown that monkeys can learn to use such signals to feed themselves with a robotic arm. Now, Donoghue and colleagues have advanced the technology to a level at which two people with long-standing paralysis — a 58-year-old woman and a 66-year-old man — are able to use a neural interface to direct a robotic arm to reach for and grasp objects. One subject was able to learn to pick up and drink from a bottle using a device implanted 5 years earlier, demonstrating not only that subjects can use the brain–machine interface, but also that it has potential longevity. Paralysis following spinal cord injury, brainstem stroke, amyotrophic lateral sclerosis and other disorders can disconnect the brain from the body, eliminating the ability to perform volitional movements. A neural interface system1,2,3,4,5 could restore mobility and independence for people with paralysis by translating neuronal activity directly into control signals for assistive devices. We have previously shown that people with long-standing tetraplegia can use a neural interface system to move and click a computer cursor and to control physical devices6,7,8. Able-bodied monkeys have used a neural interface system to control a robotic arm9, but it is unknown whether people with profound upper extremity paralysis or limb loss could use cortical neuronal ensemble signals to direct useful arm actions. Here we demonstrate the ability of two people with long-standing tetraplegia to use neural interface system-based control of a robotic arm to perform three-dimensional reach and grasp movements. Participants controlled the arm and hand over a broad space without explicit training, using signals decoded from a small, local population of motor cortex (MI) neurons recorded from a 96-channel microelectrode array. One of the study participants, implanted with the sensor 5 years earlier, also used a robotic arm to drink coffee from a bottle. Although robotic reach and grasp actions were not as fast or accurate as those of an able-bodied person, our results demonstrate the feasibility for people with tetraplegia, years after injury to the central nervous system, to recreate useful multidimensional control of complex devices directly from a small sample of neural signals.

This paper presents impedance controllers with adaptive friction compensation for the five-finger dexterous robot hand DLR-HIT II in both joint and Cartesian space. An FPGA-based control hardware and software architecture with real-time communication is designed to fulfill the requirements of the impedance controller. Modeling of the robot finger with flexible joints and mechanical couplings in the differential gear-box are described in this paper. In order to address the friction due to the complex transmission system and joint coupling, an adaptive model-based friction estimation method is carried out with an extended Kalman filter. The performance of the impedance controller with both adaptive and parameter-fixed friction compensations for the robot hand DLR-HIT II are analyzed and compared in this paper. Furthermore, gravity estimation is implemented with Least Squares technique to address uncertainties in gravity compensation due to the close proximity and complexity of robot hand components. Experimental results prove that accurate position tracking and stable torque/force response can be achieved with the proposed impedance controller with friction compensation on five-finger dexterous robot hand DLR-HIT II.

Research on surgical robotics demands systems for evaluating scientific approaches. Such systems can be divided into dedicated and versatile systems. Dedicated systems are designed for a single surgical task or technique, whereas versatile systems are designed to be expandable and useful in multiple surgical applications. Versatile systems are often based on industrial robots, though, and because of this, are hardly suitable for close contact with humans. To achieve a high degree of versatility the Miro robotic surgery platform (MRSP) consists of versatile components, dedicated front–ends towards surgery and configurable interfaces for the surgeon. This paper presents MiroSurge, a configuration of the MRSP that allows for bimanual endoscopic telesurgery with force feedback. While the components of the MiroSurge system are shown to fulfil the rigid design requirements for robotic telesurgery with force feedback, the system remains versatile, which is supposed to be a key issue for the further development and optimisation.

A high-performance airborne water vapor differential absorption lidar has been developed during the past years. This system uses a four-wavelength/three-absorptionline measurement scheme in the 935 nm H2O absorption band to cover the whole troposphere and lower stratosphere simultaneously. Additional high spectral resolution aerosol and depolarization channels allow precise aerosol characterization. This system is intended to demonstrate a future space-borne instrument. For the first time, it realizes an output power of up to 12 W at a high wall-plug efficiency using diode-pumped solid-state lasers andn onlinear conver-sion techniques. Special attention was given to a rugged optical layout. This paper describes the system layout and technical realization. Key performance parameters are given for the different subsystems.

The article "High-Performance Numerical Software for Control" concerns the development of quality software for control applications that perform efficiently and reliably on today'S modern computing machines. In particular, the subroutine library SLICOT is described. This library is the main outcome of the European project NICONET. The article gives the background and motivation for the development of this library and describes its most important features. SLICOT is freely available for nuncommercial use and provides many powerful user-callable routines for solving complex system analysis and control design tasks. Today SLICOT can be considered a synonym for reliable numerical algorithms, efficient computation, and robust numerical software for systems and control.

