TechTalks from event: Technical session talks from ICRA 2012

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3D Surface Models, Point Cloud Processing

  • A Semi-Local Method for Iterative Depth-Map Refinement Authors: McKinnon, David; Smith, Ryan N.; Upcroft, Ben
    Building a photorealistic, 3D model of an object or a complete scene from image-based methods is a fundamental problem in computer vision, and has many applications in robotic perception, navigation, exploration and mapping. In this paper, we extend current state-of-the-art in the computation of depth maps by presenting an accurate and computationally efficient iterative hierarchical algorithm for multi-view stereo. The algorithm is designed to utilise all available contextual information to compute highly-accurate and robust depth maps by iteratively examining different image resolutions in an image-pyramid. The novelty in our approach is that we are able to incrementally improve the depth fidelity as the algorithm progresses through the image pyramid by utilising a local method. This is achieved in a computationally efficient manner by simultaneously enforcing the consistency of the depth-map by continual comparison with neighbouring depth-maps. We present a detailed description of the algorithm, and describe how each step is carried out. The proposed technique is used to analyse multi-view stereo data from two well-known, standard datasets, and presented results show a significant decrease in computation time, as well as an increase in overall accuracy of the computed depth maps.
  • Convex Bricks: A New Primitive for Visual Hull Modeling and Reconstruction Authors: Chari, Visesh; Agrawal, Amit; Taguchi, Yuichi; Ramalingam, Srikumar
    Industrial automation tasks typically require a 3D model of the object for robotic manipulation. The ability to reconstruct the 3D model using a sample object is useful when CAD models are not available. For textureless objects, visual hull of the object obtained using silhouette-based reconstruction can avoid expensive 3D scanners for 3D modeling. We propose convex brick (CB), a new 3D primitive for modeling and reconstructing a visual hull from silhouettes. CB's are powerful in modeling arbitrary non-convex 3D shapes. Using CB, we describe an algorithm to generate a polyhedral visual hull from polygonal silhouettes; the visual hull is reconstructed as a combination of 3D convex bricks. Our approach uses well-studied geometric operations such as 2D convex decomposition and intersection of 3D convex cones using linear programming. The shape of CB can adapt to the given silhouettes, thereby significantly reducing the number of primitives required for a volumetric representation. Our framework allows easy control of reconstruction parameters such as accuracy and the number of required primitives. We present an extensive analysis of our algorithm and show visual hull reconstruction on challenging real datasets consisting of highly non-convex shapes. We also show real results on pose estimation of an industrial part in a bin-picking system using the reconstructed visual hull.
  • Real-Time Compression of Point Cloud Streams Authors: Kammerl, Julius; Blodow, Nico; Rusu, Radu Bogdan; Gedikli, Suat; Beetz, Michael; Steinbach, Eckehard
    We present a novel lossy compression approach for point cloud streams which exploits spatial and temporal redundancy within the point data. Our proposed compression framework can handle general point cloud streams of arbitrary and varying size, point order and point density. Furthermore, it allows for controlling coding complexity and coding precision. To compress the point clouds, we perform a spatial decomposition based on octree data structures. Additionally, we present a technique for comparing the octree data structures of consecutive point clouds. By encoding their structural differences, we can successively extend the point clouds at the decoder. In this way, we are able to detect and remove temporal redundancy from the point cloud data stream. Our experimental results show a strong compression performance of a ratio of 14 at 1 mm coordinate precision and up to 40 at a coordinate precision of 9 mm.
  • Point Cloud Segmentation with LIDAR Reflection Intensity Behavior Authors: Tatoglu, Akin; Pochiraju, Kishore
    Light Detection and Ranging (LIDAR) scans are increasingly being used for 3D map construction and reverse engineering. The utility and benefit of the processed data maybe enhanced if the objects and geometry of the area scanned can be segmented and labeled. In this paper, we present techniques to model the intensity of the laser reflection return from a point during LIDAR scanning to determine diffuse and specular reflection properties of the scanned surface. Using several illumination models, the reflection properties of the surface are characterized by Lambertian diffuse reflection model and Phong, Gaussian and Beckmann specular models. Experimental set up with eight different surfaces with varied textures and glossiness enabled measurement of algorithm performance. Examples of point cloud segmentation with the presented approach are presented.

