Jumpei Takata

Sensing Precision of an Optical Three-axis Tactile Sensor for a Robotic Finger

We are developing an optical three-axis tactile sensor capable of acquiring normal and shearing force, with the aim of mounting it on a robotic finger. The tactile sensor is 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 feelers contacts. To evaluate the present tactile sensor, we have conducted a series of experiments using a y-z stage, a rotational stage, and a force gauge, and have found that although the relationship between the integrated gray-scale value and normal force depends on the sensors latitude on the hemispherical surface, it is easy to modify the sensitivity according to the latitude, and that the centroid displacement of the gray-scale value is proportional to the shearing force. When we examined repeatability of the present tactile sensor with 1,000 load-unload cycles, the respective error of the normal and shearing forces was 2 and 5%

Low force control scheme for object hardness distinction in robot manipulation based on tactile sensing

This paper presents an application of a low force interaction method in a control scheme of robot manipulation based on tactile sensing. Our aim is to develop an intelligent control system that can distinguish the hardness of unknown objects so that robotic fingers can effectively explore the objects surface without altering its physical properties or causing damage. Initially we developed a novel optical three-axis tactile sensor system based on an optical waveguide transduction method capable of acquiring normal and shearing forces. The sensors are mounted on the fingertips of the multi-fingered humanoid robot arm. We proposed a new control scheme applying low force interaction to distinguish the hardness of unknown objects in robot manipulation tasks based on tactile sensing. The scheme utilized new control parameters obtained by calibration experiments using hard and soft objects that enable robot fingers to precisely control grasp pressure and define the slippage sensation of the given object. Finally, verification experiments of the proposed control scheme using a humanoid robot arm were conducted whose results revealed that the fingers system managed to recognize the hardness of unknown objects and complied with sudden changes of the objects weight during object manipulation tasks.

Object exploration and manipulation using a robotic finger equipped with an optical three-axis tactile sensor

To evaluate our three-axis tactile sensor developed in preceding papers, a tactile sensor is mounted on a robotic finger with 3-degrees of freedom. We develop a dual computer system that possesses two computers to enhance processing speed: one is for tactile information processing and the other controls the robotic finger; these computers are connected to a local area network. Three kinds of experiments are performed to evaluate the robotic fingers basic abilities required for dexterous hands. First, the robotic hand touches and scans flat specimens to evaluate their surface condition. Second, it detects objects with parallelepiped and cylindrical contours. Finally, it manipulates a parallelepiped object put on a table by sliding it. Since the present robotic hand performed the above three tasks, we conclude that it is applicable to the dexterous hand in subsequent studies.

Development of an Optical Three-Axis Tactile Sensor for Object Handing Tasks in Humanoid Robot Navigation System

Summary. Autonomous navigation in walking robots requires that three main tasks be solved: self-localization, obstacle avoidance, and object handling. This report presents a development and application of an optical three-axis tactile sensor mounted on a robotic finger to perform object handling in a humanoid robot navigation system. Previously in this research, we proposed a basic humanoid robot navigation system called the groping locomotion method for a 21-dof humanoid robot, which is capable of defining self-localisation and obstacle avoidance. Recently, with the aim to determining physical properties and events through contact during object handling, we have been developing a novel optical three-axis tactile sensor capable of acquiring normal and shearing force. The tactile sensor system is combined with 3-dof robot finger system where the tactile sensor in mounted on the fingertip. Experiments were conducted using soft, hard, and spherical objects to evaluate the sensors performance. Experimental results reveal that the proposed optical three-axis tactile sensor system is capable of recognizing contact events and has the potential for application to humanoid robot hands for object handling purposes.

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.

Measurement Principles of Optical Three-Axis Tactile Sensor and its Application to Robotic Fingers System

A tactile sensor is a device that can measure a given property of an object or contact event through physical contact between the sensor and the object. Traditionally, tactile sensors have been developed using measurements of strain produced in sensing materials that are detected using physical quantities such as electric resistance and capacity, magnetic intensity, voltage and light intensity (Nicholls, 1990). Research on tactile sensor is basically motivated by the tactile sensing system of the human skin. In humans, the skin’s structure provides a mechanism to simultaneously sense static and dynamic pressure with extremely high accuracy. Meanwhile in robotics, several tactile sensing principles are commonly used nowadays, such as capacitive, piezoelectrical, inductive, piezoresistive, and optoelectrical sensors (Schmidt et al., 2006, Lee & Nicholls, 1999). In our research lab, with the purpose to establish object manipulation ability in robotic fingers, we developed a hemispherical shaped optical three-axis tactile sensor capable of acquiring normal and shearing forces to mount on the fingertips of robot fingers. This tactile sensor uses an optical waveguide transduction method and applies image processing techniques. Such a sensing principle is expected to provide better sensing accuracy to realize contact phenomena by acquiring the three axial directions of the forces, so that normal and shearing forces can be measured simultaneously. This tactile sensor is designed in a hemispherical dome shape that consists of an array of sensing elements. This shape is to mimics the structure of human fingertips for easy compliance with various shapes of objects. For miniaturization of the tactile sensor, measurement devices are placed outside the sensor. The small size of the sensor makes it easy for installation at robotic fingers. The optical three-axis tactile sensor developed in this research is designed in hemispherical shape, and the sensing elements are distributed in 41-sub region. Due to this structure, the acquired images by CCD camera, except for sensing element at the sensor tip area, are not the actual image of contact pressure at the sensing elements. Therefore, to compensate with the sensor structure, it is necessary to conduct coordinate transformation calculations for each sensing element except for the element at the sensor tip area. In this chapter, we

Application of Contact-Based Sensors for Self-Localization and Object Recognition in Humanoid Robot Navigation Tasks

This paper presents the application of a six-axis force sensor and a novel optical three-axis tactile sensor to humanoid robot navigation system which is based on contact interaction towards supporting visual-based navigation. The force sensors are mounted on humanoid robot arms to perform grasping in self-localization task to define the robots position and orientation. The grasping results guided the robot locomotion and avoid it from collision. Meanwhile the optical three-axis tactile sensors are mounted on cooperative two-finger system for object handling tasks. The tactile sensor is capable of acquiring normal force and shearing force. Experiment with hard and soft objects are performed which results revealed good performance of the integrated robotic fingers and tactile sensor system to recognize and grip the objects. The presented control algorithms for both sensors are capable of preventing the probability of damage to the sensors and objects during robust grasping and object handling tasks.