TechTalks from event: Technical session talks from ICRA 2012

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Calibration and Identification

  • Automatic Camera and Range Sensor Calibration using a single Shot Authors: Geiger, Andreas; Moosmann, Frank; Car, Ömer; Schuster, Bernhard
    As a core robotic and vision problem, camera and range sensor calibration have been researched intensely over the last decades. However, robotic research efforts still often get heavily delayed by the requirement of setting up a calibrated system consisting of multiple cameras and range measurement units. With regard to removing this burden, we present a toolbox with web interface for fully automatic camera-to-camera and camera-to-range calibration. Our system is easy to setup and recovers intrinsic and extrinsic camera parameters as well as the transformation between cameras and range sensors within one minute. In contrast to existing calibration approaches, which often require user intervention, the proposed method is robust to varying imaging conditions, fully automatic, and easy to use since a single image and range scan proves sufficient for most calibration scenarios. Experimentally, we demonstrate that the proposed checkerboard corner detector significantly outperforms current state-of-the-art. Furthermore, the proposed camera-to-range registration method is able to discover multiple solutions in the case of ambiguities. Experiments using a variety of sensors such as grayscale and color cameras, the Kinect 3D sensor and the Velodyne HDL-64 laser scanner show the robustness of our method in different indoor and outdoor settings and under various lighting conditions.
  • Scale-Only Visual Homing from an Omnidirectional Camera Authors: Pradalier, Cedric; Liu, Ming; Pomerleau, Francois; Siegwart, Roland
    Visual Homing is the process by which a mobile robot moves to a Home position using only information extracted from visual data. The approach we present in this paper uses image keypoints (e.g. SIFT) extracted from omnidirectional images and matches the current set of keypoints with the set recorded at the Home location. In this paper, we first formulate three different visual homing problems using uncalibrated omnidirectional camera within the Image Based Visual Servoing (IBVS) framework; then we propose a novel simplified homing approach, which is inspired by IBVS, based only on the scale information of the SIFT features, with its computational cost linear to the number of features. This paper reports on the application of our method on a commonly cited indoor database where it outperforms other approaches. We also briefly present results on a real robot and allude on the integration into a topological navigation framework.
  • 3D Monocular Robotic Ball Catching with an Iterative Trajectory Estimation Refinement Authors: Lippiello, Vincenzo; Ruggiero, Fabio
    In this paper, a 3D robotic ball catching algorithm which employs only an eye-in-hand monocular visual-system is presented. A partitioned visual servoing control is used in order to generate the robot motion, keeping always the ball in the field of view of the camera. When the ball is detected, the camera mounted on the robot end-effector is commanded to follow a suitable baseline in order to acquire measurements and provide a first possible interception point through a linear estimation process. Thereafter, further visual measures are acquired in order to continuously refine the previous prediction through a non-linear estimation process. Experimental results show the effectiveness of the proposed solution.
  • Automatically Calibrating the Viewing Direction of Optic-Flow Sensors Authors: Briod, Adrien; Zufferey, Jean-Christophe; Floreano, Dario
    Because of their low weight, cost and energy consumption, optic-flow sensors attract growing interest in robotics for tasks such as self-motion estimation or depth measurement. Most applications require a large number of these sensors, which involves a fair amount of calibration work for each setup. In particular, the viewing direction of each sensor has to be measured for proper operation. This task is often cumbersome and prone to errors, and has to be carried out every time the setup is slightly modified. This paper proposes an algorithm for viewing direction calibration relying on rate gyroscope readings and a recursive weighted linear least square estimation of the rotation matrix elements. %an iterative algorithm. The method only requires the user to realize random rotational motions of its setup by hand. The algorithm provides hints about the current precision of the estimation and what motions should be performed to improve it. To assess the validity of the method, tests were performed on an experimental setup and the results compared to a precise manual calibration. The repeatability of the gyroscope-based calibration process reached +-1.7° per axis.
