Modeling and Control for a Class of Tendon-Driven Continuum Mechanisms

This thesis contributes to the emerging field of soft material robots and treats modeling, state estimation and control for a special class of continuum mechanisms. The overall outcome of is a novel treatment of a continuum in robotics research. At first a description of the overall system as a tendon-driven multi-body system modeled by a nonlinear rigid-body dynamics is proposed. In combination with the introduced real-time pose and velocity estimation, nonlinear model-based control in real-time is possible. Furthermore, the structural properties of the model allow employing modern control methods for underactuated mechanical systems which are adapted to provide set point control for the upper platform. The developed methods in modeling, state estimation and control presented in this work are experimentally validated on a humanoid robot. Due to their promising results, this thesis lays the foundation for the use of tendon-driven continuum mechanisms as generic joint modules for modular robotic systems which may mark the beginning of a new generation of light-weight robots

Formation of nitrous oxide over Pt-Pd oxidation catalysts: Secondary emissions by interaction of hydrocarbons and nitric oxide

The interaction of hydrocarbons (HC) and nitric oxide (NO) over noble metal catalysts for exhaust gas after-treatment of lean-operated combustion engines can lead to secondary emissions, namely the formation of nitrous oxide (N$_2$O), which is a strong greenhouse gas calling for N$_2$O reduction concepts. By means of a series of light-off tests over state-of-the-art Pt-Pd oxidation catalysts, this study identifies the most critical catalyst operation regimes that should be avoided in order to minimize N$_2$O levels. Especially unsaturated HCs react with NO to form significant amounts of N$_2$O between 150 °C and 350 °C; an increasing HC/NOx ratio generally promotes N$_2$O formation, whereas the NO oxidation reaction is increasingly inhibited. Since low space velocities and fast catalyst heating allow for minimizing N$_2$O levels, active heating of catalytic converters during cold start and phases of low exhaust gas temperatures may efficiently reduce the formation of N$_2$O in real-world applications

Open Source Tendon-driven Continuum Mechanism: A Platform for Research in Soft Robotics

This paper introduces a tendon-driven continuum mechanism platform for research on design, modeling, state estimation, and control of this challenging robotic component envisioned as highly versatile and mechanically robust joint for future robotic systems. To propel the corresponding research areas, a common platform is presented for benchmarking and transferability of results, approaches, and designs among different research groups. The proposed mechanical design including all components is open source, whereas electronics and actuation are off-the-shelf. Research groups are enabled to build up their own system as all relevant CAD-files and assembly instructions are made accessible through GitHub. With that, a fundamental goal in research is achieved and will push continuum joints towards real application scenarios for future soft robots

Fault-Tolerant Six-DoF Pose Estimation for Tendon-Driven Continuum Mechanisms

We propose a fault-tolerant estimation technique for the six-DoF pose of a tendon-driven continuum mechanisms using machine learning. In contrast to previous estimation techniques, no deformation model is required, and the pose prediction is rather performed with polynomial regression. As only a few datapoints are required for the regression, several estimators are trained with structured occlusions of the available sensor information, and clustered into ensembles based on the available sensors. By computing the variance of one ensemble, the uncertainty in the prediction is monitored and, if the variance is above a threshold, sensor loss is detected and handled. Experiments on the humanoid neck of the DLR robot DAVID, demonstrate that the accuracy of the predicted pose is significantly improved, and a reliable prediction can still be performed using only 3 out of 8 sensors

A Robotic Torso Joint With Adjustable Linear Spring Mechanism for Natural Dynamic Motions in a Differential-Elastic Arrangement

To be operated in unknown or complex environments, modern robots have to fulfill various challenging criteria. Among them, one finds requirements such as a high level of robustness to withstand impacts and the capabilities to physically interact in a safe manner. One way to achieve that is to integrate variable-stiffness actuators into the systems, enabling compliant behavior through the elastic components and providing the additional adaptability of the impedance. Here, we introduce a novel adjustable linear stiffness joint mounted in a differential-elastic arrangement. The mechanism is integrated into the anthropomorphic upper body of the DLR David robot and responsible for the spinal rotation. Consequently, the actuator is crucial for the overall workspace of the robot and the realization of energy-efficient natural motions such as in dynamic running. The proposed hardware setup is experimentally validated in terms of the linearity in the spring characteristics, intrinsic damping, the excitation of resonance frequencies, and the ability to alter these resonance frequencies through stiffness adaptation during dynamic motions

