TechTalks from event: Technical session talks from ICRA 2012

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Grasping: Modeling, Analysis and Planning

  • On the Caging Region of a Third Finger with Object Boundary Clouds and Two Given Contact Positions Authors: Wan, Weiwei; Fukui, Rui; Shimosaka, Masamichi; Sato, Tomomasa
    This paper presents a caging approach which deals with planar boundary clouds collected from a laser scanner. Given the boundary clouds of a target object and two fixed finger positions, our aim is to find potential third finger positions that can prevent target from escaping into infinity. The major challenge in working with boundary clouds lies in their uncertainty in geometric model fitting and the failure of critical orientations. In this paper, we track canonical motions according to the rotational intersection of Configuration space fingers and rasterize Work space with grids to compute the third caging positions. Our approach can generate the capture region with max(O(np),O(h^2))<=O(n^2) cost where n denotes the resolution of grid rasterization, p denotes the resolution of canonical rasterization and h denotes the resolution of boundary rasterization or the number of boundary cloud points. Moreover, we propose a rough approximation which measures a subset of the possible positions by contracting rotations, indicating computational complexity of max(O(n),O(h^2)). In the experimental part, our proposal is compared with state-of-the-art works and applied to many other objects. The approach makes caging fast and effective.
  • Independent Contact Regions Based on a Patch Contact Model Authors: Charusta, Krzysztof Andrzej; Krug, Robert; Dimitrov, Dimitar Nikolaev; Iliev, Boyko
    The synthesis of multi-fingered grasps on non-trivial objects requires a realistic representation of the contact between the fingers of a robotic hand and an object. In this work, we use a patch contact model to approximate the contact between a rigid object and a deformable anthropomorphic finger. This contact model is utilized in the computation of Independent Contact Regions (ICRs) that have been proposed as a way to compensate for shortcomings in the finger positioning accuracy of robotic grasping devices. We extend the ICR algorithm to account for the patch contact model and show the benefits of this solution.
  • A Grasping Force Optimization Algorithm for Dexterous Robotic Hands Authors: Lippiello, Vincenzo; Siciliano, Bruno; Villani, Luigi
    The problem of grasping force optimization for a robotic system equipped with multi-fingered hands is considered in this paper. This problem is cast in a convex optimization problem, considering also joint torque constraints. A solution suitable for an online implementation, which allows a substantial reduction of the computational load by dynamically decreasing the number of active torque constraints is proposed. Moreover, for the case of a bimanual manipulation system, a sub-optimal single-hand optimization algorithm is presented and compared with the optimal one. The effectiveness of the described methods has been tested in a simulation case study.
  • Local Force Closure Authors: Kruger, Heinrich; Rimon, Elon; van der Stappen, Frank
    We introduce the concept of Local Force Closure. We define a local force closure grasp as a grasp which is capable of resisting some given external wrench as well as (through local variation in contact wrenches) any wrench in some neighborhood of the given wrench, with grasp quality exceeding some given threshold. Local force closure is useful in applications where a grasp only needs to resist some given external wrench, rather than fully constraining object, but where there is some uncertainty regarding the exact external wrench that needs to be resisted, or where there is a possibility of having to cope with some (relatively small) unknown disturbance forces. We show that by allowing disc-shaped fingers in contact with convex vertices of a polygonal object, any given wrench can be resisted by just two frictionless fingers. For a given polygonal object with <i>n</i> vertices and an external wrench <i>w</i><sub>ext</sub>, we show how to find all pairs of features of <i>P</i>, that admit grasps capable of resisting <i>w</i><sub>ext</sub> with grasp quality greater or equal to some threshold <i>Q</i>, in <i>O(n<sup>3/2+&#949;</sup>+K)</i> time, where <i>K</i> is the number of pairs in the output and <i>&#949;</i> is some arbitrarily small, positive constant. We then show how to adapt our algorithm to guarantee that the features reported, admit local force closure grasps.
