A Dual-Modal Vision-Based Tactile Sensor for Robotic Hand Grasping

Humans' fingertips can perceive not only the magnitude and the direction of force but also the texture of object. When we grasp an object, the surface texture sensing of the fingertip helps us recognize the object and the force feeling that is parallel to the skin helps us grasp stably. Focusing on these points, we have developed a dual-modal vision-based tactile sensor that can measure the texture of object and a distribution of force vectors. The tactile sensor consists of a transparent elastomer, a camera, a piece of transparent acrylic board, LEDs and supporting structures. A reflective membrane and markers array are on the surface of the elastomer. An applied force on the elastic body results in movements of the markers, which are acquired by the CCD camera. In addition, the shape and texture of the object's contact surface can be reflected by the membrane deformations. The distribution of force vectors is determined by the BP neural network. The local binary pattern algorithm using captured images calculates the texture information. This paper reports experimental evaluation results concerning accuracy of determination of magnitude, direction of force, and texture recognition rate.