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Ryu J.-C.,Northwestern University | Ruggiero F.,University of Naples Federico II | Lynch K.M.,Northwestern University | Lynch K.M.,Northwestern Institute on Complex Systems
Proceedings - IEEE International Conference on Robotics and Automation | Year: 2012

This paper presents stabilization control of a rolling manipulation system called the disk-on-disk. The system consists of two disks in which the upper disk (object) is free to roll on the lower disk (hand) under the influence of gravity. The goal is to stabilize the object at the unstable upright position directly above the hand. We use backstepping to derive a control law yielding global asymptotic stability. We present simulation as well as experimental results demonstrating the controller. © 2012 IEEE. Source


Lemey P.,Catholic University of Leuven | Rambaut A.,University of Edinburgh | Rambaut A.,U.S. National Institutes of Health | Bedford T.,University of Edinburgh | And 13 more authors.
PLoS Pathogens | Year: 2014

Information on global human movement patterns is central to spatial epidemiological models used to predict the behavior of influenza and other infectious diseases. Yet it remains difficult to test which modes of dispersal drive pathogen spread at various geographic scales using standard epidemiological data alone. Evolutionary analyses of pathogen genome sequences increasingly provide insights into the spatial dynamics of influenza viruses, but to date they have largely neglected the wealth of information on human mobility, mainly because no statistical framework exists within which viral gene sequences and empirical data on host movement can be combined. Here, we address this problem by applying a phylogeographic approach to elucidate the global spread of human influenza subtype H3N2 and assess its ability to predict the spatial spread of human influenza A viruses worldwide. Using a framework that estimates the migration history of human influenza while simultaneously testing and quantifying a range of potential predictive variables of spatial spread, we show that the global dynamics of influenza H3N2 are driven by air passenger flows, whereas at more local scales spread is also determined by processes that correlate with geographic distance. Our analyses further confirm a central role for mainland China and Southeast Asia in maintaining a source population for global influenza diversity. By comparing model output with the known pandemic expansion of H1N1 during 2009, we demonstrate that predictions of influenza spatial spread are most accurate when data on human mobility and viral evolution are integrated. In conclusion, the global dynamics of influenza viruses are best explained by combining human mobility data with the spatial information inherent in sampled viral genomes. The integrated approach introduced here offers great potential for epidemiological surveillance through phylogeographic reconstructions and for improving predictive models of disease control. © 2014 Lemey et al. Source


Vose T.H.,Northwestern University | Umbanhowar P.,Northwestern University | Lynch K.M.,Northwestern University | Lynch K.M.,Northwestern Institute on Complex Systems
IEEE International Conference on Automation Science and Engineering | Year: 2012

We examine the dynamics of point parts in frictional contact with a periodically vibrating, flat, rigid plate that is nominally tilted with respect to horizontal. If the friction law satisfies the maximum power inequality, then part dynamics on the tilted plate are equivalent to part dynamics on a horizontal plate with a different friction law that also satisfies the maximum power inequality. For small angles of tilt, this equivalence means that every periodic plate motion induces a position-dependent velocity field through which parts slide. Assuming Coulomb friction, some of the fields obtainable with a tilted plate are impossible to generate with a horizontal plate; other fields that require complicated motions on a horizontal plate can be generated with simpler motions on a tilted plate. © 2012 IEEE. Source


Vose T.H.,Northwestern University | Umbanhowar P.,Northwestern University | Lynch K.M.,Northwestern University | Lynch K.M.,Northwestern Institute on Complex Systems
Robotics: Science and Systems | Year: 2012

We model the full dynamics of a rigid part in three-point frictional sliding contact with a flat rigid 6-degree-offreedom plate. Given a periodic plate motion and the geometric, inertial, and frictional properties of the part, we define an asymptotic twist field mapping each part configuration to a unique part twist (linear and angular velocity). Asymptotic twist vectors in the field approximate the part's cycle-averaged twist at each configuration and are independent of time or the system's initial state. Simulations and experiments show that the trajectory of the part's configuration as it slides on the plate is well described by the field. With the ability to program arbitrary plate motions, part manipulation reduces to finding plate motions that generate asymptotic twist fields to accomplish desired tasks. Several simple fields useful for manipulation tasks (e.g., sensorless part alignment) are verified in simulation and experiment. For the special case of a rigid part with infinitesimal thickness, we show that the part's cycle-averaged twist for any configuration asymptotically converges to a unique asymptotic twist vector. Source


Vose T.H.,Apple Inc | Turpin M.H.,University of Pennsylvania | Dames P.M.,University of Pennsylvania | Umbanhowar P.,Apple Inc | And 2 more authors.
Mechanism and Machine Theory | Year: 2013

Small amplitude periodic motion of a 6-degree-of-freedom (DoF) rigid plate causes rigid parts on the surface to slide under the influence of friction as if immersed in a configuration-dependent velocity field. A plate whose motion is fully programmable is therefore a simple yet versatile manipulator. To develop such a manipulator, this paper addresses the design and control of a 6-DoF parallel mechanism intended for small-amplitude, high frequency vibration. We derive a linear model for the class of parallel mechanisms consisting of a rigid plate coupled to linear actuators through flexures. Using this model, we discuss manipulator design geared toward either universal parts feeding or single task automation. The design process is formulated as a constrained optimization over a design space that includes the geometry of the manipulator (actuator orientations and flexure attachment points) and the viscoelastic properties of the flexures. Finally, we present a frequency-based iterative learning controller for tracking periodic plate acceleration trajectories in R6 for all designs. Experimental data collected from our PPOD2 manipulator is used to validate the model and demonstrate the performance of the controller. © 2013 Elsevier Ltd. Source

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