  • Two-Fingered Caging of Polygons Via Contact-Space Graph Search Authors: Allen, Thomas F; Rimon, Elon; Burdick, Joel
    Based on a novel contact-space formulation, this paper presents a new algorithm to find two-fingered caging grasps of planar polygonal objects. We show that the caging problem has several useful properties in contact space. First, the critical points of the cage representation in the hand’s configuration space appear as critical points of an inter-finger distance function in contact space. Second, the critical points of this distance function can be simply characterized. Third, the contact space admits a rectangular decomposition where the distance function is convex in each rectangle, and all critical points lie on the rectangle boundaries. This property leads to a natural “caging graph,” which can be readily searched to construct the caging sets. An example, constructed from real-world data illustrates and validates the method.
  • Object Categorization and Grasping by Parts from Range Scan Data Authors: Aleotti, Jacopo; Lodi Rizzini, Dario; Caselli, Stefano
    Object category recognition and localization in 3D range data is of great importance in robot manipulation. In this work we propose a novel approach for object categorization and grasping that is focused on topological shape segmentation. The method allows generation of watertight triangulated models of the objects and their shape segmentation into parts. This segmentation provides meaningful information about grasp affordances. An efficient technique for encoding proximity data from range scans is also presented as well as an advanced strategy for manipulation of object sub-parts. Experiments are reported in a real environment using a robot arm equipped with eye-in-hand laser scanner and a parallel gripper.

Learning and Adaptive Control of Robotic Systems I

  • RTMBA: A Real-Time Model-Based Reinforcement Learning Architecture for Robot Control Authors: Hester, Todd; Quinlan, Michael; Stone, Peter
    Reinforcement Learning (RL) is a paradigm for learning decision-making tasks that could enable robots to learn and adapt to their situation on-line. For an RL algorithm to be practical for robotic control tasks, it must learn in very few samples, while continually taking actions in real-time. Existing model-based RL methods learn in relatively few samples, but typically take too much time between each action for practical on-line learning. In this paper, we present a novel parallel architecture for model-based RL that runs in real-time by 1) taking advantage of sample-based approximate planning methods and 2) parallelizing the acting, model learning, and planning processes in a novel way such that the acting process is sufficiently fast for typical robot control cycles. We demonstrate that algorithms using this architecture perform nearly as well as methods using the typical sequential architecture when both are given unlimited time, and greatly out-perform these methods on tasks that require real-time actions such as controlling an autonomous vehicle.
  • Sensorimotor Learning of Sound Localization from an Auditory Evoked Behavior Authors: Bernard, Mathieu; PIRIM, Patrick; de Cheveigné, Alain; Gas, Bruno
    A new method for self-supervised sensorimotor learning of sound source localization is presented, that allows a simulated listener to learn online an auditorimotor map from the sensorimotor experience provided by an auditory evoked behavior. The map represents the auditory space and is used to estimate the azimuthal direction of sound sources. The learning mainly consists in non-linear dimensionality reduction of sensorimotor data. Our results show that an auditorimotor map can be learned, both from real and simulated data, and that the online learning leads to accurate estimations of azimuthal sources direction.
  • Path-following Control of a Velocity Constrained Tracked Vehicle Incorporating Adaptive Slip Estimation Authors: Burke, Michael
    This work presents a model predictive path-following controller, which incorporates adaptive slip estimation for a tracked vehicle. Tracked vehicles are capable of manoeuvring in highly variable and uneven terrain, but difficulties in their control have traditionally limited their use as autonomous platforms. Attempts to compensate for slip in environments typically require that both the forward and rotational velocities of a platform be determined, but this can be challenging. This paper shows that it is possible to estimate vehicle traction using only a rate gyroscope, by providing a suitable adaptive least squares estimator to do so. An approach to generating slip compensating controls when platform velocity constraints are applied is also presented. The approach is controller independent, but we make use of a model predictive controller, vulnerable to the effects of model-plant mismatch, to highlight the efficacy of the proposed estimation and compensation. Path following results using a mixture model to generate feasible slip values are presented, and show a significant increase in controller performance.
