TechTalks from event: Technical session talks from ICRA 2012

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Force & Tactile Sensors

  • Finger Flexion Force Sensor Based on Volar Displacement of Flexor Tendon Authors: Heo, Pilwon; Kim, Jung
    A wearable sensor for measuring finger flexion force based on volar displacement of flexor tendon is presented. The proposed sensor utilizes a principle that the volar displacement of tendon under a pulley depends on both of tendon tension and finger posture when a external compressive force is applied on the pulley. A prototype sensor is built for the verification of the proposed method. Experiments with isometric conditions are performed in 9 different finger postures to observe the response of the sensor with regard to the finger flexion force and finger posture. The results show that the output of the proposed sensor has dependency on both of finger force and posture. This implies that the sensor can be used for measuring finger flexion force when the finger posture and the corresponding sensor response is known. A simulation with simplified model is performed to explain the behavior of the sensor output.
  • A Compact Two DOF Magneto-Elastomeric Force Sensor for a Running Quadruped Authors: Ananthanarayanan, Arvind; Foong, Shaohui; Kim, Sangbae
    This paper presents a novel design approach for a two-DOF foot force sensor for a high speed running quadruped. The adopted approach harnesses the deformation property of an elastomeric material to relate applied force to measurable deformation. A lightweight, robust and compact magnetic-field based sensing system, consisting of an assembly of miniature hall-effect sensors, is employed to infer the positional information of a magnet embedded in the elastomeric material. Instead of solving two non-linear models (magnetic field and elastomeric) sequentially, a direct approach of using artificial neural networks (ANN) is utilized to relate magnetic flux density (MFD) measurements to applied forces. The force sensor, which weighs a only 24.5 gms, provides a measurement range of 0 - 1000 N normal to the ground and up to $pm$ 125N parallel to the ground. The mean force measurement accuracy was found to be within 7% of the applied forces. The sensor designed as part of this work finds direct applications in ground reaction force sensing for a running quadrupedal robot.
  • Basic Experiments of Three-Axis Tactile Sensor Using Optical Flow Authors: Ohka, Masahiro; Matsunaga, Takuya; Nojima, Yu; Noda, Daiji; Hattori, Tadashi
    Three-axis tactile sensing has advantages for grasping an object of unknown mass and hardness. We developed a new three-axis tactile sensor that possesses a simple structure to endure large applied force from a powerful grasp. Vertical force distribution is measured based on grayscale values obtained by image data processing, as with previous three-axis tactile sensors. Tangential force distribution is determined by the linear movement of image data calculated by optical flow. The sensing characteristics of this sensor are dominated by the configuration and material of fine conical feelers formed on a silicon rubber sheet. By UV-LIGA, we obtain a fine mold of a silicon rubber sheet. In evaluation experiments, we applied both vertical and tangential force to the sensor and confirmed this tactile sensor’s ability to acquire normal and tangential forces. In its design, we utilize a USB microscope that has a CMOS camera and a light source. In a series of experiments, we performed vertical and tangential force tests to obtain its basic characteristics. The linear relationship between the grayscale value and the vertical force is obtained from the vertical force test. If the average optical flow is under 0.2 mm, the tangential force is proportional to the average optical flow. The inclination of the relationship between the tangential force and the average optical flow increases with additional vertical force. Finally, we derive a series of equations for three-axis force calculatio
  • A Computationally Fast Algorithm for Local Contact Shape and Pose Classification Using a Tactile Array Sensor Authors: Liu, Hongbin; Song, Xiaojing; Nanayakkara, Thrishantha; Seneviratne, lakmal; Althoefer, Kaspar
    This paper proposes a new computationally fast algorithm for classifying the primitive shape and pose of the local contact area in real-time using a tactile array sensor attached on a robotic fingertip. The proposed approach abstracts the lower structural property of the tactile image by analyzing the covariance between pressure values and their locations on the sensor and identifies three orthogonal principal axes of the pressure distribution. Classifying contact shapes based on the principal axes allows the results to be invariant to the rotation of the contact shape. A naïve Bayes classifier is implemented to classify the shape and pose of the local contact shapes. Using an off-shelf low resolution tactile array sensor which comprises of 5×9 pressure elements, an overall accuracy of 97.5% has been achieved in classifying six primitive contact shapes. The proposed method is very computational efficient (total classifying time for a local contact shape = 576μs (1736 Hz)). The test results demonstrate that the proposed method is practical to be implemented on robotic hands equipped with tactile array sensors for conducting manipulation tasks where real-time classification is essential.
  • Analysis of the Trade-Off between Resolution and Bandwidth for a Nanoforce Sensor Based on Diamagnetic Levitation Authors: Piat, Emmanuel; Abadie, Joel; OSTER, Stéphane
    Nanoforce sensors based on passive diamagnetic levitation with a macroscopic seismic mass are a possible alternative to classical Atomic Force Microscopes when the force bandwidth to be measured is limited to a few Hertz. When an external unknown force is applied to the levitating seismic mass, this one acts as a transducer that converts this unknown input into a displacement that is the measured output signal. Because the inertia effect due to the mass of such macroscopic transducers can not be neglected for timevarying force measurement, it is necessary to deconvolve the displacement to correctly estimate the unknown input force. A deconvolution approach based on a Kalman filter and controlled by a scalar parameter has been recently proposed. The adjustement of this parameter leads to a trade-off that is analysed in this paper in term of resolution and bandwidth of the estimated force. Associated tools to help the end-user to set this parameter are also described.
  • An Investigation of the Use of Linear Polarizers to Measure Force and Torque in Optical 6-DOF Force/Torque Sensors for Dexterous Manipulators Authors: Sargeant, Ramon; Seneviratne, lakmal; Althoefer, Kaspar
    This paper presents a prototype of a force/torque sensor that uses fiber optic guided light and linear polarizer materials to obtain intensity modulated light to detect applied force and torque to the sensing structure. The sensor is also capable of measuring the contact direction between the sensor and the object. The sensor’s design and operating principles are explained and experimental data is given to verify the proposed operating principle. The experimental data shows that linear polarizers can be used to measure the torque applied to a force/torque sensor.