Needle Steering

  • A New Hand-Held Force-Amplifying Device for Micromanipulation Authors: Payne, Christopher; Tun Latt, Win; Yang, Guang-Zhong
    Abstract— This paper presents a new hand-held device capable of amplifying delicate micromanipulation forces during minimal invasive surgical tasks. It relays force sensing to the user through a simple sliding feature that is coupled to the surgical tool, which translates relative to the casing of the device held by the operator. This forgoes the need of grounding frames or anchoring mechanisms to the body, allowing the device to be used in general surgical environments without affecting the workflow. The device uses a three-phase linear motor that is compact and capable of generating high forces that allow amplification factors of up to ×15. It features a closed-loop force control scheme to perform the required force amplification in which the force exerted on to the user is measured, forming the feedback in the control loop. The device permits interchangeability of instrumentation through a simple docking feature, and thus can be generalized to a range of surgical instruments for micromanipulation tasks. Detailed bench test and user trials have been performed to validate the accuracy and practical performance of the device. The results have shown a five times reduction of the minimum force threshold perceived by the subjects and ergonomically sound manipulation advantages.
  • An Optical Actuation System and Curvature Sensor for a MR-Compatible Active Needle Authors: Ryu, Seok Chang; Quek, Zhan Fan; Renaud, Pierre; Black, Richard J.; Daniel, Bruce; Cutkosky, Mark
    A side optical actuation method is presented for a slender MR-compatible active needle. The needle includes an active region with a shape memory alloy (SMA) wire actuator, where the wire generates a contraction force when optically heated by a laser delivered though optical fibers, producing needle tip bending. A prototype, with multiple side heating spots, demonstrates twice as fast an initial response compared to fiber tip heating when 0.8 W of optical power is applied. A single-ended optical sensor with a gold reflector is also presented to measure the curvature independently of temperature as a function of optical transmission loss. Preliminary tests with the sensor prototype demonstrate approximately linear response and a repeatable signal, independent of the bending history.
  • Semi-automatic needle steering system with robotic manipulator Authors: Bernardes, Mariana Costa; Adorno, Bruno Vilhena; Poignet, Philippe; Borges, Geovany Araujo
    This paper presents a semi-automatic system for robotically assisted 2D needle steering that uses duty-cycling to perform insertions with arcs of adjustable curvature radius. It combines image feedback manually provided by an operator with an adaptive path planning strategy to compensate for system uncertainties and changes in the workspace during the procedure. Experimental results are presented to validate the proposed platform.
  • Torsional Dynamics Compensation Enhances Robotic Control of Tip-Steerable Needles Authors: Swensen, John; Cowan, Noah J.
    Needle insertions serve a critical role in a wide variety of medical interventions. Steerable needles provide a means by which to enhance existing percutaneous procedures and afford the development of entirely new ones. Here, we present a new time-varying model for the torsional dynamics of a steerable needle, along with a new controller that takes advantage of the model. The torsional model incorporates time-varying mode shapes to capture the changing boundary conditions caused during insertion of the needle into the tissue. Extensive simulations demonstrate the improvement over a model that neglects torsional dynamics, and illustrates the possible effect of torsional model order on efficacy. Pilot feedback control experiments, conducted in artificial tissue (plastisol) under stereo image guidance, validate the overall approach: our results substantially out-perform previously reported experimental results on controlling tip-steerable needles.
  • The Impact of Interaction Model on Stability and Transparency in Bilateral Teleoperation for Medical Applications Authors: Sanchez Secades, Luis Alonso; LE, Minh-Quyen; Liu, Chao; Zemiti, Nabil; Poignet, Philippe
    An analysis of stability and transparency of a force feedback teleoperation system for cutting-edge robotic surgery is presented. Previous works in teleoperated robotic surgery do not consider the real behavior of the environment, which was supposed to be only elastic. However, new surgical procedures in which the environment dynamics plays a crucial role start emerging as a result of technological progress. In robotic assisted beating-heart surgery, for instance, the dynamics of the contact between surgical tools and soft tissues has an impact not only in the performance of the force control task but also in the performance of the teleoperation control scheme in terms of transparency and stability. Therefore, a more realistic description of the environment has to be adopted in order to safely operate during robot-patient interaction. For this purpose, a viscoelastic contact model is introduced into the bilateral teleoperation scheme, and a performance study is provided. The obtained results show the advantages of the selected approach when targeting teleoperated surgical interventions in which the interaction dynamics has become a significant issue.

