Object Handing with a Robotic Hand Equipped with Optical Three-Axis Tactile Sensors

M. Ohka, J. Takata, H. Kobayashi, H. Yussof, and Y. Mitsuya (Japan)

Keywords

Robotic Hand, Tactile Sensor, Threeaxis, Optical Waveguide, Grasping, Slippage.

Abstract

In object handing, a robot should decide proper grasping force on the basis of the hardness of an object and the degree of surface slipperiness, which are estimated by three-axis tactile sensors mounted on its fingers. In the present paper, we produce a tactile sensor based on the principle of an optical waveguide-type tactile sensor, which is composed of an acrylic hemispherical dome, a light source, an array of rubber sensing elements, and a CCD camera. The sensing element of silicone rubber comprises one columnar feeler and eight conical feelers. The contact areas of the conical feelers, which maintain contact with the acrylic dome, detect the three-axis force applied to the tip of the sensing element. Normal and shearing forces are then calculated from integration and centroid displacement of the gray-scale value derived from the conical feeler’s contacts. Two three-axis tactile sensors are mounted on the fingers of a three-joint articulated two-finger robotic hand. In the grasping tests, the robotic hand measures the hardness of an object to decide the proper grasping force before trying to move it. The robotic hand can move not only a hard aluminum block but also an easily crushed paper box.

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