In this paper, we give a numerically reliable algorithm to compute the zeros of a periodic descriptor system. The algorithm is a variant of the staircase algorithm applied to the system pencil of an equivalent lifted time-invariant state-space system and extracts a low-order pencil which contains the zeros (both finite and infinite) as well as the Kronecker structure of the periodic descriptor system. The proposed algorithm is efficient in terms of complexity by exploiting the structure of the pencil and is exclusively based on orthogonal transformations, which ensures some form of numerical stability.

We propose a numerically reliable computational approach to design least order fault detectors using descriptor system techniques. This approach is based on a new numerically stable algorithm to compute least order rational null space bases of rational matrices. The main computation in this algorithm is the onhogonal reduction of the system pencil matrix to a Kronecker-like form. The proposed approach can be combined with coprime factorization techniques to determine stable rational bases. Least order fault detectors can be detennined by selecting an appropriate linear combination of basis vectors by eliminating non-essential dynamics. The proposed approach is applicable to both standard and descriptor system descriptions.

The efficient solution of a class of controller approximation problems by using frequency-weighted balancing related model reduction approaches is considered. It is shown that for certain standard performance and stability enforcing frequency-weights, the computation of the frequency-weighted controllability and observability grammians can be done by solving reduced order Lyapunov equations regardless the controller itself is stable or unstable. The new approach can be used in conjunction with accuracy enhancing square-root and balancing-free techniques recently developed by the authors for the frequency-weighted balancing related model reduction.

The application of the parameter space method has proven to be useful for robustness analysis of uncertain parametric systems and robust control synthesis for quite a number of applications. However, it has been restricted to linear systems and the consideration of eigenvalue criteria. This paper enhances the application of the parameter space method to include various locus criteria. This allows not only for incorporation of linear criteria (e. g. gain and phase margin) but for nonlinear criteria as well (e.g. Popov- or circle criterion and the dual locus method).

A computational approach is proposed to solve the minimum norm and/or robust pole assignment problem for linear periodic discrete-time systems. The proposed approach uses a periodic Sylvester equation based parametrization of the periodic pole assignment problem and exploits the non-uniqueness of the problem by imposing conditions on the norm of the resulting periodic state feedback and/or on the condition numbers of the periodic eigenvector matrices of the closed-loop system. The solution method relies on using gradient search methods on suitably defined cost functions. Explicit expression of the gradients of cost functions are derived and the efficient evaluation of the cost functions and gradients is discussed. Numerical examples illustrate the effectiveness of the proposed approach.

After decades of theoretical study in physiology and neurology communities, the paradigm of muscle synergies is now being explored in rehabilitation robotics as a strategy to control mechanical artifacts with many degrees-of-freedom (DoF) in a simple yet effective and human-like way. In particular, muscle synergies during grasping and in graded-force tasks are of great interest for the control of dexterous hand prostheses. To this end, we have designed and tested a novel device to accurately and simultaneously measure fingertip forces. The device, called FFLS (Finger-Force Linear Sensor), measures the forces applied by the human fingertips in both directions (flexion and extension of index, middle, ring and little finger plus thumb rotation and abduction/adduction). It is suited for several different hand sizes, enforces high accuracy in the measurement and its signal is guaranteed to be linear in a high range of forces (100N in both directions for each finger). It outputs six analog voltages (+/-10V), suited for processing with a DAQ card.

Reactively dealing with self-collisions is an important requirement on multidegree-of-freedom robots in unstructured and dynamic environments. Classical methods to integrate respective algorithms into task hierarchies cause substantial problems: Either these unilateral safety constraints are permanently active, unnecessarily locking DOF for other tasks, or they get activated online and result in a discontinuous control law. We propose a new, reactive self-collision avoidance algorithm for highly complex robotic systems with a large number of DOF. In particular, configuration-dependent damping is imposed to dissipate undesired kinetic energy in a well-directed manner. Moreover, we merge the algorithm with a novel method to incorporate these unilateral constraints into a dynamic task hierarchy. Our approach both allows us to specifically limit the force/torque derivative to comply with physical constraints of the real robot and to prevent discontinuities in the control law while activating/deactivating the constraints. No redundancy is wasted. No comparable algorithms have been developed and implemented on a torque-controlled robot with such a level of complexity so far. The implementation of our generic solution on the multi-DOF humanoid Justin clearly validates the performance and demonstrates the real-time applicability of our synthetic approach. The proposed method can be used to contribute to whole-body controllers.

