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2016


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Inertial Sensor-Based Humanoid Joint State Estimation

Rotella, N., Mason, S., Schaal, S., Righetti, L.

In 2016 IEEE International Conference on Robotics and Automation (ICRA), pages: 1825-1831, IEEE, Stockholm, Sweden, 2016 (inproceedings)

Abstract
This work presents methods for the determination of a humanoid robot's joint velocities and accelerations directly from link-mounted Inertial Measurement Units (IMUs) each containing a three-axis gyroscope and a three-axis accelerometer. No information about the global pose of the floating base or its links is required and precise knowledge of the link IMU poses is not necessary due to presented calibration routines. Additionally, a filter is introduced to fuse gyroscope angular velocities with joint position measurements and compensate the computed joint velocities for time-varying gyroscope biases. The resulting joint velocities are subject to less noise and delay than filtered velocities computed from numerical differentiation of joint potentiometer signals, leading to superior performance in joint feedback control as demonstrated in experiments performed on a SARCOS hydraulic humanoid.

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link (url) DOI [BibTex]

2016


link (url) DOI [BibTex]


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Stepping Stabilization Using a Combination of DCM Tracking and Step Adjustment

Khadiv, M., Kleff, S., Herzog, A., Moosavian, S. A. A., Schaal, S., Righetti, L.

In 2016 4th International Conference on Robotics and Mechatronics (ICROM), pages: 130-135, IEEE, Teheran, Iran, 2016 (inproceedings)

Abstract
In this paper, a method for stabilizing biped robots stepping by a combination of Divergent Component of Motion (DCM) tracking and step adjustment is proposed. In this method, the DCM trajectory is generated, consistent with the predefined footprints. Furthermore, a swing foot trajectory modification strategy is proposed to adapt the landing point, using DCM measurement. In order to apply the generated trajectories to the full robot, a Hierarchical Inverse Dynamics (HID) is employed. The HID enables us to use different combinations of the DCM tracking and step adjustment for stabilizing different biped robots. Simulation experiments on two scenarios for two different simulated robots, one with active ankles and the other with passive ankles, are carried out. Simulation results demonstrate the effectiveness of the proposed method for robots with both active and passive ankles.

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link (url) DOI [BibTex]

link (url) DOI [BibTex]


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Ab initio theory for ultrafast magnetization dynamics with a dynamic band structure

Müller, B. Y., Haag, M., Fähnle, M.

{Journal of Magnetism and Magnetic Materials}, 414, pages: 14-18, North-Holland, Amsterdam, 2016 (article)

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DOI [BibTex]

DOI [BibTex]


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High-resolution analysis of currents at low-angle grain boundaries in YBCO thin films using magnetooptics and magnetic x-ray microscopy

Ruoß, S., Stahl, C., Bayer, J., Schütz, G., Albrecht, J., Laviano, F.

{IEEE Transactions on Applied Superconductivity}, 26(3), IEEE, New York, NY, 2016 (article)

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DOI [BibTex]

DOI [BibTex]


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Three-dimensional character of the magnetization dynamics in magnetic vortex structures: Hybridization of flexure gyromodes with spin waves

Noske, M., Stoll, H., Fähnle, M., Gangwar, A., Woltersdorf, G., Slavin, A., Weigand, M., Dieterle, G., Förster, J., Back, C. H., Schütz, G.

{Physical Review Letters}, 117(3), American Physical Society, Woodbury, N.Y., 2016 (article)

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DOI [BibTex]

DOI [BibTex]


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Coercivity scaling in antidot lattices in Fe, Ni, and NiFe thin films

Gräfe, J., Schütz, G., Goering, E. J.

{Journal of Magnetism and Magnetic Materials}, 419, pages: 517-520, North-Holland, Amsterdam, 2016 (article)

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DOI Project Page [BibTex]

DOI Project Page [BibTex]


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Nanostructured materials for solid-state hydrogen storage: A review of the achievement of COST Action MP1103

Callini, E., Aguey-Zinsou, K., Ahuja, R., Ares, J. R., Bals, S., Biliskov, N., Chakraborty, S., Charalambopoulou, G., Chaudhary, A., Cuevas, F., Dam, B., de Jongh, P., Dornheim, M., Filinchuk, Y., Grbovic-Novakovic, J., Hirscher, M., Jensen, T. R., Jensen, P. B., Novakovic, N., Lai, Q., Leardini, F., Gattia, D. M., Pasquini, L., Steriotis, T., Turner, S., Vegge, T., Züttel, A., Montone, A.