  • Direct Yaw Moment Control for Four Wheel Independent Steering and Drive Vehicles Based on Centripetal Force Detection Authors: Lam, Tin Lun; Xu, Yangsheng
    In this paper, a deterministic yaw moment controller for four wheel independent steering and drive vehicles is proposed to enhance driving stability and controllability. Different to conventional methods that track a desired yaw rate, the proposed controller stabilizes a vehicle by additionally tracking the heading angle of a vehicle which is more efficient and robust. The heading angle of a vehicle is obtained by a novel method which is based on centripetal force detection. It eliminates the prerequisite knowledge of the characteristics between wheels and road surface which are time varying and difficult to be measured in real time. The proposed system only requires low cost sensing equipment such as wheel speed sensor and accelerometer that makes the system practical to be utilized. The proposed heading angle detection method can be generally applied to any kind of vehicle. The deterministic yaw moment controller is also applicable to any type of four wheel independent drive vehicles.
  • Predictive Control of Chained Systems: A Necessary Condition on the Control Horizon Authors: Courtial, Estelle; Fruchard, Matthieu; Allibert, Guillaume
    This paper deals with state feedback control of chained systems based on a Nonlinear Model Predictive Control (NMPC) strategy. Chained systems can model many common nonholonomic vehicles. We establish a relation between the degree of nonholonomy and the minimum length of the control horizon so as to make the NMPC feasible. A necessary condition on the control horizon of NMPC is given and theoretically proved whatever the dimension of the chained system consid- ered. This relation is used to design a NMPC-based control strategy for chained systems. One of the advantages of NMPC is the capability of taking into account the constraints on state and on control variables. The theoretical results are illustrated through simulations on a (2,5) chained system, describing a car-like vehicle with one trailer. Difficult motion objectives that require a lateral displacement are considered.
  • Xbots: An Approach to Generating and Executing Optimal Multi-Robot Plans with Cross-Schedule Dependencies Authors: Korsah, G. Ayorkor; Kannan, Balajee; Browning, Brett; Stentz, Anthony; Dias, M. Bernardine
    In this paper, we present an approach to bounded optimal planning and flexible execution for a robot team performing a set of spatially distributed tasks related by temporal ordering constraints such as precedence or synchronization. Furthermore, the manner in which the temporal constraints are satisfied impacts the overall utility of the team, due to the existence of both routing and delay costs. We present a bounded optimal offline planner for task allocation and scheduling in the presence of such cross-schedule dependencies, and a flexible, distributed online plan execution strategy. The integrated system performs task allocation and scheduling, executes the plans smoothly in the face of real-world variations in operation speed and task execution time, and ensures graceful degradation in the event of task failure. We demonstrate the capabilities of our approach on a team of three pioneer robots operating in an indoor environment. Experimental results demonstrate that approach is effective for constrained planning and execution in the face of real-world variations.

Animation & Simulation

  • Conditions for Uniqueness in Simultaneous Impact with Application to Mechanical Design Authors: Seghete, Vlad; Murphey, Todd
    We present a collision resolution method based on momentum maps and show how it extends to handling multiple simultaneous collisions. Simultaneous collisions, which are common in robots that walk or climb, do not necessarily have unique outcomes, but we show that for special configurations—--e.g. when the surfaces of contact are orthogonal in the appropriate sense—--simultaneous impacts have unique outcomes, making them considerably easier to understand and simulate. This uniqueness helps us develop a measure of the unpredictability of the impact outcome based on the state at impact and is used for gait and mechanism design, such that a mechanism’s actions are more predictable and hence controllable. As a preliminary example, we explore the configuration space at impact for a model of the RHex running robot and find optimal configurations at which the unpredictability of the impact outcome is minimized.
