Publications | Max Planck Institute for Intelligent Systems

94 results (View BibTeX file of all listed publications)

2009

Magnetic mobile micro-robots

Pawashe, C., Floyd, S., Sitti, M.

7eme Journees Nationales de la Recherche en Robotique, 2009 (article)

2009

pi Pawashe, C., Floyd, S., Sitti, M. Magnetic mobile micro-robots 7eme Journees Nationales de la Recherche en Robotique, 2009 (article)

[BibTex]

Gecko-Inspired Directional and Controllable Adhesion

Murphy, M. P., Aksak, B., Sitti, M.

Small, 5(2):170-175, WILEY-VCH Verlag, 2009 (article)

Project Page [BibTex]

pi Murphy, M. P., Aksak, B., Sitti, M. Gecko-Inspired Directional and Controllable Adhesion Small, 5(2):170-175, WILEY-VCH Verlag, 2009 (article)

Project Page [BibTex]

Multiple magnetic microrobot control using electrostatic anchoring

Pawashe, C., Floyd, S., Sitti, M.

Applied Physics Letters, 94(16):164108, AIP, 2009 (article)

[BibTex]

pi Pawashe, C., Floyd, S., Sitti, M. Multiple magnetic microrobot control using electrostatic anchoring Applied Physics Letters, 94(16):164108, AIP, 2009 (article)

[BibTex]

Characterization of bacterial actuation of micro-objects

Behkam, B., Sitti, M.

In Robotics and Automation, 2009. ICRA’09. IEEE International Conference on, pages: 1022-1027, 2009 (inproceedings)

[BibTex]

pi Behkam, B., Sitti, M. Characterization of bacterial actuation of micro-objects In Robotics and Automation, 2009. ICRA’09. IEEE International Conference on, pages: 1022-1027, 2009 (inproceedings)

[BibTex]

Wet self-cleaning of biologically inspired elastomer mushroom shaped microfibrillar adhesives

Kim, S., Cheung, E., Sitti, M.

Langmuir, 25(13):7196-7199, ACS Publications, 2009 (article)

[BibTex]

pi Kim, S., Cheung, E., Sitti, M. Wet self-cleaning of biologically inspired elastomer mushroom shaped microfibrillar adhesives Langmuir, 25(13):7196-7199, ACS Publications, 2009 (article)

[BibTex]

Compliant footpad design analysis for a bio-inspired quadruped amphibious robot

Park, H. S., Sitti, M.

In Intelligent Robots and Systems, 2009. IROS 2009. IEEE/RSJ International Conference on, pages: 645-651, 2009 (inproceedings)

[BibTex]

pi Park, H. S., Sitti, M. Compliant footpad design analysis for a bio-inspired quadruped amphibious robot In Intelligent Robots and Systems, 2009. IROS 2009. IEEE/RSJ International Conference on, pages: 645-651, 2009 (inproceedings)

[BibTex]

Path integral-based stochastic optimal control for rigid body dynamics

Theodorou, E. A., Buchli, J., Schaal, S.

In Adaptive Dynamic Programming and Reinforcement Learning, 2009. ADPRL ’09. IEEE Symposium on, pages: 219-225, 2009, clmc (inproceedings)

Abstract

Recent advances on path integral stochastic optimal control [1],[2] provide new insights in the optimal control of nonlinear stochastic systems which are linear in the controls, with state independent and time invariant control transition matrix. Under these assumptions, the Hamilton-Jacobi-Bellman (HJB) equation is formulated and linearized with the use of the logarithmic transformation of the optimal value function. The resulting HJB is a linear second order partial differential equation which is solved by an approximation based on the Feynman-Kac formula [3]. In this work we review the theory of path integral control and derive the linearized HJB equation for systems with state dependent control transition matrix. In addition we derive the path integral formulation for the general class of systems with state dimensionality that is higher than the dimensionality of the controls. Furthermore, by means of a modified inverse dynamics controller, we apply path integral stochastic optimal control over the new control space. Simulations illustrate the theoretical results. Future developments and extensions are discussed.

link (url) [BibTex]

am Theodorou, E. A., Buchli, J., Schaal, S. Path integral-based stochastic optimal control for rigid body dynamics In Adaptive Dynamic Programming and Reinforcement Learning, 2009. ADPRL ’09. IEEE Symposium on, pages: 219-225, 2009, clmc (inproceedings)

link (url) [BibTex]

Learning locomotion over rough terrain using terrain templates

Kalakrishnan, M., Buchli, J., Pastor, P., Schaal, S.