Motion Path Planning I

  • Navigation Functions for Everywhere Partially Sufficiently Curved Worlds Authors: Filippidis, Ioannis; Kyriakopoulos, Kostas
    We extend Navigation Functions (NF) to worlds of more general geometry and topology. This is achieved without the need for diffeomorphisms, by direct definition in the geometrically complicated configuration space. Every obstacle boundary point should be partially sufficiently curved. This requires that at least one principal normal curvature be sufficient. A normal curvature is termed sufficient when the tangent sphere with diameter the associated curvature radius is a subset of the obstacle. Examples include ellipses with bounded eccentricity, tori, cylinders, one-sheet hyperboloids and others. Our proof establishes the existence of appropriate tuning for this purpose. Direct application to geometrically complicated cases is illustrated through nontrivial simulations.
  • Trajectory Tracking among Landmarks and Binary Sensor-Beams Authors: Tovar, Benjamin; Murphey, Todd
    We study a trajectory tracking problem for a mobile robot moving in the plane using combinatorial observations from the state. These combinatorial observations come from crossing binary detection beams. A binary detection beam is a sensing abstraction arising from physical sensor beams or virtual beams that are derived from several sensing modalities, such as actual detection beams in the environment, changes in the angular order of landmarks around the robot, or recognizable markings in the plane. We solve the filtering problem from a geometric perspective and present its relation to linear recursive filters in control theory. Subsequently, we develop the acceleration control of the robot to track a given input trajectory, with a finite control set consisting on moving toward landmarks naturally modeling the robot as a switched dynamical system. We present experiments using an e-puck differential-drive robot, in which a useful estimate of the state for tracking is produced regardless of nontrivial uncertainty.
  • A Singularity-Free Path Planner for Closed-Chain Manipulators Authors: Bohigas, Oriol; Henderson, Michael E.; Ros, Lluis; Porta, Josep M
    This paper provides an algorithm for computing singularity-free paths on non-redundant closed-chain manipulators. Given two non-singular configurations of the manipulator, the method attempts to connect them through a configuration space path that maintains a minimum clearance with respect to the singularity locus at all points. The method is resolution-complete, in the sense that it always returns a path if one exists at a given resolution, or returns "failure'' otherwise. The path is computed by defining a new manifold that maintains a one-to-one correspondence with the singularity-free configuration space of the manipulator, and then using a higher-dimensional continuation technique to explore this manifold systematically from one configuration, until the second configuration is found. Examples are included that demonstrate the performance of the method on illustrative situations.
  • Comparison of Constrained Geometric Approximation Strategies for Planar Information States Authors: Song, Yang; O'Kane, Jason
    This paper describes and analyzes a new technique for reasoning about uncertainty called constrained geometric approximation (CGA). We build upon recent work that has developed methods to explicitly represent a robot's knowledge as an element, called an information state, in an appropriately defined information space. The intuition of our new approach is to constrain the I-state to remain in a structured subset of the I-space, and to enforce that constraint using appropriate overapproximation methods. The result is a collection of algorithms that enable mobile robots with extreme limitations in both sensing and computation to maintain simple but provably meaningful representations of the incomplete information available to them. We present a simulated implementation of this technique for a sensor-based navigation task, along with experimental results for this task showing that CGA, compared to a high-fidelity representation of the un-approximated I-state, achieves a similar success rate at a small fraction of the computational cost.
  • Voxel-Based Motion Bounding and Workspace Estimation for Robotic Manipulators Authors: Anderson-Sprecher, Peter; Simmons, Reid
    Identification of regions in space that a robotic manipulator can reach in a given amount of time is important for many applications, such as safety monitoring of industrial manipulators and trajectory and task planning. However, due to the high-dimensional configuration space of many robots, reasoning about possible physical motion is often intractable. In this paper, we propose a novel method for creating a <i>reachability grid</i>, a voxel-based representation that estimates the minimum time needed for a manipulator to reach any physical location within its workspace. We use up to second-degree constraints on joint motion to model motion limits for each joint independently, followed by successive voxel approximations to map these limits on to the robot’s physical workspace. Results using a simulated manipulator indicate that our method can produce accurate reachability grids in real-time, even for robots with many degrees of freedom. Furthermore, errors are almost exclusively biased towards producing more optimistic reachability estimates, which is a desirable characteristic for many applications.
  • Branch and Bound for Informative Path Planning Authors: Binney, Jonathan; Sukhatme, Gaurav
    We present an optimal algorithm for informative path planning (IPP), using a branch and bound method inspired by feature selection algorithms. The algorithm uses the monotonicity of the objective function to give an objective function-dependent speedup versus brute force search. We present results which suggest that when maximizing variance reduction in a Gaussian process model, the speedup is significant.

