Person: Werfel, Justin
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Werfel
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Justin
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Werfel, Justin
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Publication Fast, Accurate, Small-Scale 3D Scene Capture Using a Low-Cost Depth Sensor(IEEE, 2017-03) Carey, Nicole; Nagpal, Radhika; Werfel, JustinCommercially available depth sensing devices are primarily designed for domains that are either macroscopic, or static. We develop a solution for fast microscale 3D reconstruction, using off-the-shelf components. By the addition of lenses, precise calibration of camera internals and positioning, and development of bespoke software, we turn an infrared depth sensor designed for human-scale motion and object detection into a device with mm-level accuracy capable of recording at up to 30Hz.Publication TERMES: An Autonomous Robotic System for Three-Dimensional Collective Construction(MIT Press, 2011) Petersen, Kirstin Hagelskjaer; Nagpal, Radhika; Werfel, JustinCollective construction is the research area in which autonomous multi-robot systems build structures according to user specifications. Here we present a hardware system and high-level control scheme for autonomous construction of 3D structures under conditions of gravity. The hardware comprises a mobile robot and specialized passive blocks; the robot is able to manipulate blocks to build desired structures, and can maneuver on these structures as well as in unstructured environments. We describe and evaluate the robot's key capabilities of climbing, navigation, and manipulation, and demonstrate its ability to perform complex tasks that combine these capabilities by having it autonomously build a ten-block staircase taller than itself. In addition, we outline a simple decentralized control algorithm by which multiple simultaneously active robots could autonomously build user-specified structures, working from a high-level description as input.Publication Collective transport of complex objects by simple robots: Theory and experiments(2013) Rubenstein, Michael; Cabrera, Adrian; Werfel, Justin; Habibi, Golnaz; McLurkin, James; Nagpal, RadhikaAnts show an incredible ability to collectively transport complex irregular-shaped objects with seemingly simple coordination. Achieving similarly effective collective transport with robots has potential applications in many settings, from agriculture to construction to disaster relief. In this paper we investigate a simple decentralized strategy for collective transport in which each agent acts independently without explicit coordination. Using a physics-based model, we prove that this strategy is guaranteed to successfully transport a complex object to a target location, even though each agent only knows the target direction and does not know the object shape, weight, its own position, or the position and number of other agents. Using two robot hardware platforms, and a wide variety of complex objects, we validate the strategy through extensive experiments. Finally, we present a set of experiments to demonstrate the versatility of the simple strategy, including transport by 100 robots, transport of an actively moving object, adaptation to change in goal location, and dealing with partially observable goals.Publication Theory and associated phenomenology for intrinsic mortality arising from natural selection(Public Library of Science, 2017) Werfel, Justin; Ingber, Donald; Bar-Yam, YaneerStandard evolutionary theories of aging and mortality, implicitly based on assumptions of spatial averaging, hold that natural selection cannot favor shorter lifespan without direct compensating benefit to individual reproductive success. However, a number of empirical observations appear as exceptions to or are difficult to reconcile with this view, suggesting explicit lifespan control or programmed death mechanisms inconsistent with the classic understanding. Moreover, evolutionary models that take into account the spatial distributions of populations have been shown to exhibit a variety of self-limiting behaviors, maintained through environmental feedback. Here we extend recent work on spatial modeling of lifespan evolution, showing that both theory and phenomenology are consistent with programmed death. Spatial models show that self-limited lifespan robustly results in long-term benefit to a lineage; longer-lived variants may have a reproductive advantage for many generations, but shorter lifespan ultimately confers long-term reproductive advantage through environmental feedback acting on much longer time scales. Numerous model variations produce the same qualitative result, demonstrating insensitivity to detailed assumptions; the key conditions under which self-limited lifespan is favored are spatial extent and locally exhaustible resources. Factors including lower resource availability, higher consumption, and lower dispersal range are associated with evolution of shorter lifespan. A variety of empirical observations can parsimoniously be explained in terms of long-term selective advantage for intrinsic mortality. Classically anomalous empirical data on natural lifespans and intrinsic mortality, including observations of longer lifespan associated with increased predation, and evidence of programmed death in both unicellular and multicellular organisms, are consistent with specific model predictions. The generic nature of the spatial model conditions under which intrinsic mortality is favored suggests a firm theoretical basis for the idea that evolution can quite generally select for shorter lifespan