In Intelligent Robots and Systems, 2009. IROS 2009. IEEE/RSJ International Conference on, pages: 167-172, 2009, clmc (inproceedings)

Abstract

We address the problem of foothold selection in robotic legged locomotion over very rough terrain. The difficulty of the problem we address here is comparable to that of human rock-climbing, where foot/hand-hold selection is one of the most critical aspects. Previous work in this domain typically involves defining a reward function over footholds as a weighted linear combination of terrain features. However, a significant amount of effort needs to be spent in designing these features in order to model more complex decision functions, and hand-tuning their weights is not a trivial task. We propose the use of terrain templates, which are discretized height maps of the terrain under a foothold on different length scales, as an alternative to manually designed features. We describe an algorithm that can simultaneously learn a small set of templates and a foothold ranking function using these templates, from expert-demonstrated footholds. Using the LittleDog quadruped robot, we experimentally show that the use of terrain templates can produce complex ranking functions with higher performance than standard terrain features, and improved generalization to unseen terrain.

link (url) Project Page [BibTex]

am Kalakrishnan, M., Buchli, J., Pastor, P., Schaal, S. Learning locomotion over rough terrain using terrain templates In Intelligent Robots and Systems, 2009. IROS 2009. IEEE/RSJ International Conference on, pages: 167-172, 2009, clmc (inproceedings)

link (url) Project Page [BibTex]

Teleoperated Three-Dimensional Force Feedback from the Nanoscale with an Atomic Force Microscope

Onal, C. D., Sitti, M.

2009 (article)

[BibTex]

pi Onal, C. D., Sitti, M. Teleoperated Three-Dimensional Force Feedback from the Nanoscale with an Atomic Force Microscope 2009 (article)

[BibTex]

A novel artificial hair receptor based on aligned PVDF micro/nano fibers

Weiting, Liu, Bilsay, Sumer, Cesare, Stefanini, Arianna, Menciassi, Fei, Li, Dajing, Chen, Paolo, Dario, Metin, Sitti, Xin, Fu

In Robotics and Biomimetics, 2008. ROBIO 2008. IEEE International Conference on, pages: 49-54, 2009 (inproceedings)

[BibTex]

pi Weiting, Liu, Bilsay, Sumer, Cesare, Stefanini, Arianna, Menciassi, Fei, Li, Dajing, Chen, Paolo, Dario, Metin, Sitti, Xin, Fu A novel artificial hair receptor based on aligned PVDF micro/nano fibers In Robotics and Biomimetics, 2008. ROBIO 2008. IEEE International Conference on, pages: 49-54, 2009 (inproceedings)

[BibTex]

Robot ceiling climbers harness new tricks

Marks, Paul

New Scientist, 202(2705):18-19, Reed Business Information, 2009 (article)

[BibTex]

pi Marks, Paul Robot ceiling climbers harness new tricks New Scientist, 202(2705):18-19, Reed Business Information, 2009 (article)

[BibTex]

Waalbot: Agile climbing with synthetic fibrillar dry adhesives

Murphy, M. P., Sitti, M.

In Robotics and Automation, 2009. ICRA’09. IEEE International Conference on, pages: 1599-1600, 2009 (inproceedings)

[BibTex]

pi Murphy, M. P., Sitti, M. Waalbot: Agile climbing with synthetic fibrillar dry adhesives In Robotics and Automation, 2009. ICRA’09. IEEE International Conference on, pages: 1599-1600, 2009 (inproceedings)

[BibTex]

Biologically-Inspired Patterned and Coated Adhesives for Medical Devices

Glass, P, Chung, H, Lee, C, Tworkoski, E, Washburn, NR, Sitti, M

Journal of Medical Devices, 3(2):027537, American Society of Mechanical Engineers, 2009 (article)

[BibTex]

pi Glass, P, Chung, H, Lee, C, Tworkoski, E, Washburn, NR, Sitti, M Biologically-Inspired Patterned and Coated Adhesives for Medical Devices Journal of Medical Devices, 3(2):027537, American Society of Mechanical Engineers, 2009 (article)

[BibTex]

Modeling and experimental characterization of an untethered magnetic micro-robot

Pawashe, C., Floyd, S., Sitti, M.

The International Journal of Robotics Research, 28(8):1077-1094, Sage Publications, 2009 (article)

[BibTex]

pi Pawashe, C., Floyd, S., Sitti, M. Modeling and experimental characterization of an untethered magnetic micro-robot The International Journal of Robotics Research, 28(8):1077-1094, Sage Publications, 2009 (article)

[BibTex]

Towards automated nanoassembly with the atomic force microscope: A versatile drift compensation procedure

Krohs, F., Onal, C., Sitti, M., Fatikow, S.

Journal of Dynamic Systems, Measurement, and Control, 131(6):061106, American Society of Mechanical Engineers, 2009 (article)

[BibTex]

pi Krohs, F., Onal, C., Sitti, M., Fatikow, S. Towards automated nanoassembly with the atomic force microscope: A versatile drift compensation procedure Journal of Dynamic Systems, Measurement, and Control, 131(6):061106, American Society of Mechanical Engineers, 2009 (article)

[BibTex]

Valero-Cuevas, F., Hoffmann, H., Kurse, M. U., Kutch, J. J., Theodorou, E. A.

