TechTalks from event: Technical session talks from ICRA 2012

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Cable-Driven Mechanisms

  • Novel Equilibrium-Point Control of Agonist-Antagonist System with Pneumatic Artificial Muscles Authors: Ariga, Yohei; Uemura, Mitsunori; Hirai, Hiroaki; Miyazaki, Fumio
    This paper presents a novel method for controlling a single-joint robot arm driven by two pneumatic artificial muscles (PAMs). We introduce the concepts of the agonist-antagonist muscle-pairs ratio (A-A ratio) and the agonist-antagonist muscle-pairs activity (A-A activity), and demonstrate that our concepts enable separate linear control of the equilibrium joint angle and joint stiffness. We also discuss our approach in comparison with the equilibrium-point (EP) hypothesis.
  • Dynamic Trajectory Planning of a Two-DOF Cable-Suspended Parallel Robot Authors: Gosselin, Clement; Ren, Ping
    This paper presents a trajectory planning approach for cable-suspended parallel mechanisms. A planar two-degree-of-freedom parallel mechanism is used for the analysis. Based on the dynamic model of the suspended robot, a set of algebraic inequalities is obtained that represents the constraints on the cable tensions. Parametric Cartesian trajectories are then defined and substituted into the constraints in order to obtain global conditions on the trajectory parameters which ensure that the trajectories are feasible. Special frequencies arise from the equations that are akin to natural frequencies of pendulum-type systems. An experimental validation is also presented using a two-dof prototype. The proposed trajectory planning approach can be used to plan dynamic trajectories that go beyond the static workspace of the mechanism, thereby opening novel applications and possibilities for cable-suspended robots.
  • Force-Closure of Spring-Loaded Cable-Driven Open Chains: Minimum Number of Cables Required & Influence of Spring Placements Authors: Mustafa, Shabbir Kurbanhusen; Agrawal, Sunil
    While cable-driven systems offer the advantages of being lightweight with low moving inertia, the unilateral driving property of cables generally require them to have a greater number of actuators than their rigid-linked counterparts. This paper investigates the use of springs in an attempt to reduce the number of cables required. Given an n-DOF spring-loaded cable-driven open chain, several important questions arise: (i) How can force-closure analysis be carried out for a given spring and cable routing configuration? (ii) Are n+1 cables still necessary to fully constrain the entire open chain? (iii) What is the influence of spring placement on force-closure and cable tension required? This paper will address these concerns by proposing a systematic approach based on reciprocal screw theory. The analysis shows that an n-DOF spring-loaded cable driven open chain still requires a minimum of n+1 cables to fully constrain it. From preliminary analysis, spring placement can have a positive effect on altering the cable tension required and increasing the feasible workspace.
  • Development of a MR-Compatible Cable-Driven Manipulator: Design and Technological Issues Authors: Abdelaziz, Salih; Esteveny, Laure; Barbé, laurent; Renaud, Pierre; Bayle, Bernard; de Mathelin, Michel
    In this paper, we focus on the technology issues to be solved to develop a cable-driven robot compatible with Magnetic Resonance Imaging constraints. This study is based on the design of a new compact cable-driven manipulator with remote actuators, initially developed for prostate interventions. One of the originalities of the system is to use an instrumented structure to evaluate the cable tensions and lengths in order to perform an adequate control. The sensors assessment has been experimentally achieved and the necessity to introduce a new control strategy using the developed sensors has been demonstrated.
  • Application of Unscented Kalman Filter to a Cable Driven Surgical Robot: A Simulation Study Authors: Ramadurai, Srikrishnan; Nia Kosari, Sina; King, H. Hawkeye; Chizeck, Howard; Hannaford, Blake
    Cable driven power transmissions are used in applications such as haptic devices, surgical robots etc. The use of flexible cable based power transmission often causes relative motion between the motor actuator and mechanism joint during operation due to the elasticity of the cable.State-space control methods can be used to improve performance, but may require state estimates. For nonlinear systems, the Unscented Kalman Filter (UKF) provides a computationally efficient way to obtain state estimates. The UKF is applied here to a simulation of a minimially invasive surgical robot, to study the state estimation for a cable driven system with non-linear dynamics. State estimates from the UKF are compared with the known states available from the simulation. These state estimates are also utilized by two different controllers interacting with the simulation to test the UKF performance under closed loop control. We tested the UKF performance with error perturbations in the system model's cable stiffness parameter.
  • Joint Control of Tendon-Driven Mechanisms with Branching Tendons Authors: Sawada, Daisuke; Ozawa, Ryuta
    This paper proposes a joint control method for tendon-driven mechanisms (TDMs) with branching tendons that are connected to multiple tendons at a point, and which are often found in musculoskeletal systems. TDMs usually require the same number of tendons as actuators, which are one of the heaviest components in a robotics system. The utilization of branching tendons is useful for reducing the number of actuators needed for making lightweight robotic mechanisms, such as prosthetic hands. However, the under-actuation of the branching tendons makes it difficult to accurately control the joint motion of TDMs. Therefore, TDMs with branching tendons have been used only for simple adaptive grasping mechanisms. In this paper, we derive the tendon kinematics of TDMs with branching tendons and design a joint PD controller for the mechanisms. We demonstrate the stability of the control system using Lyapunov's direct method. We show that the bias force setting, which does not appear in conventional TDMs, is important in the realization of accurate control in TDMs with branching tendons. Simulations were performed to evaluate the proposed method.