{International Journal of Hydrogen Energy}, 41(32):14404-14428, Elsevier, Amsterdam, 2016 (article)

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DOI [BibTex]

DOI [BibTex]


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Magnetic X-ray microscopy at low temperatures - Visualization of flux distributions in superconductors

Stahl, C., Ruoß, S., Weigand, M., Bechtel, M., Schütz, G., Albrecht, J.

{AIP Conference Proceedings}, 1696, AIP Publishing, Melville, NY, 2016 (article)

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DOI [BibTex]

DOI [BibTex]


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Enhanced non-adiabaticity in vortex cores due to the emergent Hall effect

Bisig, A., Akosa, C. A., Moon, J., Rhensius, J., Moutafis, C., von Bieren, A., Heidler, J., Kiliani, G., Kammerer, M., Curcic, M., Weigand, M., Tyliszczak, T., Van Waeyenberge, B., Stoll, H., Schütz, G., Lee, K., Manchon, A., Kläui, M.

{Physical Review Letters}, 117(27), American Physical Society, Woodbury, N.Y., 2016 (article)

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DOI [BibTex]

DOI [BibTex]


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Quantitative magneto-optical analysis of the role of finite temperatures on the critical state in YBCO thin films

Albrecht, J., Brück, S., Stahl, C., Ruoß, S.

{Superconductor Science and Technology}, 29(11), IOP Pub., Bristol, 2016 (article)

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DOI [BibTex]

DOI [BibTex]


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Structured contact force optimization for kino-dynamic motion generation

Herzog, A., Schaal, S., Righetti, L.

In 2016 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), pages: 2703-2710, IEEE, Daejeon, South Korea, 2016 (inproceedings)

Abstract
Optimal control approaches in combination with trajectory optimization have recently proven to be a promising control strategy for legged robots. Computationally efficient and robust algorithms were derived using simplified models of the contact interaction between robot and environment such as the linear inverted pendulum model (LIPM). However, as humanoid robots enter more complex environments, less restrictive models become increasingly important. As we leave the regime of linear models, we need to build dedicated solvers that can compute interaction forces together with consistent kinematic plans for the whole-body. In this paper, we address the problem of planning robot motion and interaction forces for legged robots given predefined contact surfaces. The motion generation process is decomposed into two alternating parts computing force and motion plans in coherence. We focus on the properties of the momentum computation leading to sparse optimal control formulations to be exploited by a dedicated solver. In our experiments, we demonstrate that our motion generation algorithm computes consistent contact forces and joint trajectories for our humanoid robot. We also demonstrate the favorable time complexity due to our formulation and composition of the momentum equations.

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link (url) DOI [BibTex]

link (url) DOI [BibTex]


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Balancing and Walking Using Full Dynamics LQR Control With Contact Constraints

Mason, S., Rotella, N., Schaal, S., Righetti, L.

In 2016 IEEE-RAS 16th International Conference on Humanoid Robots (Humanoids), pages: 63-68, IEEE, Cancun, Mexico, 2016 (inproceedings)

Abstract
Torque control algorithms which consider robot dynamics and contact constraints are important for creating dynamic behaviors for humanoids. As computational power increases, algorithms tend to also increase in complexity. However, it is not clear how much complexity is really required to create controllers which exhibit good performance. In this paper, we study the capabilities of a simple approach based on contact consistent LQR controllers designed around key poses to control various tasks on a humanoid robot. We present extensive experimental results on a hydraulic, torque controlled humanoid performing balancing and stepping tasks. This feedback control approach captures the necessary synergies between the DoFs of the robot to guarantee good control performance. We show that for the considered tasks, it is only necessary to re-linearize the dynamics of the robot at different contact configurations and that increasing the number of LQR controllers along desired trajectories does not improve performance. Our result suggest that very simple controllers can yield good performance competitive with current state of the art, but more complex, optimization-based whole-body controllers. A video of the experiments can be found at https://youtu.be/5T08CNKV1hw.