A Provably Stable Iterative Learning Controller for Continuum Soft Robots

Fully exploiting soft robots' capabilities requires devising strategies that can accurately control their movements with the limited amount of control sources available. This task is challenging for reasons including the hard-to-model dynamics, the system's underactuation, and the need of using a prominent feedforward control action to preserve the soft and safe robot behavior. To tackle this challenge, this letter proposes a purely feedforward iterative learning control algorithm that refines the torque action by leveraging both the knowledge of the model and data obtained from past experience. After presenting a 3D polynomial description of soft robots, we study their intrinsic properties, e.g., input-to-state stability, and we prove the convergence of the controller coping with locally Lipschitz nonlinearities. Finally, we validate the proposed approach through simulations and experiments involving multiple systems, trajectories, and in the case of external disturbances and model mismatches

Characterization of the MMX Rover Locomotion Flight Model for Check-Out and Parameterization

IDEFIX is a four-wheeled 25kg rover that is jointly developed and built by the French Centre National d'Etudes Spatiales (CNES) and the German Aerospace Center (DLR). It will be brought to the Martian Moon Phobos by the Japan Aerospace Exploration Agency (JAXA) as part of the Martian Moons eXploration (MMX) mission in 2027. IDEFIX's objectives are to scout the surface, demonstrate driving in milligravity and perform scientific measurements. To upright after landing on the surface, drive and align the rover to the sun, each wheel is mounted on a leg, which can be rotated full 360° in its respective shoulder joint. In previous publications, the development, flight design and qualification of the locomotion subsystem were presented. During the cruise phase there will be several health checks and - once landed on Phobos - the locomotion will be checkedout. To be able to analyze the health state quantitatively and parameterize the system properly, a good characterization of the system is important. The foundation of this characterization are tests and health-checks on the flight model (FM), as well as performance test results on the qualification model (QM). A selection of the post-processing and analysis of this measured data, that was done for the characterization of the Loco FM, is presented in this paper

Exploring the oxidation behavior of undiluted and diluted iron particles for energy storage: Mössbauer spectroscopic analysis and kinetic modeling

Iron is an abundant and non-toxic element that holds great potential as energy carrier for large-scale and long-term energy storage. While from a general viewpoint iron oxidation is well-known, the detailed kinetics of oxidation for micrometer sized particles are missing, but required to enable large-scale utilization for energy production. In this work, iron particles are subjected to temperature-programmed oxidation. By dilution with boron nitride a sintering of the particles is prevented enabling to follow single particle effects. The mass fractions of iron and its oxides are determined for different oxidation times using Mössbauer spectroscopy. On the basis of the extracted phase compositions obtained at different times and temperatures (600–700 °C), it can be concluded that also for particles the oxidation follows a parabolic rate law. The parabolic rate constants are determined in this transition region. Knowledge of the particle size distribution and its consideration in modeling the oxidation kinetics of iron powder has proven to be crucial

Modellierung eines robotischen Instruments für die minimal invasive Chirurgie

Die Entwicklung von Systemen für die robotergestützte minimal invasive Chirurgie (MIRS) setzt sich zum Ziel, die Fähigkeiten des Chirurgens auszubauen ohne das Wohl des Patienten zu gefährden. Neben einer höheren Anzahl an Freiheitsgraden im Körper des Patienten und kleineren, beweglicheren Instrumenten steht hier ebenfalls die Steigerung des Grades an Telepräsenz im Vordergrund. Das heißt die Übertragungsstrecke zwischen dem Chirurgen und dem ausführenden Roboter am Patienten muss verzögerungsfrei, ohne spürbare Positionierfehler sowie Interaktionskräfte mit dem menschlichen Gewebe sollen rückkoppelbar sein. Am DLR wird ein robotisches Instrument (MICA) entwickelt, welches oben genannte Bedürfnisse mit einem modularen Aufbau zum vielseitigen Einsatz in der MIRS kombiniert. Es besitzt 3 Freiheitsgrade, die über jeweils einen Motor und Seilzüge bewegt werden sowie einen Kraft- Momentensensor an der Instrumentenspitze, der die Interaktionskräfte erfasst. Zur Rückkopplung dieser ist jedoch die Kenntnis aller Störgrößen und verfeinerte Regelungskonzepte oder Kompensationsmethoden notwendig. Zur Auslegung der Regelungskonzepte oder Kompensationsmethoden bedient man sich eines Simulationsmodells, welches in dieser Arbeit hergeleitet wird. Die Parameter für die meist nichtlinearen Störgrößen sowie die dynamischen Parameter der Seile werden dabei im Rahmen dieser Arbeit identifiziert. Für die Identifikationsverfahren werden dabei Fehler abgeschätzt und später bei der Identifikation des realen Systems berücksichtigt. Eine einfache modellbasierte Kompensation des wirkenden Reibmoments im System wurde in dieser Arbeit getestet und führte zu einer Verbesserung der Positioniergenauigkeit um mindestens 25%. Die identifizierten Parameter werden ebenfalls im Vergleich zwischen Simulation und Modell evaluiert. Darüber hinaus wird in dieser Arbeit auch eine Kraft- sowie eine Impedanzregelung der vom Werkzeug entkoppelten Antriebseinheit getestet