An overview of mathematical modelling of the human hand is given. We consider hand models from a specific background: rather than studying hands for surgical or similar goals, we target at providing a set of tools with which human grasping and manipulation capabilities can be studied, and hand functionality can be described. We do this by investigating the human hand at various levels: (1) at the level of kinematics, focussing on the movement of the bones of the hand, not taking corresponding forces into account; (2) at the musculotendon structure, i.e. by looking at the part of the hand generating the forces and thus inducing the motion; and (3) at the combination of the two, resulting in hand dynamics as well as the underlying neurocontrol. Our purpose is to not only provide the reader with an overview of current human hand modelling approaches but also to fill the gaps with recent results and data, thus allowing for an encompassing picture.

This paper presents a new method to calculate and display an approximated workspace of a surgical robot in nearly realtime. Displaying this information on a screen in the operation room could support the surgeon during intraoperative trocar placement for teleoperated minimally invasive robotic surgery (MIRS). We give a short overview on existing trocar placement procedures in teleoperated MIRS and describe the possibilities and limitations of workspace analysis methods to support the surgeon during trocar placement. Our new method uses MIRS-specific simplifications to reduce the search space and enable the creation of a reduced workspace map. It was implemented for the DLR MiroSurge system. The implementation can create a reduced workspace map and display a mesh representation of the map in less than 2 seconds. We give a short outlook on how this method could be embedded in trocar placement procedures in the operation theater and what our future plans are with this method.

We present a general real-time continuous collision detection algorithm for arbitrary systems of moving bodies connected to each other in a kinematic tree of joints. Here “joint” as a general term refers to the measured relative motion between two bodies, which may be physically connected or not. We provide a basic set of joints covering revolute and prismatic joints, vehicle motion, and 3d positioning which is sufficient for many applications in particular those involved with mobile manipulators, e.g. industrial and humanoid robots, intelligent transportation systems, or equipment at construction sites. Each joint implementation either operates on a motion bound (an interval covering the braking distance) or an uncertainty bound (measurement error) and computes a volume that spatially bounds the effect of that motion or uncertainty. Aggregating all joints in a kinematic tree then yields a conservative continuous collision detection for the complex and uncertain motion of the whole system. We further present an augmented reality visualization that overlays the collision volumes into the live image of a camera, which can be used to validate the collision model before bringing a system into service.

In this paper, we demonstrate methods for bipedal walking control based on the Capture Point (CP) methodology. In particular, we introduce a method to intuitively derive a CP reference trajectory from the next three steps and extend the linear inverted pendulum (LIP) based CP tracking controller introduced in [1], generalizing it to a model that contains vertical CoM motions and changes in angular momentum. Respecting the dynamics of general multibody systems, we propose a measurement-based compensation of multi-body effects, which leads to a stable closed-loop dynamics of bipedal walking robots. In addition we propose a ZMP projection method, which prevents the robots feet from tilting and ensures the best feasible CP tracking. The extended CP controller’s performance is validated in OpenHRP3 [2] simulations and compared to the controller proposed in [1].

Intrinsically elastic robots, which technically implement some key characteristics of the human muskoskeletal system, have become a major research topic in nowadays robotics. These novel devices open up entirely new control approaches. They base on temporary storage of potential energy and its timed transformation into kinetic energy. In legged locomotion, such considerations have been a common tool for unveiling the respective fundamental physical processes. However, in arm control, elasticities were typically considered parasitic. In this video we outline our efforts in exploiting the inherent capabilities of intrinsically elastic robots in order to bring them closer to human performance. Instead of applying purely kinematic learing-by-demonstration approaches, which are certainly suboptimal, we argue for using model based techniques in order to optimally exploit the system dynamics such that highly dynamic motion and manipulation capabilities can be achieved. In particular, the explicit use of elasticities as temporary energy tanks can be fully exploited, if they are modeled adequately as an integral part of the mechanism. We also believe that such approaches can substantially contribute to the understanding of human motion biomechanics.