IEEE Reviews in Biomedical Engineering – (All authors have equally contributed), (2):110?135, 2009, clmc (article)

Abstract

Computational models of the neuromuscular system hold the potential to allow us to reach a deeper understanding of neuromuscular function and clinical rehabilitation by complementing experimentation. By serving as a means to distill and explore specific hypotheses, computational models emerge from prior experimental data and motivate future experimental work. Here we review computational tools used to understand neuromuscular function including musculoskeletal modeling, machine learning, control theory, and statistical model analysis. We conclude that these tools, when used in combination, have the potential to further our understanding of neuromuscular function by serving as a rigorous means to test scientific hypotheses in ways that complement and leverage experimental data.

link (url) [BibTex]

am Valero-Cuevas, F., Hoffmann, H., Kurse, M. U., Kutch, J. J., Theodorou, E. A. Computational models for neuromuscular function IEEE Reviews in Biomedical Engineering – (All authors have equally contributed), (2):110?135, 2009, clmc (article)

link (url) [BibTex]

Compact models of motor primitive variations for predictible reaching and obstacle avoidance

Stulp, F., Oztop, E., Pastor, P., Beetz, M., Schaal, S.

In IEEE-RAS International Conference on Humanoid Robots (Humanoids 2009), Paris, Dec.7-10, 2009, clmc (inproceedings)

Abstract

over and over again. This regularity allows humans and robots to reuse existing solutions for known recurring tasks. We expect that reusing a set of standard solutions to solve similar tasks will facilitate the design and on-line adaptation of the control systems of robots operating in human environments. In this paper, we derive a set of standard solutions for reaching behavior from human motion data. We also derive stereotypical reaching trajectories for variations of the task, in which obstacles are present. These stereotypical trajectories are then compactly represented with Dynamic Movement Primitives. On the humanoid robot Sarcos CB, this approach leads to reproducible, predictable, and human-like reaching motions.

link (url) [BibTex]

am Stulp, F., Oztop, E., Pastor, P., Beetz, M., Schaal, S. Compact models of motor primitive variations for predictible reaching and obstacle avoidance In IEEE-RAS International Conference on Humanoid Robots (Humanoids 2009), Paris, Dec.7-10, 2009, clmc (inproceedings)

link (url) [BibTex]

Human optimization strategies under reward feedback

Hoffmann, H., Theodorou, E., Schaal, S.

In Abstracts of Neural Control of Movement Conference (NCM 2009), Waikoloa, Hawaii, 2009, 2009, clmc (inproceedings)

Abstract

Many hypothesis on human movement generation have been cast into an optimization framework, implying that movements are adapted to optimize a single quantity, like, e.g., jerk, end-point variance, or control cost. However, we still do not understand how humans actually learn when given only a cost or reward feedback at the end of a movement. Such a reinforcement learning setting has been extensively explored theoretically in engineering and computer science, but in human movement control, hardly any experiment studied movement learning under reward feedback. We present experiments probing which computational strategies humans use to optimize a movement under a continuous reward function. We present two experimental paradigms. The first paradigm mimics a ball-hitting task. Subjects (n=12) sat in front of a computer screen and moved a stylus on a tablet towards an unknown target. This target was located on a line that the subjects had to cross. During the movement, visual feedback was suppressed. After the movement, a reward was displayed graphically as a colored bar. As reward, we used a Gaussian function of the distance between the target location and the point of line crossing. We chose such a function since in sensorimotor tasks, the cost or loss function that humans seem to represent is close to an inverted Gaussian function (Koerding and Wolpert 2004). The second paradigm mimics pocket billiards. On the same experimental setup as above, the computer screen displayed a pocket (two bars), a white disk, and a green disk. The goal was to hit with the white disk the green disk (as in a billiard collision), such that the green disk moved into the pocket. Subjects (n=8) manipulated with the stylus the white disk to effectively choose start point and movement direction. Reward feedback was implicitly given as hitting or missing the pocket with the green disk. In both paradigms, subjects increased the average reward over trials. The surprising result was that in these experiments, humans seem to prefer a strategy that uses a reward-weighted average over previous movements instead of gradient ascent. The literature on reinforcement learning is dominated by gradient-ascent methods. However, our computer simulations and theoretical analysis revealed that reward-weighted averaging is the more robust choice given the amount of movement variance observed in humans. Apparently, humans choose an optimization strategy that is suitable for their own movement variance.

[BibTex]

am Hoffmann, H., Theodorou, E., Schaal, S. Human optimization strategies under reward feedback In Abstracts of Neural Control of Movement Conference (NCM 2009), Waikoloa, Hawaii, 2009, 2009, clmc (inproceedings)

[BibTex]

Bayesian Methods for Autonomous Learning Systems (Phd Thesis)

Ting, J.

Department of Computer Science, University of Southern California, Los Angeles, CA, 2009, clmc (phdthesis)

PDF [BibTex]

am Ting, J. Bayesian Methods for Autonomous Learning Systems (Phd Thesis) Department of Computer Science, University of Southern California, Los Angeles, CA, 2009, clmc (phdthesis)

PDF [BibTex]

On-line learning and modulation of periodic movements with nonlinear dynamical systems

Gams, A., Ijspeert, A., Schaal, S., Lenarčič, J.