Networked Robots

  • Compensation of Packet Loss for a Network-Based Rehabilitation System Authors: Bae, Joonbum; Zhang, Wenlong; Tomizuka, Masayoshi
    In this paper, a network-based rehabilitation system is proposed to increase mobility of a rehabilitation system and to enable tele-rehabilitation. Control algorithms and rehabilitation strategies distributed at the central location (physical therapist) and the local site (patient) communicate over wireless network to realize a network-based rehabilitation system. To deal with possible packet losses over wireless network, a modified linear quadratic Gaussian (LQG) controller and a disturbance observer (DOB) are applied. The performance of the proposed system and control algorithms is verified by simulation and experiment with an actual knee rehabilitation system. The simulation and experiment results show that the network-based rehabilitation system with the proposed control schemes can generate the desired assistive torque accurately in presence of packet losses.
  • Motion Planning for Robust Wireless Networking Authors: Fink, Jonathan; Ribeiro, Alejandro; Kumar, Vijay
    We propose an architecture and algorithms for maintaining end-to-end network connectivity for autonomous teams of robots. By adopting stochastic models of point-to-point wireless communication and computing robust solutions to the network routing problem, we ensure reliable connectivity during robot movement in complex environments. We fully integrate the solution to network routing with the choice of node positions through the use of randomized motion planning techniques. Experiments demonstrate that our method succeeds in navigating a complex environment while ensuring that end-to-end communication rates meet or exceed prescribed values within a target failure tolerance.
  • Decentralised Information Gathering with Communication Costs Authors: Kassir, Abdallah; Fitch, Robert; Sukkarieh, Salah
    Advantages of decentralised decision making systems for multi-agent robotic tasks are limited by the heavy demand they impose on communication. This paper presents an approach to control communication for the LQ team problem, namely a team of agents with linear dynamics and quadratic team cost. Communication costs are added to the objective of the LQ optimal control linear matrix inequality formulation, allowing for a well-defined balancing of communication costs and team performance. Results show a reduction in communication consistent with the specified cost and in a manner that upholds team performance relative to the reduced communication footprint. The applicability of the approach has also been extended to information gathering tasks through local LQ approximations along the agents’ paths. Simulation testing on a sample two-agent problem shows a 40% reduction in communication with negligible impact on performance.
  • Decentralized Connectivity Maintenance for Networked Lagrangian Dynamical Systems Authors: Sabattini, Lorenzo; Secchi, Cristian; Chopra, Nikhil
    In order to accomplish cooperative tasks, multi-robot systems are required to communicate among each other. Thus, maintaining the connectivity of the communication graph is a fundamental issue. Connectivity maintenance has been extensively studied in the last few years, but generally considering only kinematic agents. In this paper we will introduce a control strategy that, exploiting a decentralized procedure for the estimation of the algebraic connectivity of the graph, ensures the connectivity maintenance for groups of Lagrangian systems. The control strategy is validated by means of analytical proofs and simulation results.
  • Multi-Target Tracking Using Distributed SVM Training Over Wireless Sensor Networks Authors: Kim, Woojin; YOO, Jae Hyun; Kim, H. Jin
    In this paper, we propose to use distributed support vector machine (SVM) training to solve a multi-target tracking problem in wireless sensor networks. We employ gossip-based incremental SVM to obtain the discriminant function. By gossiping the support vectors with neighboring sensor nodes, the local SVM training results can achieve the agreement of the sub-optimal discriminant planes. After training the local SVM at each node, we can calculate the posterior probability of the existence of the targets using Platt's method. By maximum a posterior (MAP), the target trajectories are estimated. In order to validate the proposed tracking framework in wireless sensor networks, we perform two different target-tracking experiments. The experimental results demonstrate that the proposed procedure provides a good estimator, and supports the feasibility of applying the distributed SVM training to the target tracking problems.
  • A Dual-Use Visible Light Approach to Integrated Communication and Localization of Underwater Robots with Application to Non-Destructive Nuclear Reactor Inspection Authors: Rust, Ian; Asada, Harry
    Visible light communication systems have gained prominence as a method for wireless underwater communications. This is because these systems are capable of long distance communications in water with high bandwidths. A requirement of visible light systems, however, is consistent line of sight to maintain a communication link. This arises from the directional nature of visible light emitters and detectors. One solution to this problem is to implement feedback control in order to “point” visible light emitters and detectors at one another. This in turn requires precise estimation of the relative locations of these two components as a feedback signal. In this work, a system is presented that uses the modulated light signal both as a medium with which to carry data and as a reference upon which to base the localization of a mobile robot. This is therefore a dual-use system, for both communication and localization. First, this paper presents the architecture of a dual-use visible light communication and localization system. The localization is carried out using an Extended Kalman Filter (EKF) algorithm. Then, a planar version of this dual-use system is tested, demonstrating the feasibility and effectiveness of the dual-use approach.