We present a method for transferring grasps between objects of the same functional category. This transfer is intended to preserve the functionality of a grasp constructed for one of the objects, thus enabling the analogous action to be performed on a novel object for which no grasp has been specified. Manipulation knowledge is hence generalized from a single example to a class of objects with a significant amount of shape variability. The transfer is achieved through warping the surface geometry of the source object onto the target object, and along with it the contact points of a grasp. The warped contacts are locally replanned, if necessary, to ensure grasp stability, and a suitable grasp pose is computed. We present extensive results of experiments with a database of four-finger grasps, designed to systematically cover variations on grasping the mugs of the Princeton Shape Benchmark.

In this paper we introduce an adaptive control scheme for robots with elastic joints (in particular for the DLR medical robot) in order to increase the positioning accuracy and the performance of control with respect to uncertainties of the parameters of the robot dynamics. In order to design control and analyze system stability a static friction model is applied which describes Coulomb, viscose and load dependent friction. A stability analysis is done for this adaptive control scheme, allowing a Lyapunov based convergence analysis in the context of the nonlinear robot dynamics. Experimental results validate the practical efficiency of the approach.

Early system error detection is essential for safe human-robot interaction. Detecting errors in the large amount of sensory and status data is, however, difficult, especially since the amount of fault data is very small if at all available; a problem for which no sufficiently stable methods exist. This thesis introduces a new Robot Anomaly Detection System (RADS) consisting of a multi-stage solution, that adapts to high dimensional input and detects errors without previous records of them. Application to real robot data proves its satisfying performance.

This thesis presents the design and construction of an Electromyography (EMG) high−density acquisition system prototype at the Deutschen Zentrums für Luft und Raumfahrt (DLR) Bionics group in Munich− Germany. It does not intend to come up with new principles of EMG recording, but its scope is to search, compare, simulate, construct and validate nowadays available solutions that fulfill the imposed requirements. The design consists in ten functional blocks that cover all the system aspects from the power supply to the measuring electrodes. In order to construct the circuit prototype, some classical solutions were implemented and some novelty configurations were explored, for instance: a novelty DC rejection filter without grounded resistors, to prevent degradation of the front−end amplifier Common Mode rejection (CMR) and the driven shields that solved the problem of amplifying the EMG signal at a considerable distance from the source. This document covers all the way in between the muscles and the computer, that EMG signals go through: electrodes, esd protection, shield cables, DC rejection, amplification, Driven Right Leg feedback, filtering, isolation and digitization.

We present a camera-based 3D feature tracking method, integrated into a bank of iterated, extended Kalman filters (IEKF), associated to each visual feature. The approach exploits motion field to estimate velocities of the rigid body. The depths are required only for initialization, and can be obtained either from joint estimation of depth and motion or from stereo correspondence. The motion of each 3D point cloud is predicted under a common rigid velocity constraint. A robust pose estimator, based on dual-quaternions and median statistics, is further applied to the estimated points. In case of temporarily missing measurements, the last estimated body velocity is used to predict the next poses. Results are shown on images of a satellite-mockup, to demonstrate performances for on-orbit servicing in space environment.

This paper introduces a new framework for task space telemanipulation. The TASK space grasping and MANipulation (TaskMan) concept utilizes a library of tasks based on gesture commands, which replaces the conventional mapping required between the human hand and the end effector. Task communication between the human machine interface (HMI) and the robot end effector requires two symbiotic but nonidentical state machines on the master and slave side. The task states on two sides are synchronized via a single channel communication, as opposed to multi-channel joint space or Cartesian mapped information. HAND gesture command for grasping and MANipulation (HandyMan) HMI command algorithm is proposed for the recognition of hand gestures, which incorporates a library of intuitive task gestures to be used by the teleoperator wearing a CyberGlove. The task gestures are used to drive the states of the TaskMan state machines. With the proposed concepts, this work has realized teleoperated grasp and manipulation with a 15-DoF robot hand in task space. Full 6-DoF of object manipulation was achieved with different grasp combinations, and demonstrated higher repeatability, success rate and easier operation compared to conventional joint space teleoperation methods.

We describe an ego-motion algorithm based on dense spatio-temporal correspondences, using semi-global stereo matching (SGM) and bilateral image warping in time. The main contribution is an improvement in accuracy and robustness of such techniques, by taking care of speed and numerical stability, while employing twice the structure and data for the motion estimation task, in a symmetric way. In our approach we keep the tasks of structure and motion estimation separated, respectively solved by the SGM and by our pose estimation algorithm. Concerning the latter, we show the benefits introduced by our rectified, bilateral formulation, that provides at the same time more robustness to noise and disparity errors, at the price of a moderate increase in computational complexity, further reduced by an improved Gauss-Newton descent.