Autonomous Robots, 27(1):3-23, 2009, clmc (article)

Abstract

Abstract The paper presents a two-layered system for (1) learning and encoding a periodic signal without any knowledge on its frequency and waveform, and (2) modulating the learned periodic trajectory in response to external events. The system is used to learn periodic tasks on a humanoid HOAP-2 robot. The first layer of the system is a dynamical system responsible for extracting the fundamental frequency of the input signal, based on adaptive frequency oscillators. The second layer is a dynamical system responsible for learning of the waveform based on a built-in learning algorithm. By combining the two dynamical systems into one system we can rapidly teach new trajectories to robots without any knowledge of the frequency of the demonstration signal. The system extracts and learns only one period of the demonstration signal. Furthermore, the trajectories are robust to perturbations and can be modulated to cope with a dynamic environment. The system is computationally inexpensive, works on-line for any periodic signal, requires no additional signal processing to determine the frequency of the input signal and can be applied in parallel to multiple dimensions. Additionally, it can adapt to changes in frequency and shape, e.g. to non-stationary signals, such as hand-generated signals and human demonstrations.

link (url) [BibTex]

am Gams, A., Ijspeert, A., Schaal, S., Lenarčič, J. On-line learning and modulation of periodic movements with nonlinear dynamical systems Autonomous Robots, 27(1):3-23, 2009, clmc (article)

link (url) [BibTex]

The SL simulation and real-time control software package

Schaal, S.

University of Southern California, Los Angeles, CA, 2009, clmc (techreport)

Abstract

SL was originally developed as a Simulation Laboratory software package to allow creating complex rigid-body dynamics simulations with minimal development times. It was meant to complement a real-time robotics setup such that robot programs could first be debugged in simulation before trying them on the actual robot. For this purpose, the motor control setup of SL was copied from our experience with real-time robot setups with vxWorks (Windriver Systems, Inc.)Ñindeed, more than 90% of the code is identical to the actual robot software, as will be explained later in detail. As a result, SL is divided into three software components: 1) the generic code that is shared by the actual robot and the simulation, 2) the robot specific code, and 3) the simulation specific code. The robot specific code is tailored to the robotic environments that we have experienced over the years, in particular towards VME-based multi-processor real-time operating systems. The simulation specific code has all the components for OpenGL graphics simulations and mimics the robot multi-processor environment in simple C-code. Importantly, SL can be used stand-alone for creating graphics an-imationsÑthe heritage from real-time robotics does not restrict the complexity of possible simulations. This technical report describes SL in detail and can serve as a manual for new users of SL.

link (url) [BibTex]

am Schaal, S. The SL simulation and real-time control software package University of Southern California, Los Angeles, CA, 2009, clmc (techreport)

link (url) [BibTex]

Local dimensionality reduction for non-parametric regression

Hoffman, H., Schaal, S., Vijayakumar, S.

Neural Processing Letters, 2009, clmc (article)

Abstract

Locally-weighted regression is a computationally-efficient technique for non-linear regression. However, for high-dimensional data, this technique becomes numerically brittle and computationally too expensive if many local models need to be maintained simultaneously. Thus, local linear dimensionality reduction combined with locally-weighted regression seems to be a promising solution. In this context, we review linear dimensionality-reduction methods, compare their performance on nonparametric locally-linear regression, and discuss their ability to extend to incremental learning. The considered methods belong to the following three groups: (1) reducing dimensionality only on the input data, (2) modeling the joint input-output data distribution, and (3) optimizing the correlation between projection directions and output data. Group 1 contains principal component regression (PCR); group 2 contains principal component analysis (PCA) in joint input and output space, factor analysis, and probabilistic PCA; and group 3 contains reduced rank regression (RRR) and partial least squares (PLS) regression. Among the tested methods, only group 3 managed to achieve robust performance even for a non-optimal number of components (factors or projection directions). In contrast, group 1 and 2 failed for fewer components since these methods rely on the correct estimate of the true intrinsic dimensionality. In group 3, PLS is the only method for which a computationally-efficient incremental implementation exists. Thus, PLS appears to be ideally suited as a building block for a locally-weighted regressor in which projection directions are incrementally added on the fly.

link (url) [BibTex]

am Hoffman, H., Schaal, S., Vijayakumar, S. Local dimensionality reduction for non-parametric regression Neural Processing Letters, 2009, clmc (article)

link (url) [BibTex]

Enhanced adhesion by gecko-inspired hierarchical fibrillar adhesives

Murphy, M. P., Kim, S., Sitti, M.

ACS applied materials \& interfaces, 1(4):849-855, American Chemical Society, 2009 (article)

Project Page [BibTex]

pi Murphy, M. P., Kim, S., Sitti, M. Enhanced adhesion by gecko-inspired hierarchical fibrillar adhesives ACS applied materials \& interfaces, 1(4):849-855, American Chemical Society, 2009 (article)

Project Page [BibTex]

Miniature devices: Voyage of the microrobots

Sitti, M.

Nature, 458(7242):1121-1122, Nature Publishing Group, 2009 (article)

[BibTex]

pi Sitti, M. Miniature devices: Voyage of the microrobots Nature, 458(7242):1121-1122, Nature Publishing Group, 2009 (article)

[BibTex]

Piezoelectric ultrasonic resonant micromotor with a volume of less than 1 mm 3 for use in medical microbots

Watson, B., Friend, J., Yeo, L., Sitti, M.

