Publications

@article{9070191,
title = {MagnetoSuture: Tetherless Manipulation of Suture Needles},
author = {L O Mair and X Liu and B Dandamudi and K Jain and S Chowdhury and J Weed and Y Diaz-Mercado and I N Weinberg and A Krieger},
doi = {10.1109/TMRB.2020.2988462},
issn = {2576-3202},
year = {2020},
date = {2020-05-01},
journal = {IEEE Transactions on Medical Robotics and Bionics},
volume = {2},
number = {2},
pages = {206-215},
abstract = {This paper demonstrates the feasibility of ligation and tissue penetration for surgical suturing tasks using magnetically actuated suture needles. Manipulation of suture needles in minimally invasive surgery involves using articulated manual/robotic tools for needle steering and controlling needle-tissue or thread-tissue interactions. The large footprints of conventional articulated surgical tools significantly increase surgical invasiveness, potentially leading to longer recovery times, tissue damage, scarring, or associated infections. Aiming to address these issues, we investigate the feasibility of using magnetic fields to tetherlessly steer suture needles. The primary challenge of such a concept is to provide sufficient force for tissue penetration and ligation. In this work, we demonstrate proof-of-concept capabilities using the MagnetoSuture system, performing tissue penetration and ligation tasks using ex vivo tissues, customized NdFeB suture needles with attached threads, and remote-controlled magnetic fields. To evaluate the system performance, we conducted experiments demonstrating tetherless recreation of a purse string suture pattern, ligation of an excised segment of a rat intestine, and penetration of rat intestines.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{8732381,
title = {Sparsity Structure and Optimality of Multi-Robot Coverage Control},
author = {A Davydov and Y Diaz-Mercado},
doi = {10.1109/LCSYS.2019.2921513},
issn = {2475-1456},
year = {2020},
date = {2020-01-01},
journal = {IEEE Control Systems Letters},
volume = {4},
number = {1},
pages = {13-18},
abstract = {The structure of the Hessian matrix obtained from the locational cost used in coverage control is investigated to provide conditions on the optimality of coverage control solutions. It is shown that in arbitrary dimensions, the Hessian matrix is composed of the direct sum of three well-structured matrices: 1) a diagonal matrix; 2) a block-diagonal matrix; and 3) block-Laplacian matrix. This structure is exploited in the one-dimensional case, where an alternative proof of a sufficient condition for optimality is given. A relationship is shown between centroidal Voronoi tessellation (CVT) configurations and the sufficient condition for optimality via the spatial derivative of the density provided in the cost. A decomposition is used to provide insight into the terms which most affect optimality. Several classes of density functions are analyzed under the proposed condition. Experiments on a multi-robot team are shown to verify theoretical results.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{8391720,
title = {On Guaranteed Capture in Multi-Player Reach-Avoid Games via Coverage Control},
author = {P Rivera-Ortiz and Y Diaz-Mercado},
doi = {10.1109/LCSYS.2018.2849582},
issn = {2475-1456},
year = {2018},
date = {2018-10-01},
journal = {IEEE Control Systems Letters},
volume = {2},
number = {4},
pages = {767-772},
abstract = {The main objective of this letter is to provide a control solution for guaranteed capture in multi-player reach-avoid (RA) games in the presence of different vehicle kinematic constraints. To that end, this letter seeks to convert the RA problem from the traditional game theoretic framework to a coverage control problem, which makes it more suitable to find solutions in the multi-agent context. Within this framework, a distributed coverage control law is provided, as well as formal capture guarantees that are verified via simulation..},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{8255576,
title = {Coverage Control for Multirobot Teams With Heterogeneous Sensing Capabilities},
author = {M Santos and Y Diaz-Mercado and M Egerstedt},
doi = {10.1109/LRA.2018.2792698},
issn = {2377-3766},
year = {2018},
date = {2018-04-01},
journal = {IEEE Robotics and Automation Letters},
volume = {3},
number = {2},
pages = {919-925},
abstract = {This letter investigates how mobile agents with qualitatively different sensing capabilities should be organized in order to effectively cover an area. In particular, by encoding the different capabilities as different density functions in the locational cost, the result is a heterogeneous coverage control problem where the different density functions serve as a way of both abstracting and encapsulating different sensing capabilities. However, different density functions imply that mass is not conserved as the agents move and, as a result, the normal cancellations that occur across boundaries between regions of dominance in the homogeneous case no longer take place when computing the gradient of the locational cost. As a result, new terms are needed if the robots are to execute a descent flow in order to minimize the locational cost, and we show how these additional terms can be formulated as boundary-disagreement terms that are added to the standard Lloyd’s algorithm. The results are implemented on real robotic platforms for a number of different use cases.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{8022886,
title = {Multirobot Mixing via Braid Groups},
author = {Y Diaz-Mercado and M Egerstedt},
doi = {10.1109/TRO.2017.2737636},
issn = {1941-0468},
year = {2017},
date = {2017-12-01},
journal = {IEEE Transactions on Robotics},
volume = {33},
number = {6},
pages = {1375-1385},
abstract = {This paper presents a framework for multirobot motion planning that characterizes pairwise interactions between agents, e.g., crossing paths while en route to a destination. Mixing is identified as the number of pairwise crossings exhibited by the robot motion. Mixing patterns specified through elements of the braid group provide sufficient level of abstraction to describe interactions without concern for the geometry of the motion. Controllers are constructed explicitly reasoning about the spatial collocation of robots to execute mixing patterns, achieving rich motion in a shared space, e.g., to exchange inter-robot information. We do not focus on achieving a particular pattern, but rather on the problem of being able to execute a whole class of them (e.g., all patterns with at most $M$ pairwise interactions). The result is a hybrid system driven by symbolic inputs that are mapped onto paths, realizing desired mixing levels. Controllers derived from optimal control provide theoretical bounds on the achievable amount of mixing, satisfaction of spatio-temporal constraints, and collision-free trajectories. Designs are carried to implementation on real robot platforms.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{7050337,
title = {Multirobot Control Using Time-Varying Density Functions},
author = {S G Lee and Y Diaz-Mercado and M Egerstedt},
doi = {10.1109/TRO.2015.2397771},
issn = {1941-0468},
year = {2015},
date = {2015-04-01},
journal = {IEEE Transactions on Robotics},
volume = {31},
number = {2},
pages = {489-493},
abstract = {An approach is presented for influencing teams of robots by means of time-varying density functions, representing rough references for where the robots should be located. A continuous-time coverage algorithm is proposed and distributed approximations are given whereby the robots only need to access information from adjacent robots. Robotic experiments show that the proposed algorithms work in practice, as well as in theory.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}