Im Rahmen der vorliegenden Bachelorarbeit wurde ein Prüfstand für taktile Sensoren konzipiert und aufgebaut. Der Prüfstand ermöglicht die Verifizierung und den Vergleich neuartiger taktiler Sensorprototypen. Dies ermöglicht die Erforschung neuer Sensorwerkstoffe und Sensorgeometrien, sowie eine Kalibrierung erster Sensorprototypen durch die Aufnahme einer Kraft-/Widerstandskurve. Nach der Recherche ähnlicher Prüfverfahren für die Analyse der menschlichen Haut, wurden die dort verwendeten mechanischen Lösungsansätze auf ihre Eignung als Prüfstand für taktile Sensoren hin evaluiert. Unter Verwendung einer am Institut verfügbaren Zug-/Druckprüfmaschine des Herstellers Zwick/Roell konnten erste Kraftmessungen kompletter taktiler Sensorelemente durchgeführt werden. Die gewonnenen Messdaten dienten als Grundlage für die Auslegung eines Mehrachslinearsystems und dessen Antrieb. Unter Berücksichtigung der Vor- und Nachteile der möglichen Linearachskombinationen wurde ein Portalsystem mit drei Freiheitsgraden als Prüfstand entworfen. Hierfür wurden Lineareinheiten des Herstellers Misumi angefordert und passende Aktoren ausgewählt. Aufgrund von Lieferverzögerungen musste im zeitlichen Rahmen der Bachelorarbeit auf eine kleinere Lineareinheit zurückgegriffen werden. Mit dieser war die Realisierung der verschiedenen Prüfarten mechanisch, wie auch elektrisch und softwaretechnisch möglich. Nach der Fertigstellung einer Benutzeroberfläche unter Zuhilfenahme der grafischen Programmier-Software LabVIEW konnten erste Prüfversuche durchgeführt werden. Die implementierten Prüfvarianten funktionierten während den gefahrenen Messungen erwartungsgemäß und stellten die Funktion des Prüfstandes unter Beweis

In dieser Bachelorarbeit wird die Weiterentwicklung einer bestehenden Auswerteelektronik für polymerbasierte taktile Sensoren zu einem Sensorsystem beschrieben. Den Kern dieser Arbeit stellt die Minimierung des Raumbedarfs der elektronischen Schaltung durch Verwendung von modernen Fertigungstechniken, sowie die Erweiterung deren sensorischer Fähigkeiten dar. Desweiteren wird mit den Konzepten dieser Arbeit die Grundlage, seitens des Sensorsystems, für die Kommunikation zwischen einem taktilen Sensorsystem und den Schnittstellen einer Robotersteuerung geschaffen.

Solving arbitrary manipulation tasks is a key feature for humanoid service robots. However, especially when tasks involve handling complex mechanisms or using tools, a generic action description is hard to define. Different objects require different handling methods. Therefore, we try to solve manipulation tasks from point of view of the object, rather than in the context of the robot. Action templates within the object context are introduced to resolve object specific task constraints. As part of a centralized world representation, the action templates are integrated into the planning process. This results in an intuitive way of solving manipulation tasks. The underlying architecture as well as the mechanisms are discussed within this paper. The proposed methods are evaluated in two experiments.

The development of anthropomorphic robotic grippers requires profound knowledge about the functionality of the human hand. For investigating its kinematic and dynamic properties, numerous biomechanical models have been established based on the assumption of fixed rotational axes. Even though this approach has proven to be accurate for most joints of the hand, difficulties have been reported for modelling the movement of the thumb. In order to investigate errors resulting from the thumb carpo-metacarpal joint, a new modelling approach is pursued that is based on contacting surfaces and stabilizing tissues. The joint is modelled as a multi-body system and driven by forces exerted by the cartilage contact, ligaments and muscles. Comparing the simulation results to anatomical literature reveals the capabilities of the proposed approach, but also the necessity of further improvements for its applicability in biomechanical investigations.

Grasp quality measures have been studied for long time, given their importance to evaluate the goodness/convenience of a grasp made with a robotic hand. However, the application of these quality measures to the grasps made by humans has just recently received some attention. This paper presents an experimental evaluation and comparison of different measures, using data obtained with a sensorized object. The experiment compares power grasps and precision grasps obtained with different number of fingers. The results intend to be a guide to the application of such qualities in the evaluation of robotic grasp actions.