In Robotics and Automation, 2009. ICRA’09. IEEE International Conference on, pages: 2225-2230, 2009 (inproceedings)

[BibTex]

pi Watson, B., Friend, J., Yeo, L., Sitti, M. Piezoelectric ultrasonic resonant micromotor with a volume of less than 1 mm 3 for use in medical microbots In Robotics and Automation, 2009. ICRA’09. IEEE International Conference on, pages: 2225-2230, 2009 (inproceedings)

[BibTex]

Dynamic modeling and analysis of pitch motion of a basilisk lizard inspired quadruped robot running on water

Park, H. S., Floyd, S., Sitti, M.

In Robotics and Automation, 2009. ICRA’09. IEEE International Conference on, pages: 2655-2660, 2009 (inproceedings)

[BibTex]

pi Park, H. S., Floyd, S., Sitti, M. Dynamic modeling and analysis of pitch motion of a basilisk lizard inspired quadruped robot running on water In Robotics and Automation, 2009. ICRA’09. IEEE International Conference on, pages: 2655-2660, 2009 (inproceedings)

[BibTex]

Dry spinning based spinneret based tunable engineered parameters (STEP) technique for controlled and aligned deposition of polymeric nanofibers

Nain, A. S., Sitti, M., Jacobson, A., Kowalewski, T., Amon, C.

Macromolecular rapid communications, 30(16):1406-1412, WILEY-VCH Verlag, 2009 (article)

[BibTex]

pi Nain, A. S., Sitti, M., Jacobson, A., Kowalewski, T., Amon, C. Dry spinning based spinneret based tunable engineered parameters (STEP) technique for controlled and aligned deposition of polymeric nanofibers Macromolecular rapid communications, 30(16):1406-1412, WILEY-VCH Verlag, 2009 (article)

[BibTex]

Two-dimensional contact and noncontact micromanipulation in liquid using an untethered mobile magnetic microrobot

Floyd, S., Pawashe, C., Sitti, M.

IEEE Transactions on Robotics, 25(6):1332-1342, IEEE, 2009 (article)

[BibTex]

pi Floyd, S., Pawashe, C., Sitti, M. Two-dimensional contact and noncontact micromanipulation in liquid using an untethered mobile magnetic microrobot IEEE Transactions on Robotics, 25(6):1332-1342, IEEE, 2009 (article)

[BibTex]

The SL simulation and real-time control software package

Schaal, S.

University of Southern California, Los Angeles, CA, 2009, clmc (techreport)

Abstract

SL was originally developed as a Simulation Laboratory software package to allow creating complex rigid-body dynamics simulations with minimal development times. It was meant to complement a real-time robotics setup such that robot programs could first be debugged in simulation before trying them on the actual robot. For this purpose, the motor control setup of SL was copied from our experience with real-time robot setups with vxWorks (Windriver Systems, Inc.)â??indeed, more than 90% of the code is identical to the actual robot software, as will be explained later in detail. As a result, SL is divided into three software components: 1) the generic code that is shared by the actual robot and the simulation, 2) the robot specific code, and 3) the simulation specific code. The robot specific code is tailored to the robotic environments that we have experienced over the years, in particular towards VME-based multi-processor real-time operating systems. The simulation specific code has all the components for OpenGL graphics simulations and mimics the robot multi-processor environment in simple C-code. Importantly, SL can be used stand-alone for creating graphics an-imationsâ??the heritage from real-time robotics does not restrict the complexity of possible simulations. This technical report describes SL in detail and can serve as a manual for new users of SL.

link (url) [BibTex]

am Schaal, S. The SL simulation and real-time control software package University of Southern California, Los Angeles, CA, 2009, clmc (techreport)

link (url) [BibTex]

Learning and generalization of motor skills by learning from demonstration

Pastor, P., Hoffmann, H., Asfour, T., Schaal, S.

In International Conference on Robotics and Automation (ICRA2009), Kobe, Japan, May 12-19, 2009, 2009, clmc (inproceedings)

Abstract

We provide a general approach for learning robotic motor skills from human demonstration. To represent an observed movement, a non-linear differential equation is learned such that it reproduces this movement. Based on this representation, we build a library of movements by labeling each recorded movement according to task and context (e.g., grasping, placing, and releasing). Our differential equation is formulated such that generalization can be achieved simply by adapting a start and a goal parameter in the equation to the desired position values of a movement. For object manipulation, we present how our framework extends to the control of gripper orientation and finger position. The feasibility of our approach is demonstrated in simulation as well as on a real robot. The robot learned a pick-and-place operation and a water-serving task and could generalize these tasks to novel situations.

link (url) [BibTex]

am Pastor, P., Hoffmann, H., Asfour, T., Schaal, S. Learning and generalization of motor skills by learning from demonstration In International Conference on Robotics and Automation (ICRA2009), Kobe, Japan, May 12-19, 2009, 2009, clmc (inproceedings)

link (url) [BibTex]

Compliant quadruped locomotion over rough terrain

Buchli, J., Kalakrishnan, M., Mistry, M., Pastor, P., Schaal, S.