  • An Analytical Least-Squares Solution to the Odometer-Camera Extrinsic Calibration Problem Authors: Guo, Chao; Mirzaei, Faraz; Roumeliotis, Stergios
    In order to fuse camera and odometer measurements, we first need to estimate their relative transformation through the so-called odometer-camera extrinsic calibration. In this paper, we present a two-step analytical least-squares solution for the extrinsic odometer-camera calibration that (i) is not iterative and finds the least-squares optimal solution without any initialization, and (ii) does not require any special hardware or the presence of known landmarks in the scene. Specifically, in the first step, we estimate a subset of the 3D relative rotation parameters by analytically minimizing a least-squares cost function. We then back-substitute these estimates in the measurement constraints, and determine the rest of the 3D transformation parameters by analytically minimizing a second least-squares cost function. Simulation and experimental results are presented to validate the efficiency of the proposed algorithm.
  • Online Calibration of Vehicle Powertrain and Pose Estimation Parameters Using Integrated Dynamics Authors: Seegmiller, Neal Andrew; Kelly, Alonzo; Rogers-Marcovitz, Forrest
    This paper presents an online approach to calibrating vehicle model parameters that uses the integrated dynamics of the system. Specifically, we describe the identification of the time constant and delay in a first-order model of the vehicle powertrain, as well as parameters required for pose estimation (including position offsets for the inertial measurement unit, steer angle sensor parameters, and wheel radius). Our approach does not require differentiation of state measurements like classical techniques; making it ideal when only low-frequency measurements are available. Experimental results on the LandTamer and Zoe rover platforms show online calibration using integrated dynamics to be fast and more accurate than both manual and classical calibration methods.

Compliant Nanopositioning

  • Compliances of Symmetric Flexure Hinges for Planar Compliant Mechanisms Authors: Lobontiu, Nicolae; Cullin, Matt; Ephrahim, Garcia; McFerran Brock, Jennifer; Ali, Muhammad
    A general analytical compliance model is presented for symmetric flexure hinges formed of serial segments of known compliances and with thicknesses defined analytically. Serial combination, mirroring, and translation of individual segments yield the flexure compliances. As an illustration, the compliances of a right elliptical corner-filleted flexure hinge are studied. For an aluminum sample with dimensions of l = 0.0254 m, a = 0.006 m, b = 0.008 m, t = 0.0015 m, and w = 0.00635 m, experimental testing, finite element simulation, and analytical results are very close. Results of this study include plots of the rotary compliance in terms of geometric parameters.
  • Flexure Design Using Metal Matrix Composite Materials: Nanopositioning Example Authors: Leang, Kam K.
    Advanced metal matrix composite (MMC) materials combine a metal and at least another part, such as a ceramic, to form a material with enhanced mechanical properties compared to traditional materials. An aluminium silicon carbide metal matrix material is investigated for compliant flexure design for nanopositioning systems. The material is up to 60% stiffer than traditional aluminum alloy with little to no increase in density. It is shown that the dynamic response of flexure-guided stages can be more easily tailored using the MMC. A flexure-based nanopositioner is designed to exhibit low cross-coupling behavior at high frequencies using the MMC. Finite element analysis (FEA) is used to guide the design process, and a prototype stage is created and evaluated. The measured dynamic response agrees with the FEA modeling; particularly, by using the MMC the actuation mode of the stage can be designed to occur before the out-of-plane modes. The improvement in performance of using the MMC outweighs the disadvantages that include increase cost of the material and lower manufacturability compared to traditional aluminum alloys. The stage is characterized to demonstrate the advantages of the material.
  • Using Frequency-Weighted Data Fusion to Improve the Performance of a Digital Charge Amplifier Authors: Bazghaleh, Mohsen; Grainger, Steven; Cazzolato, Benjamin Seth; Lu, Tien-Fu
    Piezoelectric actuators are the most common among a variety of smart actuators due to their high resolution, low power consumption and wide operating frequency but they suffer hysteresis which affects linearity. In this paper a novel digital charge amplifier is presented which reduces hysteresis and linearizes the piezoelectric actuator. A frequency-weighted data fusion algorithm uses a non-linear ARX model to remove drift and increase the bandwidth of digital charge amplifier. Experimental results are presented.
