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We present a novel analysis technique to understand the dynamics of a recently described locomotion mode called legless locomotion. Legless locomotion is a locomotion mode available to a legged robot when it becomes high-centered, that is, when its legs do not touch the ground. Under these conditions, the robot may still locomote in the plane by swinging its legs in the air, rocking on its body, and taking advantage of the nonholonomic contact constraints. Legless locomotion is unique from all previously studied locomotion modes, since it combines the effect of oscillations due to controls and gravity, nonholonomic contact constraints, and a configuration-dependent inertia. This complex interaction of phenomena makes dynamics analysis and motion planning difficult, and our proposed analysis technique simplifies the problem by decoupling the robot's oscillatory rotational dynamics from its contact kinematics and also decoupling the dynamics along each axis. We show that the decoupled dynamics models are significantly simpler, provide a good approximation of the motion, and offer insight into the robot's dynamics. Finally, we show how the decoupled models help in motion planning for legless locomotion. [ABSTRACT FROM AUTHOR]

This paper presents an approach to couple path planning and control for mobile robot navigation in a hybrid control framework. We build upon an existing hybrid control approach called sequential composition, in which a set of feedback control policies are prescribed on well-defined domains contained in the robot's free space. Each control policy drives the robot to a goal set, which lies in the domain of a subsequent policy. Control policies are deployed into the free state space so that when composed among one another, the overall action of the set of control policies drives the robot to perform a task, such as moving from a start to a goal location or patrolling a perimeter. A planner determines the sequence of control policies to be invoked. When control policies defined in this framework respect the low-level dynamics and kinematics of the system, this formal approach guarantees that high-level tasks are either accomplished by a given set of policies, or verifies that the tasks are not achievable with the given policies. Specifically, this paper makes three key contributions to the technique of sequential composition. First, we allow for a larger variety of transitions among the control policies, which results in a richer set of generated behaviors. In particular, we are able to design policies that respect multiple interacting constraints including obstacles, nonholonomic constraints, and input bounds. This is achieved by utilizing flow-through control policies, which allow the robot to exit the policy domain through a subset of the domain boundary. Second, our hybrid control approach lifts the planning problem from working in trajectory space to control policy space, allowing for both more efficient and meaningful symbolic planners to be employed for systems with nonholonomic constraints. Finally, we address the issue of deploying control policies in configuration spaces whose obstacles have curvature (i.e., are not polytopes in configuration space); ultimately, such an approach results in the collection of policy domains only approximating the free space. We believe this trade-off is necessary, and provide a technique to measure the relative completeness of the approximation. The paper concludes with an experimental validation of our approach on a mobile robot. [ABSTRACT FROM AUTHOR]

LittleDog is a small four-legged robot designed for research on legged locomotion. The LittleDog platform was designed by Boston Dynamics with funding from DARPA to enable rapid advances in the state of the art of rough-terrain locomotion algorithms. In addition to providing a fleet of 12 robots with baseline software and development tools, LittleDog served as a cross-team common platform that allowed direct comparison of results across multiple research teams. Here we report the details of this robotic system. [ABSTRACT FROM AUTHOR]

This paper presents an approach to accurate and scalable multiple-model (MM) state estimation for hybrid systems with intermittent, cyclical, multimodal dynamics. The approach consists of using discrete-state estimation to identify a system’s dynamical and behavioral contexts and determine which motion models appropriately represent current dynamics and which individual and MM filters are appropriate for state estimation. Furthermore, the heirarchical structure of the dynamics is explicitly encoded, which enables detection not only of rapid transitions between motion models but of higher level behavioral transitions as well. This improves the accuracy and scalability of conventional MM state estimation, which is demonstrated experimentally on a mobile robot that exhibits fast-switching, multimodal dynamics. [ABSTRACT FROM AUTHOR]

This paper addresses the coupled navigation and control problem for fully actuated dynamical systems operating in cluttered environments. The proposed method composes local feedback control policies to address the global problem in a formally correct manner. Our contribution extends the method of sequential composition to a new class of flow-through policies, which are defined for an idealized point robot that is subject to bounds on velocity and acceleration. These policies, which are defined over convex polytopes, express natural behaviors and guarantee safe trajectories while respecting system constraints. This paper presents a constructive technique for building hybrid control systems with guaranteed transitions and stability properties. Simulation results demonstrate policy-based decision making for various initial conditions. [ABSTRACT FROM AUTHOR]