In Intelligent Robots and Systems, 2009. IROS 2009. IEEE/RSJ International Conference on, pages: 814-820, 2009, clmc (inproceedings)

Abstract

Many critical elements for statically stable walking for legged robots have been known for a long time, including stability criteria based on support polygons, good foothold selection, recovery strategies to name a few. All these criteria have to be accounted for in the planning as well as the control phase. Most legged robots usually employ high gain position control, which means that it is crucially important that the planned reference trajectories are a good match for the actual terrain, and that tracking is accurate. Such an approach leads to conservative controllers, i.e. relatively low speed, ground speed matching, etc. Not surprisingly such controllers are not very robust - they are not suited for the real world use outside of the laboratory where the knowledge of the world is limited and error prone. Thus, to achieve robust robotic locomotion in the archetypical domain of legged systems, namely complex rough terrain, where the size of the obstacles are in the order of leg length, additional elements are required. A possible solution to improve the robustness of legged locomotion is to maximize the compliance of the controller. While compliance is trivially achieved by reduced feedback gains, for terrain requiring precise foot placement (e.g. climbing rocks, walking over pegs or cracks) compliance cannot be introduced at the cost of inferior tracking. Thus, model-based control and - in contrast to passive dynamic walkers - active balance control is required. To achieve these objectives, in this paper we add two crucial elements to legged locomotion, i.e., floating-base inverse dynamics control and predictive force control, and we show that these elements increase robustness in face of unknown and unanticipated perturbations (e.g. obstacles). Furthermore, we introduce a novel line-based COG trajectory planner, which yields a simpler algorithm than traditional polygon based methods and creates the appropriate input to our control system.We show results from bot- h simulation and real world of a robotic dog walking over non-perceived obstacles and rocky terrain. The results prove the effectivity of the inverse dynamics/force controller. The presented results show that we have all elements needed for robust all-terrain locomotion, which should also generalize to other legged systems, e.g., humanoid robots.

link (url) [BibTex]

am Buchli, J., Kalakrishnan, M., Mistry, M., Pastor, P., Schaal, S. Compliant quadruped locomotion over rough terrain In Intelligent Robots and Systems, 2009. IROS 2009. IEEE/RSJ International Conference on, pages: 814-820, 2009, clmc (inproceedings)

link (url) [BibTex]

A scaled bilateral control system for experimental one-dimensional teleoperated nanomanipulation

Onal, C. D., Sitti, M.

The International Journal of Robotics Research, 28(4):484-497, Sage Publications, 2009 (article)

[BibTex]

pi Onal, C. D., Sitti, M. A scaled bilateral control system for experimental one-dimensional teleoperated nanomanipulation The International Journal of Robotics Research, 28(4):484-497, Sage Publications, 2009 (article)

[BibTex]

A Swallowable Tethered Capsule Endoscope for Diagnosing Barrett’s Esophagus

Glass, P., Sitti, M., Pennathur, A., Appasamy, R.

Gastrointestinal Endoscopy, 69(5):AB106, Mosby, 2009 (article)

Project Page [BibTex]

pi Glass, P., Sitti, M., Pennathur, A., Appasamy, R. A Swallowable Tethered Capsule Endoscope for Diagnosing Barrett’s Esophagus Gastrointestinal Endoscopy, 69(5):AB106, Mosby, 2009 (article)

Project Page [BibTex]

A miniature ceiling walking robot with flat tacky elastomeric footpads

Unver, O., Sitti, M.

In Robotics and Automation, 2009. ICRA’09. IEEE International Conference on, pages: 2276-2281, 2009 (inproceedings)

[BibTex]

pi Unver, O., Sitti, M. A miniature ceiling walking robot with flat tacky elastomeric footpads In Robotics and Automation, 2009. ICRA’09. IEEE International Conference on, pages: 2276-2281, 2009 (inproceedings)

[BibTex]

Adhesion of biologically inspired polymer microfibers on soft surfaces

Cheung, E., Sitti, M.

Langmuir, 25(12):6613-6616, ACS Publications, 2009 (article)

[BibTex]

pi Cheung, E., Sitti, M. Adhesion of biologically inspired polymer microfibers on soft surfaces Langmuir, 25(12):6613-6616, ACS Publications, 2009 (article)

[BibTex]

Dangling chain elastomers as repeatable fibrillar adhesives

Sitti, M., Cusick, B., Aksak, B., Nese, A., Lee, H., Dong, H., Kowalewski, T., Matyjaszewski, K.

ACS applied materials \& interfaces, 1(10):2277-2287, American Chemical Society, 2009 (article)

[BibTex]

pi Sitti, M., Cusick, B., Aksak, B., Nese, A., Lee, H., Dong, H., Kowalewski, T., Matyjaszewski, K. Dangling chain elastomers as repeatable fibrillar adhesives ACS applied materials \& interfaces, 1(10):2277-2287, American Chemical Society, 2009 (article)

[BibTex]

Incorporating Muscle Activation-Contraction dynamics to an optimal control framework for finger movements

Theodorou, Evangelos A., Valero-Cuevas, Francisco J.