  • A Z-Scanner Design for High-Speed Scanning Probe Microscopy Authors: Yong, Yuen Kuan; Moheimani, S. O. Reza
    A major challenge in high-speed Atomic Force Microscopy is the low vertical bandwidth of the Z-scanner feedback loop. The maximum vertical feedback bandwidth is limited by the first Z-axis resonance frequency of the scanner. In this article, the design of a fast Z-scanner for high-speed Atomic Force Microscopy is presented. The Z-scanner consists of a piezoelectric stack actuator and a diaphragm flexure. The flexure provides the necessary preload to the actuator to prevent it from getting damaged during high-speed scans. A finite-element-analysis based optimization method is used to achieve a high resonance frequency of about 60 kHz. A counterbalance is added to the Z-scanner to minimize the inertial effect which tends to cause vibrations in the lateral axes of the device. This mechanical design enabled us to achieve a closed-loop vertical control bandwidth of 6.5 kHz. This is significantly higher than the closed loop bandwidth of the commercial AFM in which this stage was tested. AFM images of a test grating with sharp corners were recorded at a resolution of 200 x 200 pixels at 10 Hz, 100 Hz and 200 Hz line rates without noticeable image artifacts due to insufficient vertical bandwidth and vibrations.
  • Estimating the Resolution of Nanopositioning Systems from Frequency Domain Data Authors: Fleming, Andrew J.
    Mechanical and electrical noise in nanopositioning systems is unavoidable and dictates the maximum positioning resolution. The proper specification of resolution is critical for defining the smallest possible dimensions in a manufacturing processes or the smallest measurable features in an imaging application. This article defines a standard for the reporting of resolution and demonstrates how this parameter can be measured and predicted from frequency domain data.

Micro and Nano Robots I

  • Polymer-Based Wireless Resonant Magnetic Microrobots Authors: Tung, Hsi-Wen; Frutiger, Dominic R.; Pane, Salvador; Nelson, Bradley J.
    We present a class of Wireless Resonant Magnetic Microactuator (WRMMA) that integrates a polymer spring/body structure with electroplated ferromagnetic masses. The new devices, which we call PolyMites as they are derived from our previous MagMites, are simpler, faster and cheaper to fabricate than the MagMite. Like their predecessor, they are capable of moving on planar surfaces in dry and wet environments. Their improved biocompatibility also extends their potential for biological applications. PolyMites are 500 μm in diameter and 55 μm in height. In air they have attained a speed of 13 mm/s, approximately 26 body lengths per second. PolyMites are capable of micromanipulation on a surface, which is demonstrated by pushing and releasing micro-objects such as polystyrene beads in water.
  • Three-Dimensional Control of Engineered Motile Cellular Microrobots Authors: Kim, Dal Hyung; Kim, Paul; Julius, Agung; Kim, MinJun
    We demonstrate three-dimensional control with the eukaryotic cell Tetrahymena pyriformis (T. pyriformis) using two sets of Helmholtz coils for xy-plane motion and a single electromagnet for vertical motion. T. pyriformis is modified to have artificial magnetotaxis with internalized magnetite. Since the magnetic fields exerted by electromagnets are relatively uniform in the working space, the magnetite exerts only torque, without translational force, which enabled us to guide the cell’s swimming direction while the swimming force is exerted only by the cell’s motile organelles. A stronger magnetic force was necessary to steer cells to the z¬-axis, and, as a result, a single electromagnet placed just below our sample area is utilized for vertical motion. To track the cell’s positions in the z-axis, intensity profiles of non-motile cells at varying distances from the focal plane are used. During vertical motion along the z-axis, the intensity difference from the background decreases while the cell size increases. Since the cell is pear-shaped, the eccentricity is high during planar motion, but lowers during vertical motion due to the change in orientation. The three-dimensional control of the live organism T. pyriformis as a cellular robot shows great potential to be utilized for practical applications in microscale tasks, such as target transport and cell therapy.
