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.