There are assembly tasks which require a compliant device at the end-effector since possible disturbances are beyond the bandwidth of robot control. This paper discusses a compliant force-torque sensor for assembly. Two aspects are explained in detail: Force control considering a significant force dependent displacement, and control of an end-effector with an elastic mounting during fast unconstrained motion. The latter uses an adaptive scheme which serves as a further level in a hierarchical position-based control. Experimental results are given which show the limits of industrial robots.

A different way of force control is presented, that is especially advantageous for position controlled robots. Instead of usual force control laws we rely on the well tuned position control loop and just use the force sensor to measure the target pose or to predict the desired trajectory. In combination with a compliant sensor we introduce an inherently stable framework of force control which almost inhibits all control errors. After an unexpected impact the force error is reduced independently from the sensor's bandwidth or delays in signal processing. Thus the (inevitable) impact force is more significant than the measured force control errors. The special case of a sensor that is mounted far away from a vertex-face contact is discussed, too.

This paper presents a high fidelity force feedback teleoperation control for surgical applications. Advanced control methods, such as flexible joint tracking control and passivity observation, are introduced in the direct force reflecting control architecture. A full state feedback controller of the flexible joint slave robot controls the motor position, velocity, the joint torque, and the torque derivative. The pose of the haptic device and the first three derivatives are observed to generate reference states for the robot control using the robot's inverse dynamics model. Interaction forces of the slave and the environment are measured with a force/torque sensor and directly sent back to the master device. Stability is guaranteed with a passivity observer that monitors the energy in the teleoperation system online and disconnects master and slave if the system operates beyond its stable region. The proposed control architecture is implemented with the sigma.7 haptic device and the MIRO robot. It is experimentally shown, that appropriately considering elasticities with full state reference and control of the slave, increases the dynamic range of the system enabling transparent and stable interaction with hard and soft environments.

A silicon based 3D structure is intended to be used as a sensorgrid for robots, like an "artificial skin". Aim is to simulate the tactile sense of a human skin on a robot. To achieve an optimal sensor geometry, various test are carried out. Part of the test series is a structural simulation of the sensor with ANSYS®. In this document, the results of different structural simulations like • pure displacement with three different electrode geometries, • deformation of a Taxel with Bumper under external force, • deformation of a Taxel without Bumper under external force will be presented.

The WakeScene-D software package (Wake Vortex Scenarios Simulation Package for Departure) has been developed for comprehensive airspace simulations of take-off and departure. WakeScene-D consists of modules that model traffic mix, aircraft trajectories, meteorological conditions, wake vortex evolution, and potential hazard area. The software package estimates the probability to encounter wake vortices in different traffic and crosswind scenarios using Monte Carlo simulation in a domain ranging from the runway to an altitude of 3000 ft above ground. A comparison to measured vortex tracks of about 10,000 departures from runway 25R of Frankfurt airport indicates good agreement of global wake vortex transport characteristics in ground proximity. The standard departure situation employing a two-minute aircraft separation is compared to scenarios with reduced departure separations and various crosswind conditions. Comprehensive sensitivity analyses have been conducted which are briefly recapitulated. Effects related to departure route combinations and wind direction sectors are reported in more detail. Finally, an advanced scenario with an asymmetric crosswind criterion is introduced.

Robot viewers are an important tool for robot developers, programmers and users. This article presents interactive visual features that can be used for robot viewers, including rotating arrows for torque controlled serial robots and special positioned textfields for numerically displaying joint parameters. The presented features support intuitive interaction modes such that the displayed content can be switched or their visibility can be toggled. With these features the DLR SeRo-Viewer has been developed, which aims at minimizing the efforts for integrating new robots in the visualization system, and at the same time being flexible enough to visualize various robotic systems. The SeRo-Viewer has already been successfully applied on several robotic systems.

Multi-fingered robot grasping is a challenging problem that is difficult to tackle using hand-coded programs. In this paper we present an imitation learning approach for learning and generalizing grasping skills based on human demonstrations. To this end, we split the task of synthesizing a grasping motion into three parts: (1) learning efficient grasp representations from human demonstrations, (2) warping contact points onto new objects, and (3) optimizing and executing the reach-and-grasp movements. We learn low-dimensional latent grasp spaces for different grasp types, which form the basis for a novel extension to dynamic motor primitives. These latent-space dynamic motor primitives are used to synthesize entire reach-and-grasp movements. We evaluated our method on a real humanoid robot. The results of the experiment demonstrate the robustness and versatility of our approach.