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link (url) DOI [BibTex]

link (url) DOI [BibTex]


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Statische und dynamische Magnetisierungseigenschaften nanoskaliger Überstrukturen

Gräfe, J.

Universität Stuttgart, Stuttgart (und Cuvillier Verlag, Göttingen), 2016 (phdthesis)

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[BibTex]

[BibTex]


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Gepinnte Bahnmomente in magnetischen Heterostrukturen

Audehm, P.

Universität Stuttgart, Stuttgart (und Cuvillier Verlag, Göttingen), 2016 (phdthesis)

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[BibTex]

[BibTex]


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Collective modes in three-dimensional magnonic vortex crystals

Hänze, M., Adolff, C. F., Schulte, B., Möller, J., Weigand, M., Meier, G.

{Scientific Reports}, 6, Nature Publishing Group, London, UK, 2016 (article)

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DOI [BibTex]

DOI [BibTex]


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Spin wave mediated unidirectional vortex core reversal by two orthogonal monopolar field pulses: The essential role of three-dimensional magnetization dynamics

Noske, M., Stoll, H., Fähnle, M., Gangwar, A., Woltersdorf, G., Slavin, A., Weigand, M., Dieterle, G., Förster, J., Back, C. H., Schütz, G.

{Journal of Applied Physics}, 119(17), AIP Publishing, New York, NY, 2016 (article)

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DOI [BibTex]

DOI [BibTex]


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Magnetic vortex cores as tunable spin-wave emitters

Wintz, S., Tiberkevich, V., Weigand, M., Raabe, J., Lindner, J., Erbe, A., Slavin, A., Fassbender, J.

{Nature Nanotechnology}, 11(11):948-953, Nature Publishing Group, London, 2016 (article)

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DOI [BibTex]

DOI [BibTex]


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The usable capacity of porous materials for hydrogen storage

Schlichtenmayer, M., Hirscher, M.

{Applied Physics A}, 122(4), Springer-Verlag Heidelberg, Heidelberg, 2016 (article)

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DOI [BibTex]

DOI [BibTex]


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Ferromagnetic behaviour of ZnO: the role of grain boundaries

Straumal, B. B., Protasova, S. G., Mazilkin, A. A., Goering, E., Schütz, G., Straumal, P. B., Baretzky, B.

{Beilstein Journal of Nanotechnology}, 7, pages: 1936-1947, Beilstein-Institut, Frankfurt am Main, 2016 (article)

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DOI [BibTex]

DOI [BibTex]


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Localized domain wall nucleation dynamics in asymmetric ferromagnetic rings revealed by direct time-resolved magnetic imaging

Richter, K., Krone, A., Mawass, M., Krüger, B., Weigand, M., Stoll, H., Schütz, G., Kläui, M.

{Physical Review B}, 94(2), American Physical Society, Woodbury, NY, 2016 (article)

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DOI [BibTex]

DOI [BibTex]


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Observation of room-temperature magnetic skyrmions and their current-driven dynamics in ultrathin metallic ferromagnets

Woo, S., Litzius, K., Krüger, B., Im, M., Caretta, L., Richter, K., Mann, M., Krone, A., Reeve, R. M., Weigand, M., Agrawal, P., Lemesh, I., Mawass, M., Fischer, P., Kläui, M., Beach, G. S. D.

{Nature Materials}, 15(5):501-506, Nature Pub. Group, London, UK, 2016 (article)

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DOI [BibTex]

DOI [BibTex]


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Step Timing Adjustement: a Step toward Generating Robust Gaits

Khadiv, M., Herzog, A., Moosavian, S. A. A., Righetti, L.