Parallel Robots

  • Simplified Static Analysis of Large-Dimension Parallel Cable-Driven Robots Authors: Gouttefarde, Marc; Collard, Jean-François; Riehl, Nicolas; Baradat, Cédric
    This paper introduces a new simplified static analysis of parallel robots driven by inextensible cables of non-negligible mass. It is based on a known hefty cable static modeling which seems to have been overlooked in previous works on parallel cable-driven robots. This cable modeling is obtained from a well-known sagging cable modeling, known as the catenary, by assuming that cable sag is relatively small. The use of the catenary has been shown to lead to a non-linear set of equations describing the kinetostatic behavior of parallel robots driven by cables of non-negligible mass. On the contrary, the proposed simplified static analysis yields a linear relationship between (components of) the forces in the cables and the external wrench applied to the robot mobile platform. As a consequence, by means of the simplified static analysis, useful wrench-based analysis and design techniques devised for parallel robots driven by massless cables can now be extended to cases in which cable mass is to be accounted for.
  • Design Optimization for Parallel Mechanism Using on Human Hip Joint Power Assisting Based on Manipulability Inclusive Principle Authors: Yu, Yong; LIANG, WenYuan
    This paper summarizes the design optimization of a parallel mechanism using on human hip joint power assisting. Manipulability Inclusive Principle (MIP) evaluation criterion for evaluating assisting mechanism's assisting feasibility and assisting effect is proposed. The design of parallel assisting mechanism and building kinematical Jacobian are discussed. Moreover, as an important part of this paper, in order to finding out a architecture, which can satisfy assisting feasibility and realize higher assisting efficiency, more assisting ability and better feature on assisting isotropy, design optimization MIP is shown in this paper.
  • The Kinematics of the Redundant $N-1$ Wire Driven Parallel Robot Authors: Merlet, Jean-Pierre
    We address the kinematics of the redundant N-1 wire-driven parallel robot, i.e. a robot with N > 3 wires connected at the same point on the platform. The redundancy allows one to increase the workspace size. But we show, both theoretically and experimentally that if the wires are not elastic, then the redundancy cannot be used to control the wire tensions. Indeed we show that whatever are the number of wires there will always be only at most 3 wires in tension, while the other N-3 wires will be slack. We then show that if the wires are elastic, then the platform positioning will be very sensitive to stiffness identification and wire lengths control. Hence classical redundant control schemes are difficult to use for such robot and alternate use of the geometry of redundant wires have to be considered.
  • Error Modeling and Accuracy Analysis of a Multi-Level Hybrid Support Robot Authors: Chai, Xiaoming; Tang, Xiaoqiang; Tang, Lewei; Lu, Qiujian
    As for the multi-level hybrid feed support robot in the Five-hundred-meter Aperture Spherical radio Telescope (FAST), the cabin's time-varying barycenter and structural deformation are main factors causing the terminal receivers’ pose error. In order to ensure tracking accuracy of astronomical observations, firstly the elasticity model of the cable-driven Stewart manipulator is deduced to analyze the terminal error caused by the gravity torque. Newton-Raphson method is adopted to acquire the terminal error range and propose compensation strategy. Then error model considering structural deformation is formulated and the terminal accuracy is analyzed with an improved set theory based method. Finally the sensitivity analysis is also carried out and accuracy synthesis is implemented. Error modeling and analysis method proposed for the support robot in this paper can also be used to other complex hybrid robots with either large dimension or heavy duty.
  • Point-To-Point Motion Planning of a Parallel 3-DOF Underactuated Cable-Suspended Robot Authors: Zoso, Nathaniel; Gosselin, Clement
    This paper presents a planar parallel three-degree-of-freedom underactuated cable-driven robot. The mechanism is first described and a dynamic model is derived. One of the advantages of the proposed mechanism is that it does not require any mechanical (e.g. pulleys) or electrical (e.g. actuators) hardware to be mounted on the end-effector. A trajectory planning approach is developed, which is based on the natural frequency of the pendulum-like free motion (unconstrained degree of freedom). Sine-like excitation functions are used and their frequency and phase delay are determined using simulation results. A prototype is then described and experimental results are provided together with a video clip of an example trajectory. The results confirm that the mechanism can be effectively used for point-to-point trajectories.