Medical ultrasound imaging is a well-known technique to gather live views of the interior of the human body. It is totally safe, it provides high spatial and temporal resolution, and it is nowadays available at any hospital. This suggests that it could be used as a human-computer interface. In this paper, we use ultrasound images of the human forearm to predict the finger positions, including thumb adduction and thumb rotation. Our experimental results show that there is a clear linear relationship between the features we extract from the images, and finger positions, expressed as angles at the metacarpo-phalangeal joints. The method is uniformly valid for all subjects considered. The unavoidable movements of the ultrasound probe with respect to the skin and of the skin with respect to the inner musculoskeletal structure are compensated for using the optical flow. Typical applications of this system range from teleoperated fine manipulation to finger stiffness estimation to ergonomy. If successfully applied to transradial amputees, it could be also used to reconstruct the imaginary limb, paving the way to, e.g., fine control of hand prostheses, treatment of neuropathic/phantom limb pain and visualization of the imaginary limb as a tool for the neuroscientist.

Surface electromyography (sEMG) of the forearm is an active research topic since the 1990s in the rehabilitation robotics / machine learning community, as it can be used to predict the hand posture and overall grip force. We hereby advance the state of the art by describing a multi-subject experiment in which sEMG is successfully used to predict simultaneous forces applied by a human subject at the fingertips, that is, when six voluntary muscle contractions (VMCs) are elicited (flexion of the little, ring, middle and index fingers, thumb rotation and thumb adduction). Using a multi-sensor setup sEMG activity of the forearm of a human subject and the forces exerted at the fingertips are measured; a Support Vector Machine is then used to associate sEMG signals and forces. Our results clearly show that sEMG can be used to predict the required forces with an error as small as 1.5\% of the sensor range. Targeted positioning of the electrodes is not required. The prediction is uniformly accurate across all VMCs and all 12 subjects considered, and it is robust against subsampling. This result goes in the direction of enabling natural force / impedance control of a highly dexterous prosthetic hand over a continuous, infinite manifold of force configurations, rather than using posture classification like in the traditional approach.

Die minimal invasive, robotergestützte Chirurgie (MIRC) ist gekennzeichnet durch eine vollständige mechanische Entkopplung von Chirurg und Patient. Die Beurteilung, inwieweit eine Gewebestruktur von Blutgefäßen durchzogen ist, die bei Verletzung zu schwer kontrollierbaren Blutungen führen können, ist schwierig. In der offenen Chirurgie werden nicht sichtbare Blutgefäße im Gewebeverbund mittels Tasten nach Pulsationen detektiert. Dieses sicherheitsrelevante und übliche Vorgehen ist mit der klassischen MIRC-Methodik prinzipbedingt kaum möglich. Mit dem hier vorgestellten unidirektionalen, Ultraschall-Doppler-basierten System können verdeckte, oberflächliche Gefäße mit beliebigem physiologischem Verlauf erkannt werden. Die Rückkopplung an den Chirurgien erfolgt bisher akustisch und/oder kinästhetisch. Mit vertretbarem technischem Aufwand lässt sich damit die intuitive Rückkopplung integrieren. Erste Versuche am Phantom und erste Bewertungen durch Chirurgen zeigen ermutigende Ergebnisse.

The paper presents a new energy shaping control design for a class of underactuated Euler-Lagrange systems. Flexible joint robots, Series Elastic Actuators, and Variable Impedance Actuated Robots Albu-Schaffer et al. [2008] belong for example to this class. First, classical PD control with feed-forward compensation is revisited and a novel, straight-forward and general formulation for the stability analysis is given. Lower bound conditions for the gains of this controller motivate the introduction of the new approach, which generalizes results from Albu-Schaffer et al. [2007], Ch. Ott et al. [2008]. For shaping the potential energy, feedback variables based on the collocated states are introduced, which are statically equivalent to the noncollocated state variables. In this way the passivity is ensured while exactly satisfying steady state requirements formulated in terms of the noncollocated states (such as desired equilibrium configuration and desired stiffness). Using the passivity property, a Lyapunov based analysis can be easily carried out for arbitrarily low feedback gains. The controller is augmented by noncollocated feedback to shape the kinetic energy. Experimental results for a Variable Stiffness Robot Grebenstein et al. [2011] validate the proposed controller.