Abstracts of Neural Control of Movement Conference (NCM 2009), 2009, clmc (article)

Abstract

Recent experimental and theoretical work [1] investigated the neural control of contact transition between motion and force during tapping with the index finger as a nonlinear optimization problem. Such transitions from motion to well-directed contact force are a fundamental part of dexterous manipulation. There are 3 alternative hypotheses of how this transition could be accomplished by the nervous system as a function of changes in direction and magnitude of the torque vector controlling the finger. These hypotheses are 1) an initial change in direction with a subsequent change in magnitude of the torque vector; 2) an initial change in magnitude with a subsequent directional change of the torque vector; and 3) a simultaneous and proportionally equal change of both direction and magnitude of the torque vector. Experimental work in [2] shows that the nervous system selects the first strategy, and in [1] we suggest that this may in fact be the optimal strategy. In [4] the framework of Iterative Linear Quadratic Optimal Regulator (ILQR) was extended to incorporate motion and force control. However, our prior simulation work assumed direct and instantaneous control of joint torques, which ignores the known delays and filtering properties of skeletal muscle. In this study, we implement an ILQR controller for a more biologically plausible biomechanical model of the index finger than [4], and add activation-contraction dynamics to the system to simulate muscle function. The planar biomechanical model includes the kinematics of the 3 joints while the applied torques are driven by activation?contraction dynamics with biologically plausible time constants [3]. In agreement with our experimental work [2], the task is to, within 500 ms, move the finger from a given resting configuration to target configuration with a desired terminal velocity. ILQR does not only stabilize the finger dynamics according to the objective function, but it also generates smooth joint space trajectories with minimal tuning and without an a-priori initial control policy (which is difficult to find for highly dimensional biomechanical systems). Furthemore, the use of this optimal control framework and the addition of activation-contraction dynamics considers the full nonlinear dynamics of the index finger and produces a sequence of postures which are compatible with experimental motion data [2]. These simulations combined with prior experimental results suggest that optimal control is a strong candidate for the generation of finger movements prior to abrupt motion-to-force transitions. This work is funded in part by grants NIH R01 0505520 and NSF EFRI-0836042 to Dr. Francisco J. Valero- Cuevas 1 Venkadesan M, Valero-Cuevas FJ.  Effects of neuromuscular lags on controlling contact transitions.  Philosophical Transactions of the Royal Society A: 2008. 2 Venkadesan M, Valero-Cuevas FJ.  Neural Control of Motion-to-Force Transitions with the Fingertip.  J. Neurosci., Feb 2008; 28: 1366 - 1373; 3 Zajac. Muscle and tendon: properties, models, scaling, and application to biomechanics and motor control. Crit Rev Biomed Eng, 17 4. Weiwei Li., Francisco Valero Cuevas: ?Linear Quadratic Optimal Control of Contact Transition with Fingertip ? ACC 2009

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am Theodorou, Evangelos A., Valero-Cuevas, Francisco J. Incorporating Muscle Activation-Contraction dynamics to an optimal control framework for finger movements Abstracts of Neural Control of Movement Conference (NCM 2009), 2009, clmc (article)

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Inertial parameter estimation of floating-base humanoid systems using partial force sensing

Mistry, M., Schaal, S., Yamane, K.

In IEEE-RAS International Conference on Humanoid Robots (Humanoids 2009), Paris, Dec.7-10, 2009, clmc (inproceedings)

Abstract

Recently, several controllers have been proposed for humanoid robots which rely on full-body dynamic models. The estimation of inertial parameters from data is a critical component for obtaining accurate models for control. However, floating base systems, such as humanoid robots, incur added challenges to this task (e.g. contact forces must be measured, contact states can change, etc.) In this work, we outline a theoretical framework for whole body inertial parameter estimation, including the unactuated floating base. Using a least squares minimization approach, conducted within the nullspace of unmeasured degrees of freedom, we are able to use a partial force sensor set for full-body estimation, e.g. using only joint torque sensors, allowing for estimation when contact force measurement is unavailable or unreliable (e.g. due to slipping, rolling contacts, etc.). We also propose how to determine the theoretical minimum force sensor set for full body estimation, and discuss the practical limitations of doing so.

link (url) [BibTex]

am Mistry, M., Schaal, S., Yamane, K. Inertial parameter estimation of floating-base humanoid systems using partial force sensing In IEEE-RAS International Conference on Humanoid Robots (Humanoids 2009), Paris, Dec.7-10, 2009, clmc (inproceedings)

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On-line learning and modulation of periodic movements with nonlinear dynamical systems

Gams, A., Ijspeert, A., Schaal, S., Lenarčič, J.

Autonomous Robots, 27(1):3-23, 2009, clmc (article)

Abstract

link (url) [BibTex]

am Gams, A., Ijspeert, A., Schaal, S., Lenarčič, J. On-line learning and modulation of periodic movements with nonlinear dynamical systems Autonomous Robots, 27(1):3-23, 2009, clmc (article)

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Reversible dry micro-fibrillar adhesives with thermally controllable adhesion

Kim, S., Sitti, M., Xie, T., Xiao, X.

