Optical Three-axis Tactile Sensor for Robotic Fingers

Tactile sensors capable of sensing normal and shearing force produced on a robotic finger and an object are useful for fitting a dextrose hand that can be applied to tasks that require human-like handling. Examples include such manufacturing tasks as assembly, disassembly, inspection, and materials handing. Especially in the case of humanoid robots, grasping slippery or flexible objects is required in living environments for human beings in contrast to industrial robots that handle standardized objects in controlled environments. Since the three-axis tactile sensor is effective in such cases, its importance will increase with improvements in humanoid robots. A hemispherical tactile sensor is developed for general-purpose use with our three-axis tactile sensor that is mounted on the fingertips of a multi-fingered hand. The present threeaxis tactile sensor is comprised of an acrylic dome, a light source, an optical fiber scope, and a CCD camera. The light emitted from the light source is directed onto the edge of the hemispherical acrylic dome through optical fibers. The sensing elements are concentrically arranged on the acrylic dome. In the following sections, after conventional tactile sensors are summarized to compare the present tactile sensor’s merits and demerits with conventional tactile sensors,’ the principle of the three-axis tactile sensor is described. Then the basic sensing characteristics are examined for evaluating the present tactile sensor. Not only normal and shearing force sensing but also repeatability is examined in a series of experiments. Finally, surface scanning and object manipulation with one finger are shown to verify the applicability of the present tactile sensor to multi-fingered hands.