Complex manipulation tasks require an accurate interplay of actuation and sensing. This accuracy can only be achieved by calibrating the relevant components beforehand. Typically calibration procedures are time-consuming and often include subsequent calibration steps, involve multiple people and require external tools. In this paper we alleviate these issues by auto-calibrating the different sensors of DLR's humanoid Rollin' Justin in a single, completely automatic and self-contained procedure, i.e. without calibration plate. By observing a single point feature on each wrist while moving the robot's head, the stereo cameras' intrinsic and extrinsic parameters are calibrated together with the arm joint elasticities and joint angle offsets. Additionally, we use the head motion to calibrate an Inertial Measurement Unit (IMU) extrinsically. Parameters are obtained by formulating the calibration problem as a batch-optimization problem that estimates all parameters jointly. A rough initial guess, as is, e.g., available when re-calibrating, is needed for the estimation and to facilitate marker detection. The procedure is validated on real hardware and reduces the effort considerably allowing rapid (5 min movement time), automatic, and accurate calibration by simply “pushing a button”.

Robotic systems can benefit from the introduction of properly chosen joint elasticity. Besides their robustness against rigid impact, the energy saving capabilities may increase the system dynamics. In this paper, a method applicable for robots with serial elastic joints is presented, which embodies a desired oscillatory behavior into the hardware and thereby leads to improved performance. This is achieved by shaping the flexible joint robot as a linear one-mode system and embodying the natural frequency of the real intrinsic behavior. An algorithm is presented for shaping the one-mode property and exciting the system via a negative definite damping term in a decoupled coordinate space. The output of the approach is a dynamic trajectory resulting in a coordinated link motion and synchronized transfer of kinetic and potential energy. Furthermore, the dynamic trajectory is commanded to the real robot via a motor PD controller, where asymptotic stability for both subsystems—i.e. the trajectory generator and the controlled robot—is proven. The method is validated on a two-link serial elastic actuated robot. Both, simulation and experiment confirm the eigenmode embodiment, energy efficiency by velocity enlargement between motor and link side motion, and synchronized joint motion.

The goal of this paper is to generate and stabilize a periodic walking motion for a five degrees of freedom planar robot. First of all we will consider a biped version of the spring loaded inverted pendulum (SLIP), which shows open loop stable behavior. Then we will control the robot behavior as close as possible to the simple model. In this way we take advantage of the open-loop stability of the walking pattern related to the SLIP, and additional control actions are used to increase the robustness of the system and reject external disturbances. To this end an upper level controller will deal with the stabilization of the SLIP model, while a lower level controller will map the simple virtual model onto the real robot dynamics. Two different approaches are implemented for the lower level: in the first one, we aim at exactly reproducing the same acceleration that a SLIP would have when put in the same condition, while in the second one, we aim at a simpler control law without exactly reproducing the aforementioned acceleration. The latter case is equivalent to considering a SLIP with additional external disturbances, which have to be handled by the upper level controller. Both approaches can successfully reproduce a periodic walking pattern for the robot.

The use of legs for locomotion through rough terrain promises superior performance in comparison to wheeled vehicles. Nevertheless, most of today's legged machines lack a thorough design that incorporates spring elements in order to achieve elastic behavior. To build a robot which is able to walk and run smoothly, even on rough terrain, new biologically inspired leg concepts need to be developed. Those new legs should have the capability to absorb impacts, to store energy within their elastic elements and to change their stiffness, but to some degree should still allow a dexterous foot placement. Exploiting the benefits of passive compliance is the incentive that directs the research concerning the implementation of elastic systems to replace motors and gears within distinct joints. One of DLR's research goals is to show, using simulation studies, that an appropriately designed self-stabilizing structure can ease the contral and improve the performance of running robots. This research will result in a deeper understanding of elastic multi-Iegged robots and will guide further experimental and analytical research.

In this paper we review our work on safe acting and manipulation in human environments. In order for a robot to be able to safely interact with its environment it is primary to be able to react to unforeseen events in real-time on basically all levels of abstraction. Having this goal in mind, our contributions reach from fundamental understanding of human injury due to robot-human collisions as the underlying metric for “safe” behavior, various interaction control schemes that ground on the basic components impedance control and collision behavior, to real-time motion planning and behavior based control as an interface level for task planning. A significant amount of this work has found found its way into international standardization committees, products, and was applied in numerous real-world applications.