Soft Matter, 5(19):3689-3693, Royal Society of Chemistry, 2009 (article)

Project Page [BibTex]

pi Kim, S., Sitti, M., Xie, T., Xiao, X. Reversible dry micro-fibrillar adhesives with thermally controllable adhesion Soft Matter, 5(19):3689-3693, Royal Society of Chemistry, 2009 (article)

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Biologically Inspired Polymer Microfibrillar Arrays for Mask Sealing

Cheung, E., Aksak, B., Sitti, M.

CARNEGIE-MELLON UNIV PITTSBURGH PA, 2009 (techreport)

[BibTex]

pi Cheung, E., Aksak, B., Sitti, M. Biologically Inspired Polymer Microfibrillar Arrays for Mask Sealing CARNEGIE-MELLON UNIV PITTSBURGH PA, 2009 (techreport)

[BibTex]

Tankbot: A miniature, peeling based climber on rough and smooth surfaces

Unver, O., Sitti, M.

In Robotics and Automation, 2009. ICRA’09. IEEE International Conference on, pages: 2282-2287, 2009 (inproceedings)

[BibTex]

pi Unver, O., Sitti, M. Tankbot: A miniature, peeling based climber on rough and smooth surfaces In Robotics and Automation, 2009. ICRA’09. IEEE International Conference on, pages: 2282-2287, 2009 (inproceedings)

[BibTex]

Automated 2-D nanoparticle manipulation with an atomic force microscope

Onal, C. D., Ozcan, O., Sitti, M.

In Robotics and Automation, 2009. ICRA’09. IEEE International Conference on, pages: 1814-1819, 2009 (inproceedings)

[BibTex]

pi Onal, C. D., Ozcan, O., Sitti, M. Automated 2-D nanoparticle manipulation with an atomic force microscope In Robotics and Automation, 2009. ICRA’09. IEEE International Conference on, pages: 1814-1819, 2009 (inproceedings)

[BibTex]

Enhanced reversible adhesion of dopamine methacrylamide-coated elastomer microfibrillar structures under wet conditions

Glass, P., Chung, H., Washburn, N. R., Sitti, M.

Langmuir, 25(12):6607-6612, ACS Publications, 2009 (article)

Project Page [BibTex]

pi Glass, P., Chung, H., Washburn, N. R., Sitti, M. Enhanced reversible adhesion of dopamine methacrylamide-coated elastomer microfibrillar structures under wet conditions Langmuir, 25(12):6607-6612, ACS Publications, 2009 (article)

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Microparticle manipulation using multiple untethered magnetic micro-robots on an electrostatic surface

Floyd, S., Pawashe, C., Sitti, M.

In Intelligent Robots and Systems, 2009. IROS 2009. IEEE/RSJ International Conference on, pages: 528-533, 2009 (inproceedings)

[BibTex]

pi Floyd, S., Pawashe, C., Sitti, M. Microparticle manipulation using multiple untethered magnetic micro-robots on an electrostatic surface In Intelligent Robots and Systems, 2009. IROS 2009. IEEE/RSJ International Conference on, pages: 528-533, 2009 (inproceedings)

[BibTex]

2008

Learning to control in operational space

Peters, J., Schaal, S.

International Journal of Robotics Research, 27, pages: 197-212, 2008, clmc (article)

Abstract

One of the most general frameworks for phrasing control problems for complex, redundant robots is operational space control. However, while this framework is of essential importance for robotics and well-understood from an analytical point of view, it can be prohibitively hard to achieve accurate control in face of modeling errors, which are inevitable in com- plex robots, e.g., humanoid robots. In this paper, we suggest a learning approach for opertional space control as a direct inverse model learning problem. A ï¬rst important insight for this paper is that a physically cor- rect solution to the inverse problem with redundant degrees-of-freedom does exist when learning of the inverse map is performed in a suitable piecewise linear way. The second crucial component for our work is based on the insight that many operational space controllers can be understood in terms of a constrained optimal control problem. The cost function as- sociated with this optimal control problem allows us to formulate a learn- ing algorithm that automatically synthesizes a globally consistent desired resolution of redundancy while learning the operational space controller. From the machine learning point of view, this learning problem corre- sponds to a reinforcement learning problem that maximizes an immediate reward. We employ an expectation-maximization policy search algorithm in order to solve this problem. Evaluations on a three degrees of freedom robot arm are used to illustrate the suggested approach. The applica- tion to a physically realistic simulator of the anthropomorphic SARCOS Master arm demonstrates feasibility for complex high degree-of-freedom robots. We also show that the proposed method works in the setting of learning resolved motion rate control on real, physical Mitsubishi PA-10 medical robotics arm.

am ei

link (url) DOI [BibTex]

2008

am ei Peters, J., Schaal, S. Learning to control in operational space International Journal of Robotics Research, 27, pages: 197-212, 2008, clmc (article)

link (url) DOI [BibTex]