directly.Publication Collective Decision-Making in Multi-Agent Systems by Implicit Leadership(Association for Computing Machinery Press, 2010) Yu, Chih-Han; Werfel, Justin; Nagpal, RadhikaCoordination within decentralized agent groups frequently requires reaching global consensus, but typical hierarchical approaches to reaching such decisions can be complex, slow, and not fault-tolerant. By contrast, recent studies have shown that in decentralized animal groups, a few individuals without privileged roles can guide the entire group to collective consensus on matters like travel direction. Inspired by these findings, we propose an implicit leadership algorithm for distributed multi-agent systems, which we prove reliably allows all agents to agree on a decision that can be determined by one or a few better-informed agents, through purely local sensing and interaction. The approach generalizes work on distributed consensus to cases where agents have different confidence levels in their preferred states. We present cases where informed agents share a common goal or have conflicting goals, and show how the number of informed agents and their confidence levels affects the consensus process. We further present an extension that allows for fast decision-making in a rapidly changing environment. Finally, we show how the framework can be applied to a diverse variety of applications, including mobile robot exploration, sensor network clock synchronization, and shape formation in modular robots.Publication Distributed Multi-Robot Algorithms for the TERMES 3D Collective Construction System(Institute of Electrical and Electronics Engineers, 2011) Werfel, Justin; Petersen, Kirsten; Nagpal, RadhikaThe research goal of collective construction is to develop systems in which large numbers of autonomous robots build large-scale structures according to desired specifications. We present algorithms for TERMES, a multi-robot construction system inspired by the building activities of termites. The system takes as input a high-level representation of a desired structure, and provides rules for an arbitrary number of simple climbing robots to build that structure, using passive solid building blocks under conditions of gravity. These rules are decentralized, rely on local information and implicit coordination, and provably guarantee correct completion of the target structure. Robots build staircases of blocks (potentially removable as temporary scaffolds) that they can climb to build structures much larger than themselves.Publication Coordinating Collective Locomotion in an Amorphous Modular Robot(Institute of Electrical and Electronics Engineers (IEEE), 2010) Yu, Chih-Han; Werfel, Justin; Nagpal, RadhikaModular robots can potentially assemble into a wide range of configurations to locomote in different environments. However, designing locomotion strategies for each configuration is often tedious and has generally relied on a priori known connection geometry. Here we present a framework for 2D modular robots made of square modules assembled with arbitrary geometry, which achieve collective and directed locomotion with no centralized controller. Individual modules communicate locally and provably achieve consensus in coordinating movement in a common travel direction. In experiments with simulations and hardware prototypes, we show that robots achieve effective locomotion, irrespective of the number of modules and their connectivity which can be highly asymmetricPublication Positional Communication and Private Information in Honeybee Foraging Models(Springer, 2010) Bailis, Peter David; Nagpal, Radhika; Werfel, JustinHoneybees coordinate foraging efforts across vast areas through a complex system of advertising and recruitment. One mechanism for coordination is the waggle dance, a movement pattern which carries positional information about food sources. However, recent evidence suggests that recruited foragers may not use the dance’s positional information to the degree that has traditionally been believed. We model bee colony foraging to investigate the value of sharing food source position information in different environments. We find that in several environments, relying solely on private information about previously encountered food sources is more efficient than sharing information. Relying on private information leads to a greater diversity of forage sites and can decrease over-harvesting of sources. This is beneficial in environments with small quantities of nectar per flower, but may be detrimental in nectar-rich environments. Efficiency depends on both the environment and a balance between exploiting high-quality food sources and oversubscribing them.Publication Autonomous Sheet Pile Driving Robots for Soil Stabilization(IEEE, 2019) Melenbrink, Nathan; Werfel, JustinAbstract— Soil stabilization is a fundamental component of nearly all construction projects, ranging from commercial construction to environmental restoration projects. Previous work in autonomous construction has generally not considered these essential stabilization and anchoring tasks. In this work we present Romu, an autonomous robot capable of building continuous linear structures by using a vibratory hammer to drive interlocking sheet piles into soil. We report on hardware parameters and their effects on pile driving performance, and demonstrate autonomous operation in both controlled and natural environments. Finally, we present simulations in which a small swarm of robots build with sheet piles in example terrains, or apply an alternate spray-based stabilizing agent, and quantify the ability of each intervention to mitigate hydraulic erosion.