Mobile Manipulation: Planning & Control

  • Planning with Adaptive Dimensionality for Mobile Manipulation Authors: Gochev, Kalin; Safonova, Alla; Likhachev, Maxim
    Mobile manipulation planning is a hard problem composed of multiple challenging sub-problems, some of which require searching through large high-dimensional state-spaces. The focus of this work is on computing a trajectory to safely maneuver an object through an environment, given the start and goal configurations. In this work we present a heuristic search-based deterministic mobile manipulation planner, based on our recently-developed algorithm for planning with adaptive dimensionality. Our planner demonstrates reasonable performance, while also providing strong guarantees on completeness and suboptimality bounds with respect to the graph representing the problem.
  • Unifying Perception, Estimation and Action for Mobile Manipulation Via Belief Space Planning Authors: Kaelbling, Leslie; Lozano-Perez, Tomas
    In this paper, we describe an integrated strategy for planning, perception, state-estimation and action in complex mobile manipulation domains. The strategy is based on planning in the belief space of probability distribution over states. Our planning approach is based on hierarchical symbolic regression (pre-image back-chaining). We develop a vocabulary of fluents that describe sets of belief states, which are goals and subgoals in the planning process. We show that a relatively small set of symbolic operators lead to task-oriented perception in support of the manipulation goals.
  • Distributed Cooperative Object Attitude Manipulation Authors: Markdahl, Johan; Karayiannidis, Yiannis; Hu, Xiaoming; Kragic, Danica
    This paper proposes a local information based control law in order to solve the planar manipulation problem of rotating a grasped rigid object to a desired orientation using multiple mobile manipulators. We adopt a multi-agent systems theory approach and assume that: (i) the manipulators (agents) are capable of sensing the relative position to their neighbors at discrete time instances, (ii) neighboring agents may exchange information at discrete time instances, and (iii) the communication topology is connected. Control of the manipulators is carried out at a kinematic level in continuous time and utilizes inverse kinematics. The mobile platforms are assigned trajectory tracking tasks that adjust the positions of the manipulator bases in order to avoid singular arm configurations. Our main result concerns the stability of the proposed control law.
  • A Hybrid Control for Automatic Docking of Electric Vehicles for Recharging Authors: Petrov, Plamen; Boussard, clément; Ammoun, Samer; Nashashibi, Fawzi
    In this paper, we present the architecture of an innovative docking station for electric vehicles recharging and a hybrid control scheme for automatic docking of the vehicles. This work is a part of on-going project concerning the development of a smart charging station for electric vehicles equipped with an automated arm, which connect the vehicle to the charging station, and an infrared beacon system for localizing the automatically maneuvering vehicle in the docking area. The proposed control scheme combines time-optimal (bang-bang) control with continuous time-invariant nonlinear control, which stabilizes the vehicle to a small neighborhood of the docking point. Simulation and experimental results illustrate the effectiveness of the proposed controller
  • On Continuous Null Space Projections for Torque-Based, Hierarchical, Multi-Objective Manipulation Authors: Dietrich, Alexander; Albu-Schäffer, Alin; Hirzinger, Gerd
    The technological progress in the field of robotics results in more and more complex manipulators. However, having an increasing number of degrees of freedom raises the question of how to use them effectively. In turn, establishing manipulators in human environments, e.g., as service robots, calls for the fulfillment of various constraints and tasks at the same time. In the context of torque controlled robotic systems, we provide an approach to simultaneously deal with a multitude of tasks and constraints which are arranged in a hierarchy, utilizing the large number of actuated joints of the manipulator. To this end, we propose a continuous null space projection technique to consider unilateral constraints, singular Jacobian matrices and dynamic variations of the priority order within the hierarchical structure. We show that activating and deactivating tasks as well as crossing singularities does not lead to a discontinuous control law. Simulations and experiments on the humanoid Justin of the German Aerospace Center (DLR) validate our approach. The presented concept is supposed to contribute to whole-body control frameworks.