  • Towards MR-Navigable Nanorobotic Carriers for Drug Delivery into the Brain Authors: Tabatabaei, Seyed Nasrollah; Sonia, Duchemin; Giouard, Hélène; Martel, Sylvain
    Magnetic Resonance Navigation (MRN) relies on Magnetic Nanoparticles (MNPs) embedded in microcarriers or microrobots to allow the induction of a directional propelling force by 3D magnetic gradients. These magnetic gradients are superposed on a sufficiently high homogeneous magnetic field to achieve maximum propelling force through magnetization saturation of the MNP. As previously demonstrated by our group, such technique was successful at maintaining microcarriers along a planned trajectory in the blood vessels based on tracking information gathered using Magnetic Resonance Imaging (MRI) sequences from artifacts caused by the same MNPs. Besides propulsion and tracking, the same MNPs can be synthesized with characteristics that can allow for the diffusion of therapeutic cargo carried by these MR-navigable carriers through the Blood Brain Barrier (BBB) using localized hyperthermia without compromising the MRN capabilities. In the present study, an external heating apparatus was used to impose a regional heat shock on the skull of a living mouse model. The effect of heat on the permeability of the BBB was assessed using histological observation and tissue staining by Evans blue dye. Results show direct correlation between hyperthermia and BBB leakage as well as its recovery from thermal damage. Therefore, the proposed navigable agents could be suitable for controlled opening of the BBB by hyperthermia and selective brain drug delivery.
  • Diamagnetically Levitated Robots: An Approach to Massively Parallel Robotic Systems with Unusual Motion Properties Authors: Pelrine, Ron; Wong-Foy, Annjoe; McCoy, Brian; Holeman, Dennis; Mahoney, Rich; Myers, Greg; Herson, Jim; Low, Thomas
    Using large numbers of microrobots to build unique macrostructures has long been a vision in both popular and scientific media. This paper describes a new class of machines, DiaMagnetic Micro Manipulator (DM3) systems, for controlling many small robots. The robots are diamagnetically levitated with zero wear and zero hysteresis, and driven using conventional circuits. Unusual motion properties have been reported in testing these systems, including exceptional open loop repeatability of motion (200 nm rms) and relative speeds (37.5 cm/s or 217 body lengths/s) [1]. A system using 130 micro robots as small as 1.7 mm with densities up to 12.5 robots/cm2 has been demonstrated. This paper reports initial data on robot trajectories, and shows that open loop trajectory repeatabilities on the order of 0.8 micrometers rms or better are feasible in a levitated state compared with 15 micrometers rms repeatability in a non-levitated state with surface contact. These results suggest an encouraging path to complex microrobotic systems with broad capabilities.
  • Magnetic Micro Actuator with Neutral Buoyancy and 3D Fabrication of Cell Size Magnetized Structure Authors: Yasui, Masato; Ikeuchi, Masashi; Ikuta, Koji
    We have developed two technologies for 3D magnetic microstructures, with a wide size range between 5&#956;m to 2mm. The first technology enables us to obtain density controlled 3D magnetic microstructures. The size is approximately 500&#956;m. In this scale, controlling density is vital for magnetic micro actuators, because the effect of gravity is strong. To adjust density, we developed the world’s first “density controllable magnetically photocurable (DMPC) polymer.” The DMPC polymer is a mixture of hollow microcapsules (density, 0.03 g/cm<sup>3</sup>), magnetic particles, and photocurable polymer. We can obtain desired relative density between 0.5 to 1.7 by adjusting the concentration of microcapsules. In addition, we succeeded in 3D velocity control of a screw-type magnetic micro actuator with neutral buoyancy in water. The delay time was 32msec. In addition, the actuator possessed 6 DOF. The second technology realized a 5&#956;m magnetic micro actuator, which is a combination of a 3D transparent structure and 2D magnetic structure. Various photocurable polymers can be applied as the 2D structure in this process, although we used magnetically photocurable polymer in this report. Furthermore, we have succeeded in driving a ferromagnetic micro actuator, whose diameter is as small as 1&#956;m. These two fabrication processes will become key technologies in both medical and life sciences field, because they can supply a wide variety of 3D micro structures with small effort.