Visual Tracking

  • Generic Realtime Kernel Based Tracking Authors: Hadj-Abdelkader, Hicham; Mezouar, Youcef; Chateau, Thierry
    This paper deals with the design of a generic visual tracking algorithm suitable for a large class of camera (single viewpoint sensors). It is based on the estimation of the relationship between observations and motion on the sphere. This is efficiently achieved using a kernel-based regression function on a generic linearly-weighted sum of non-linear basis functions. We also present two set of experiments. The first one shows the efficiency of our algorithm through the tracking in video sequences acquired with three types of cameras (conventional, dioptric-fisheye and catadioptric). The real-time performances will be shown by tracking one or several planes. The second set of experiments presents an application of our tracking algorithm to visual servoing with a fisheye camera.
  • Generative Object Detection and Tracking in 3D Range Data Authors: Kaestner, Ralf; Maye, Jerome; Pilat, Yves; Siegwart, Roland
    This paper presents a novel approach to tracking dynamic objects in 3D range data. Its key contribution lies in the generative object detection algorithm which allows the tracker to robustly extract objects of varying sizes and shapes from the observations. In contrast to tracking methods using discriminative detectors, we are thus able to generalize over a wide range of object classes matching our assumptions. Whilst the generative model underlying our framework inherently scales with the complexity and the noise characteristics of the environment, all parameters involved in the detection process obey a clean probabilistic interpretation. Nevertheless, our unsupervised object detection and tracking algorithm achieves real-time performance, even in highly dynamic scenarios covering a significant amount of moving objects. Through an application to populated urban settings, we are able to show that the tracking performance of the presented approach yields results which are comparable to state-of-the-art discriminative methods.
  • Moving Vehicle Detection and Tracking in Unstructured Environments Authors: Wojke, Nicolai; Häselich, Marcel
    The detection and tracking of moving vehicles is a necessity for collision-free navigation. In natural unstructured environments, motion-based detection is challenging due to low signal to noise ratio. This paper describes our approach for a 14 km/h fast autonomous outdoor robot that is equipped with a Velodyne HDL-64E S2 for environment perception. We extend existing work that has proven reliable in urban environments. To overcome the unavailability of road network information for background separation, we introduce a foreground model that incorporates geometric as well as temporal cues. Local shape estimates successfully guide vehicle localization. Extensive evaluation shows that the system works reliable and efficient in various outdoor scenarios without any prior knowledge about the road network. Experiments with our own sensor as well as on publicly available data from the DARPA Urban Challenge revealed more than 96 % correctly identified vehicles.
  • Learning to Place New Objects Authors: Jiang, Yun; Zheng, Changxi; Lim, Marcus; Saxena, Ashutosh
    The ability to place objects in an environment is an important skill for a personal robot. An object should not only be placed stably, but should also be placed in its preferred location/orientation. For instance, it is preferred that a plate be inserted vertically into the slot of a dish-rack as compared to being placed horizontally in it. Unstructured environments such as homes have a large variety of object types as well as of placing areas. Therefore our algorithms should be able to handle placing new object types and new placing areas. These reasons make placing a challenging manipulation task. In this work, we propose using a supervised learning approach for finding good placements given point-clouds of the object and the placing area. Our method combines the features that capture support, stability and preferred configurations, and uses a shared sparsity structure in its the parameters. Even when neither the object nor the placing area is seen previously in the training set, our learning algorithm predicts good placements. In robotic experiments, our method enables the robot to stably place known objects with a 98% success rate and 98% when also considering semantically preferred orientations. In the case of placing a new object into a new placing area, the success rate is 82% and 72%.
  • Lost in Translation (and Rotation): Rapid Extrinsic Calibration for 2D and 3D LIDARs Authors: Maddern, William; Harrison, Alastair; Newman, Paul
    This paper describes a novel method for determining the extrinsic calibration parameters between 2D and 3D LIDAR sensors with respect to a vehicle base frame. To recover the calibration parameters we attempt to optimize the quality of a 3D point cloud produced by the vehicle as it traverses an unknown, unmodified environment. The point cloud quality metric is derived from Rényi Quadratic Entropy and quantifies the compactness of the point distribution using only a single tuning parameter. We also present a fast approximate method to reduce the computational requirements of the entropy evaluation, allowing unsupervised calibration in vast environments with millions of points. The algorithm is analyzed using real world data gathered in many locations, showing robust calibration performance and substantial speed improvements from the approximations.