Complete automation of trajectory planning tools for material deposition/removal applications has become increasingly necessary to reduce the "concept-to-consumer" timeline for rapid product introduction in industries such as the automotive industry. The work in this paper is specifically motivated by automotive spray painting. Prior developments in automated trajectory planning tools promise to reduce the time required to program the robots; however, these approaches are limited to surfaces that are either approximately planar or topologically simple (i.e., with no holes). To extend the applicability of these planning tools to nonplanar and topologically complex surfaces, currently the user has to manually segment a complex surface into simpler subsets, i.e., subsets that are approximately extruded surfaces and contain no holes. However, the complex nature of the relationships between surface segmentation and resulting output characteristics such as material deposition uniformity, process cycle time, and material waste makes the task of manually segmenting the surface difficult. In this paper, we develop a hierarchical procedure that automatically segments a surface based on surface geometry, surface topology, and path geometry to obtain topologically simple subsets that are approximately extruded surfaces. Finally, we compare the effectiveness of our segmentation with the state of the art on a few automotive surfaces in simulation. Note to Practitioners--The surface segmentation strategies described in this work can be applied to surfaces that are composed of approximately extruded surface patches joined together by regions of high curvature; such surfaces include typical automotive surfaces. The segmentation procedure allows the user to automatically generate a collection of preliminary coverage trajectories. With careful selection and minor clean up, these trajectories can improve the coverage uniformity for a given surface. The procedure operates on a surface CAD model, preferably in the triangulated manifold format and requires information about the material distribution (or removal) pattern produced from the atomizer (or machining) tool. With an understanding of the relative costs associated with different output characteristics such as uniformity of deposition, cycle time, and material waste, the procedures can be incorporated in existing industrial planning and simulation toots (with appropriate support from the software vendor) for applications such as robotic spray painting and CNC machining. [ABSTRACT FROM AUTHOR]

The article discusses the development of the mechanical system of the actuator with mechanically adjustable series compliance (AMASC), a prototype leg for a running robot. It is said to be important to begin a robot design with a specification for the dynamic behavior of the machine, since the mechanical system cannot be changed easily once it is built. In this case, the actuator was designed to be equipped with mechanical springs, which will store and release kinetic energy as it follows a center-of-mass motion during a running gait. Based on the design of the AMASC, a single prototype leg of the BiMASC was designed and developed, which was eventually revised into the ECD leg.

We present a novel locomotion strategy called legless locomotion that allows a round-bodied legged robot to locomote approximately when it is high-centered. Typically, a high-centered robot is stuck since the robot's legs do not touch the ground. Legless locomotion uses the legs as a reaction mass to set up oscillatory body rotations which when coupled with ground contact gradually translate the robot. Legless locomotion `s continuous dynamics differs from previously studied locomotion methods because of the simultaneous interaction of gravity-induced oscillations, a configuration-dependent system inertia, and non-holonomic contact constraints. This paper employs simple models to capture the complex dynamics and uses the intuition developed from the models to develop gaits that provide planar accessibility. We also present a quantification of legless locomotion's properties using simulations and motion-capture experiments. [ABSTRACT FROM AUTHOR]

The article reports on the decentralized multiagent traffic coordination approach in multirobotics system using a conventional Ackermann-steered vehicles. The approach uses low-level continuous feedback control policies that are combined with a correct distinct automation, which satisfies specified high-level behavior for any initial stage in the domain of low-level policies. It combines the strengths of control theoretic and computer science approaches, which offers guarantees that can be proven over local domains. The approach creates a hybrid-feedback-control policy that fulfills a given high-level specification without planning a specific configuration path by using a collection of local feedback control polices that provides continuous guarantees.

In this paper, we generalize our prior results in motion analysis to design gaits for a more general family of underactuated mechanical systems. In particular we analyze and generate gaits for mixed mechanical systems which are systems whose motion is simultaneously governed by both a set of non-holonomic velocity constraints and a notion of a generalized momentum being instantaneously conserved along allowable directions of motion. Through proper recourse to geometric mechanics, we are able to show that the resulting motion from a gait has two portions: a geometric and a dynamic contribution. The main challenge in motion planning for a mixed system is understanding how to separate the geometric and dynamic contributions of motion due to a general gait, thus simplifying gait analysis. In this paper we take the first step towards addressing this challenge in a generalized framework. Finally, we verify the generality of our approach by applying our techniques to novel mechanical systems which we introduce in this paper as well as by verifying that seemingly different prior motion planning results could actually be explained using the gait analysis presented in this paper [ABSTRACT FROM AUTHOR]

In this paper we generate gaits for two types of underactuated mechanical systems: principally kinematic and purely mechanical systems. Our goal is to specify inputs in the form of gaits, that is, a sequence of controlled shape changes of a multi-bodied mechanical system that when executed would produce a desired change in the unactuated position or orientation variables of the entire mechanical system. In other words, we want to indirectly control the unactuated degrees of freedom of the mechanical system utilizing a controlled ‘internal’ shape change. More precisely, in this paper we develop a gait evaluation tool which easily measures the change of position, computed in a body-attached coordinate frame, due to any closed curve in the shape space. This evaluation tool is simple enough that we can use it to generate gaits or to design curves that move the mechanical system along a desired direction. Finally, we verify that this gait analysis technique applies to two seemingly different classes of mechanical systems, purely mechanical and principally kinematic systems, and unify the gait generation problem for both classes. [ABSTRACT FROM AUTHOR]

Effective modeling and control of multibody systems interacting with their environment through frictional contact remains a challenging problem. In this paper we address the planar version of this problem by developing a general method to compute the instantaneous dynamic solution for planar rigid bodies interacting with their environment through Coulomb frictional contacts. The resulting analytical forward solution is represented in piecewise linear form, which admits tractable inversion for implementing behavioral control. We address the inherent problem of ambiguity in the resulting model (both between and within a particular linear model) by resorting to enumeration techniques and solve for the complete collection of possible model solutions in the presence of both contact constraints and additional task-specific linear constraints. We illustrate the application of these techniques by developing a controller to reliably achieve the dynamic self-righting of a hexapod robot. [ABSTRACT FROM AUTHOR]