  • Dynamics Simulation for the Training of Teleoperated Retrieval of Spent Nuclear Fuel Authors: Cornella, Jordi; Zerbato, Davide; Giona, Luca; Fiorini, Paolo; Sequeira, Vitor
    This paper addresses the problem of training of operators for telemanipulation tasks. In particular it describes the development of a physics based virtual environment that allows a user to train in the control of an innovative robotic tools designed for the retrieval of spent nuclear fuels. The robotic device is designed to adapt to very different environments, at the cost of an increased complexity in its control. The virtual environment provides realistic simulation of robot dynamics. The two most challenging tasks related to robot control have been identified and implemented in the simulation, leading to an effective tool for the training. The developed application is described in details and the outcome of one simulated intervention is proposed and analyzed in terms of user interaction and realism.
  • Putting the Fish in the Fish Tank: Immersive VR for Animal Behavior Experiments Authors: Butail, Sachit; Paley, Derek; Chicoli, Amanda
    We describe a virtual-reality framework for investigating startle-response behavior in fish. Using real-time three-dimensional tracking, we generate looming stimuli at a specific location on a computer screen, such that the shape and size of the looming stimuli change according to the fish's perspective and location in the tank. We demonstrate the effectiveness of the setup through experiments on Giant danio and compute the success rate in eliciting a response. We also estimate visual startle sensitivity by presenting the stimulus from different directions around the fish head. The aim of this work is to provide the basis for quantifying escape behavior in fish schools.
  • Design and Implementation of Dynamic Simulators for the Testing of Inertial Sensors Authors: allotta, benedetto; Becciolini, Lorenzo; Costanzi, Riccardo; Giardi, Francesca; Ridolfi, Alessandro; Vettori, Gregorio
    Many dynamic simulators have been developed in the last thirty years for different types of vehicles. Flight simulators and drive simulators are very well known examples. This paper describes the design and implementation of a dynamic simulator for the testing of inertial sensors devoted to vehicle navigation through a Hardware-In-The-Loop test rig composed of an industrial robot and a commercially available Inertial Measurement Unit (IMU). The authors are developing an innovative localization algorithm for railway vehicles which integrates inertial sensors with tachometers. The opportunity to set up a testing simulator capable of replicating in a realistic fashion the dynamic effects of the vehicle motion on inertial sensors allows to avoid expensive on board acquisitions and to speed up algorithm tuning. The real-time control architecture featured by the available industrial robot allows to precisely specify and execute motion trajectories with tight path and time law constraints required by the application at hand.
  • Automatic Data Driven Vegetation Modeling for Lidar Simulation Authors: Deschaud, Jean-Emmanuel; Prasser, David; Dias, M. Freddie; Browning, Brett; Rander, Peter
    Traditional lidar simulations render surface models to generate simulated range data. For objects with well-defined surfaces, this approach works well, and traditional 3D scene reconstruction algorithms can be employed to automatically generate the surface models. This approach breaks down, though, for many trees, tall grasses, and other objects with fine-scale geometry: surface models do not easily represent the geometry, and automated reconstruction from real data is difficult. In this paper, we introduce a new stochastic volumetric model that better captures the complexities of real lidar data of vegetation and is far better suited for automatic modeling of scenes from field collected lidar data. We also introduce several methods for automatic modeling and for simulating lidar data utilizing the new model. To measure the performance of the stochastic simulation we use histogram comparison metrics to quantify the differences between data produced by the real and simulated lidar. We evaluate our approach on a range of real world datasets and show improved fidelity for simulating geo-specific outdoor, vegetation scenes.
  • Simulation of Tactile Sensors Using Soft Contacts for Robot Grasping Applications Authors: Moisio, Sami; Leon, Beatriz; Korkealaakso, Pasi; Morales, Antonio
    In the context of robot grasping and manipulation, realistic simulation requires accurate modeling of contacts between bodies and, in a practical level, accurate simulation of touch sensors. This paper addresses the problem of simulating a tactile sensor considering soft contacts and full friction description. The developed model consists of a surface contact patch described by a mesh of contact elements. For each element, a full friction description is built considering stick-slip phenomena. The model is then implemented and used to perform typical tasks related to tactile sensors. The performance of the simulated sensor is then compared to a real one. It is also demonstrated how it can be integrated on the simulation of a complete robot grasping system.