In 2016 IEEE-RAS 16th International Conference on Humanoid Robots (Humanoids), pages: 35-42, IEEE, Cancun, Mexico, 2016 (inproceedings)

Abstract
Step adjustment for humanoid robots has been shown to improve robustness in gaits. However, step duration adaptation is often neglected in control strategies. In this paper, we propose an approach that combines both step location and timing adjustment for generating robust gaits. In this approach, step location and step timing are decided, based on feedback from the current state of the robot. The proposed approach is comprised of two stages. In the first stage, the nominal step location and step duration for the next step or a previewed number of steps are specified. In this stage which is done at the start of each step, the main goal is to specify the best step length and step duration for a desired walking speed. The second stage deals with finding the best landing point and landing time of the swing foot at each control cycle. In this stage, stability of the gaits is preserved by specifying a desired offset between the swing foot landing point and the Divergent Component of Motion (DCM) at the end of current step. After specifying the landing point of the swing foot at a desired time, the swing foot trajectory is regenerated at each control cycle to realize desired landing properties. Simulation on different scenarios shows the robustness of the generated gaits from our proposed approach compared to the case where no timing adjustment is employed.

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link (url) DOI [BibTex]

link (url) DOI [BibTex]


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Austauschgekoppelte Moden in magnetischen Vortexstrukturen

Dieterle, G.

Universität Stuttgart, Stuttgart, 2016 (phdthesis)

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[BibTex]

[BibTex]


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Density matrix calculations for the ultrafast demagnetization after femtosecond laser pulses

Weng, Weikai

Universität Stuttgart, Stuttgart, 2016 (mastersthesis)

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[BibTex]

[BibTex]


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Outlook and challenges for hydrogen storage in nanoporous materials

Broom, D. P., Webb, C. J., Hurst, K. E., Parilla, P. A., Gennett, T., Brown, C. M., Zacharia, R., Tylianakis, E., Klontzas, E., Froudakis, G. E., Steriotis, T. A., Trikalitis, P. N., Anton, D. L., Hardy, B., Tamburello, D., Corgnale, C., van Hassel, B. A., Cossement, D., Chahine, R., Hirscher, M.

{Applied Physics A}, 122(3), Springer-Verlag Heidelberg, Heidelberg, 2016 (article)

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DOI [BibTex]

DOI [BibTex]


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Quantum sieving for separation of hydrogen isotopes using MOFs

Oh, H., Hirscher, M.

{European Journal of Inorganic Chemistry}, 2016(27):4278-4289, Wiley-VCH, Weinheim, Germany, 2016 (article)

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DOI [BibTex]

DOI [BibTex]


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Direct patterning of vortex generators on a fiber tip using a focused ion beam

Vayalamkuzhi, P., Bhattacharya, S., Eigenthaler, U., Keskinbora, K., Salman, C. T., Hirscher, M., Spatz, J. P., Viswanathan, N. K.

{Optics Letters}, 41(10):2133-2136, Optical Society of America, Washington, 2016 (article)

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DOI [BibTex]

DOI [BibTex]


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Two-body problem of core-region coupled magnetic vortex stacks

Hänze, M., Adolff, C. F., Velten, S., Weigand, M., Meier, G.

{Physical Review B}, 93(5), American Physical Society, Woodbury, NY, 2016 (article)

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DOI [BibTex]

DOI [BibTex]


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Irreproducibility in hydrogen storage material research

Broom, D. P., Hirscher, M.

{Energy \& Environmental Science}, 9(11):3368-3380, Royal Society of Chemistry, Cambridge, UK, 2016 (article)

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DOI [BibTex]

DOI [BibTex]


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Effect of surface configurations on the room-temperature magnetism of pure ZnO

Chen, Y., Wang, Z., Leineweber, A., Baier, J., Tietze, T., Phillipp, F., Schütz, G., Goering, E.

{Journal of Materials Chemistry C}, 4(19):4166-4175, Royal Society of Chemistry, London, UK, 2016 (article)

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DOI [BibTex]

DOI [BibTex]


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On the synthesis and microstructure analysis of high performance MnBi

Chen, Y., Sawatzki, S., Ener, S., Sepehri-Amin, H., Leineweber, A., Gregori, G., Qu, F., Muralidhar, S., Ohkubo, T., Hono, K., Gutfleisch, O., Kronmüller, H., Schütz, G., Goering, E.

{AIP Advances}, 6(12), 2016 (article)

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DOI [BibTex]

DOI [BibTex]


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The role of individual defects on the magnetic screening of HTSC films

Ruoß, S., Stahl, C., Weigand, M., Zahn, P., Bayer, J., Schütz, G., Albrecht, J.