In spray painting applications, it is essential to generate a spray gun trajectory such that the entire surface is completely covered and receives an acceptably uniform layer of paint deposition; we call this the "uniform coverage" problem. The uniform coverage problem is challenging because the atomizer emits a non-trivial paint distribution, thus making the relationships between the spray gun trajectory and the deposition uniformity complex. To understand the key issues involved in uniform coverage, we consider surface patches that are geodesically convex and topologically simple as representative of subsets of realistic automotive surfaces. In addition to ensuring uniform paint deposition on the surface, our goal is to also minimize the associated process cycle time and paint waste. Based on the relationships between the spray gun trajectory and the output characteristics (i.e., uniformity, cycle time and paint waste), our approach decomposes the coverage trajectory generation problem into three subproblems: (1) selecting a seed curve, (2) determining a speed profile along each pass, and (3) selecting the spacing between successive passes. Using concepts such as area magnification and the Gauss-Bonnet theorem from differential geometry, as well as standard optimization procedures, we present procedures to solve each subproblem independently from the others. We demonstrate our trajectory planning procedures by approximating real automotive surfaces by simple surfaces in simulation, and finally evaluate the effectiveness of our algorithms experimentally on real automotive surfaces. [ABSTRACT FROM AUTHOR]

This research is focused on developing trajectory planning tools for the automotive painting industry. The geometric complexity of automotive surfaces and the complexity of the spray patterns produced by modern paint atomizers combine to make this a challenging and interesting problem. This paper documents our efforts to develop computationally tractable analytic deposition models for electrostatic rotating bell (ESRB) atomizers, which have recently become widely used in the automotive painting industry. The models presented in this paper account for both the effects of surface curvature as well as the deposition pattern of ESRB atomizers in a computationally tractable form, enabling the development of automated trajectory generation tools. We present experimental results used to develop and validate the models, and verify the interaction between the deposition pattern, the atomizer trajectory, and the surface curvature. Limitations of the deposition model with respect to predictions of paint deposition on highly curved surfaces are discussed. Note to Practitioners-The empirical paint deposition models developed herein, which are fit to experimental data, offer a significant improvement over models that are typically used in industrial robot simulations. The improved simulation results come without the computational cost and complexity of finite element methods. The models could be incorporated, as is, into existing industrial simulation tools, provided the users are cognizant of the model limitations with respect to highly curved surfaces. Although the models are based on readily available information, incorporating the models into existing robot simulation software would likely require support from the software vendor. [ABSTRACT FROM AUTHOR]

We report on the design and analysis of a controller that can achieve dynamical self-righting of our hexapedal robot, RHex. Motivated by the initial success of an empirically tuned controller we present a feedback controller based on a saggital plane model of the robot We also extend this controller to develop a hybrid pumping strategy that overcomes actuator torque limitations, resulting in robust flipping behavior over a wide range of surfaces. We present simulations and experiments to validate the model and characterize the performance of the new controller. [ABSTRACT FROM AUTHOR]

Exact cellular decompositions represent a robot's free space by dividing it into regions with simple structure such that the sum of the regions fills the free space. These decompositions have been widely used for path planning between two points, but can be used for mapping and coverage of free spaces. In this paper, we define exact cellular decompositions where critical points of Morse functions indicate the location of cell boundaries. Morse functions are those whose critical points are non-degenerate. Between critical points, the structure of a space is effectively the same, so simple control strategies to achieve tasks, such as coverage, are feasible within each cell. This allows us to introduce a general framework for coverage tasks because varying the Morse function has the effect of changing the pattern by which a robot covers its free space. In this paper, we give examples of different Morse functions and comment on their corresponding tasks. In a companion paper, we describe the sensor-based algorithm that constructs the decomposition. [ABSTRACT FROM AUTHOR]

A promising approach to enabling the rapid deployment and reconfiguration of automated assembly systems is to make use of cooperating, modular, robust robotic agents. Over the past 5 years, the authors have been constructing just such a system suitable for assembly of high-precision, high-value products. Within this environment, each robotic agent executes its own program, coordinating its activity with that of its peers to produce globally cooperative precision behavior. To simplify the problems associated with deploying such systems, each agent adheres to a strict notion of modularity, both physically and computationally. The intent is to provide an architecture within which it is straightforward to specify strategies for the robust execution of potentially complex and fragile cooperative behaviors. The underlying behaviors use a runtime environment that includes tools to automatically sequence the activities of an agent. Taken together, these abstractions enable a designer to rapidly and effectively describe the high-level behavior of a collection of agents while relying on a set of formally correct control strategies to properly execute and sequence the necessary continuous behaviors. [ABSTRACT FROM AUTHOR]

Presents a working implementation of a dynamics based architecture for visual sensing. Field rate estimates provided by the architecture; How the interconnection of two nonlinear dynamical systems affected the system's success.