TechTalks from event: Technical session talks from ICRA 2012

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Sensor Networks

  • Distributed Coverage with Mobile Robots on a Graph: Locational Optimization Authors: Yun, Seung-kook; Rus, Daniela
    This paper presents a decentralized algorithm for coverage with mobile robots on a graph. Coverage is an important capability of multi-robot systems engaged in a number of different applications, including placement for environmental modeling, deployment for maximal quality surveillance, and even coordinated construction.We use distributed vertex substitution for locational optimization, and the controllers minimize the corresponding cost function. We prove that the proposed controller with two-hop communication guarantees convergence to the locally optimal configuration. We evaluate the algorithms in simulations and compare them to the coverage algorithm in a continuous domain.
  • An Approach to Multi-Agent Area Protection Using Bayes Risk Authors: Bays, Matthew; Shende, Apoorva; Stilwell, Daniel
    We introduce a novel approach to controlling the motion of a team of agents so that they jointly minimize a cost function utilizing Bayes risk. We use a particle-based approach and approximations that allow us to express the optimization problem as a mixed-integer linear program. We illustrate this approach with an area protection problem in which a team of mobile agents must intercept mobile targets before the targets enter a specified area. Bayes risk is a useful measure of performance for applications where agents must perform a classification task. By minimizing Bayes risk, agents are able to explicitly account for the cost of incorrect classification. In our application, a team of mobile agents must classify potential mobile targets as threat or safe based on the likelihood the targets will enter the specified area. The agents must also maneuver to intercept targets that are classified as threat.
  • On Coordination in Practical Multi-Robot Patrol Authors: Agmon, Noa; Fok, Chien-Liang; Elmaliah, Yehuda; Stone, Peter; Julien, Christine; Vishwanath, Sriram
    Multi-robot patrol is a fundamental application of multi-robot systems. While much theoretical work exists providing an understanding of the optimal patrol strategy for teams of coordinated, homogeneous robots, little work exists on building and evaluating the performance of such systems in the real world. In this paper, we evaluate the performance of multi-robot patrol in a practical outdoor robotic system, and evaluate the effect of different coordination schemes on the performance of the robotic team, which is influenced by their communication capabilities and degree of heterogeneity. We specifically focus on frequency-based multi-robot patrol along a cyclic route specified by a set of GPS-waypoints. The multi-robot patrol algorithms evaluated vary in the level of coordination of the robots: no coordination, loose coordination, and strong coordination. In addition, we evaluate versions of these algorithms that distribute state information---either individual state, or state of the entire team (global state). Our experiments show that while strong coordination was theoretically proven to be optimal, in practice uncoordinated patrol performed better in terms of average waypoint visitation frequency. Furthermore, loosely coordinated patrol that shares only individual state outperformed all other coordination schemes in terms of worst-case frequency, and it performed significantly better than a loosely coordinated algorithm based on sharing global-view state. We respond t
  • Adaptive Sampling Using Mobile Sensor Networks Authors: Huang, Shuo; Tan, Jindong
    This paper presents an adaptive sparse sampling approach and the corresponding real-time scalar field reconstruction method using mobile sensor networks. Traditionally, the sampling methods collect measurements without considering possible distributions of target signals. A feedback driven algorithm is discussed in this paper, where new measurements are determined based on the analysis of existing observations. The information amount of each potential measurement is evaluated under a sparse domain based on compressive sensing framework given all existing information shared among networked mobile sensors, and the most informative one is selected. The efficiency of this information-driven method falls into the information maximization for each individual measurement. The simulation results show the efficacy and efficiency of this approach, where a scalar field is recovered.
  • Coverage Control of Mobile Sensors for Adaptive Search of Unknown Number of Targets Authors: Surana, Amit; Mathew, George; Kannan, Suresh
    We present a multiscale adaptive search algorithm for efficiently searching an unknown number of stationary targets using a team of multiple mobile sensors. We first derive a Spectral Multiscale Coverage (SMC) control law for a Dubins vehicle model. Given a search prior, the SMC control gives rise to uniform coverage dynamics for the mobile sensors such that the amount of time spent observing a region is proportional to finding a target in it. In order to make the search robust to sensor uncertainties and Automatic Target Detection algorithm errors (i.e. false alarm, missed detections), we combine the SMC control with decision and estimation theoretic techniques. As new targets are discovered we use the Sequential Ratio Probability Test and Recursive Least Squares estimation to quantify the current uncertainty in target detection and location, respectively. This uncertainty is used to update the search prior so as to balance exploitation (reduce uncertainty in state of already discovered potential targets) and exploration (discover new targets). We demonstrate this adaptive search methodology in a high fidelity simulation environment and show an improved performance over lawnmower type search.

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.