{New Journal of Physics}, 18(10), IOP Publishing, Bristol, 2016 (article)

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DOI [BibTex]

DOI [BibTex]


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Magnetic switching of nanoscale antidot lattices

Wiedwald, U., Gräfe, J., Lebecki, K. M., Skripnik, M., Haering, F., Schütz, G., Ziemann, P., Goering, E., Nowak, U.

{Beilstein Journal of Nanotechnology}, 7, pages: 733-750, Beilstein-Institut, Frankfurt am Main, 2016 (article)

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DOI Project Page [BibTex]

DOI Project Page [BibTex]


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Hydrogen-based energy storage (IEA-HIA Task 32)

Buckley, C. E., Chen, P., van Hassel, B. A., Hirscher, M.

{Applied Physics A}, 122(2), Springer-Verlag Heidelberg, Heidelberg, 2016 (article)

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DOI [BibTex]

DOI [BibTex]


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Local domain-wall velocity engineering via tailored potential landscapes in ferromagnetic rings

Richter, K., Krone, A., Mawass, M., Krüger, B., Weigand, M., Stoll, H., Schütz, G., Kläui, M.

{Physical Review Applied}, 5(2), American Physical Society, College Park, Md. [u.a.], 2016 (article)

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DOI [BibTex]

DOI [BibTex]


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Geometric control of the magnetization reversal in antidot lattices with perpendicular magnetic anisotropy

Gräfe, J., Weigand, M., Träger, N., Schütz, G., Goering, E. J., Skripnik, M., Nowak, U., Haering, F., Ziemann, P., Wiedwald, U.

{Physical Review B}, 93(10), American Physical Society, Woodbury, NY, 2016 (article)

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DOI Project Page Project Page [BibTex]

DOI Project Page Project Page [BibTex]


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Growth and characterizationof large weak topological insulator Bi2Tel single crystal by Bismuth self-flux method

Ryu, G., Son, K., Schütz, G.

{Journal of Crystal Growth}, 440, pages: 26-30, North-Holland, Amsterdam, 2016 (article)

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DOI [BibTex]

DOI [BibTex]


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Additive interfacial chiral interaction in multilayers for stabilization of small individual skyrmions at room temperature

Moreau-Luchaire, C., Moutafis, C., Reyren, N., Sampaio, J., Vaz, C. A. F., Van Horne, N., Bouzehouane, K., Garcia, K., Deranlot, C., Warnicke, P., Wohlhüter, P., George, J.-M., Weigand, M., Raabe, J., Cros, V., Fert, A.

{Nature Nanotechnology}, 11(5):444-448, Nature Publishing Group, London, 2016 (article)

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DOI [BibTex]

DOI [BibTex]


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Surface defect free growth of a spin dimer TlCuCl3 compound crystals and investigations on its optical and magnetic properties

Ryu, G., Son, K.

{Journal of Solid State Chemistry}, 237, pages: 358-363, Academic Press, Orlando, Fla., 2016 (article)

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DOI [BibTex]

DOI [BibTex]


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Physical and mathematical justification of the numerical Brillouin zone integration of the Boltzmann rate equation by Gaussian smearing

Illg, C., Haag, M., Teeny, N., Wirth, J., Fähnle, M.

{Journal of Theoretical and Applied Physics}, 10(1):1-6, Springer, Berlin, Heidelberg, Tehran, 2016 (article)

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DOI [BibTex]

DOI [BibTex]


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On the Effects of Measurement Uncertainty in Optimal Control of Contact Interactions

Ponton, B., Schaal, S., Righetti, L.

In The 12th International Workshop on the Algorithmic Foundations of Robotics WAFR, Berkeley, USA, 2016 (inproceedings)

Abstract
Stochastic Optimal Control (SOC) typically considers noise only in the process model, i.e. unknown disturbances. However, in many robotic applications involving interaction with the environment, such as locomotion and manipulation, uncertainty also comes from lack of precise knowledge of the world, which is not an actual disturbance. We analyze the effects of also considering noise in the measurement model, by devel- oping a SOC algorithm based on risk-sensitive control, that includes the dynamics of an observer in such a way that the control law explicitly de- pends on the current measurement uncertainty. In simulation results on a simple 2D manipulator, we have observed that measurement uncertainty leads to low impedance behaviors, a result in contrast with the effects of process noise that creates stiff behaviors. This suggests that taking into account measurement uncertainty could be a potentially very interesting way to approach problems involving uncertain contact interactions.

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link (url) [BibTex]

link (url) [BibTex]


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A Convex Model of Momentum Dynamics for Multi-Contact Motion Generation

Ponton, B., Herzog, A., Schaal, S., Righetti, L.

In 2016 IEEE-RAS 16th International Conference on Humanoid Robots Humanoids, pages: 842-849, IEEE, Cancun, Mexico, 2016 (inproceedings)

Abstract
Linear models for control and motion generation of humanoid robots have received significant attention in the past years, not only due to their well known theoretical guarantees, but also because of practical computational advantages. However, to tackle more challenging tasks and scenarios such as locomotion on uneven terrain, a more expressive model is required. In this paper, we are interested in contact interaction-centered motion optimization based on the momentum dynamics model. This model is non-linear and non-convex; however, we find a relaxation of the problem that allows us to formulate it as a single convex quadratically-constrained quadratic program (QCQP) that can be very efficiently optimized and is useful for multi-contact planning. This convex model is then coupled to the optimization of end-effector contact locations using a mixed integer program, which can also be efficiently solved. This becomes relevant e.g. to recover from external pushes, where a predefined stepping plan is likely to fail and an online adaptation of the contact location is needed. The performance of our algorithm is demonstrated in several multi-contact scenarios for a humanoid robot.

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link (url) DOI [BibTex]

link (url) DOI [BibTex]


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Helium und Hydrogen Isotope Adsorption and Separation in Metal-Organic Frameworks

Zaiser, Ingrid

Universität Stuttgart, Stuttgart (und Cuvillier Verlag, Göttingen), 2016 (phdthesis)

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[BibTex]

[BibTex]


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Pinned orbital moments - A new contribution to magnetic anisotropy

Audehm, P., Schmidt, M., Brück, S., Tietze, T., Gräfe, J., Macke, S., Schütz, G., Goering, E.

{Scientific Reports}, 6, Nature Publishing Group, London, UK, 2016 (article)

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DOI [BibTex]

DOI [BibTex]


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Comparative study of ALD SiO2 thin films for optical applications

Pfeiffer, K., Shestaeva, S., Bingel, A., Munzert, P., Ghazaryan, L., van Helvoirt, C., Kessels, W. M. M., Sanli, U. T., Grévent, C., Schütz, G., Putkonen, M., Buchanan, I., Jensen, L., Ristau, D., Tünnermann, A., Szeghalmi, A.

{Optical materials express}, 6(2):660-670, OSA, Washington, DC, 2016 (article)

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DOI [BibTex]

DOI [BibTex]


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Combined first-order reversal curve and x-ray microscopy investigation of magnetization reversal mechanisms in hexagonal antidot lattices

Gräfe, J., Weigand, M., Stahl, C., Träger, N., Kopp, M., Schütz, G., Goering, E. J., Haering, F., Ziemann, P., Wiedwald, U.

{Physical Review B}, 93(1), American Physical Society, Woodbury, NY, 2016 (article)

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DOI Project Page Project Page [BibTex]

DOI Project Page Project Page [BibTex]


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Switching probabilities of magnetic vortex core reversal studied by table top magneto optic Kerr microscopy

Dieterle, G., Gangwar, A., Gräfe, J., Noske, M., Förster, J., Woltersdorf, G., Stoll, H., Back, C. H., Schütz, G.

{Applied Physics Letters}, 108(2), American Institute of Physics, Melville, NY, 2016 (article)

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DOI [BibTex]

DOI [BibTex]


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Ultrafast demagnetization after femtosecond laser pulses: Transfer of angular momentum from the electronic system to magnetoelastic spin-phonon modes

Tsatsoulis, T., Illg, C., Haag, M., Müller, B. Y., Zhang, L., Fähnle, M.

{Physical Review B}, 93(13), American Physical Society, Woodbury, NY, 2016 (article)

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DOI [BibTex]

DOI [BibTex]