Tham khảo tài liệu 'sensors, focus on tactile, force and stress sensors 2011 part 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 141 Measurement Principles of Optical Three-Axis Tactile Sensor and its Application to Robotic Fingers System 8. Conclusion In this research we developed the original hemispherical shaped optical three-axis tactile sensor system to mount on robotic fingers. The tactile sensor is capable of acquiring normal and shearing forces which are the most important sensing elements in object manipulation tasks. 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. 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. In this chapter we have presented force detection and measurement principles of the tactile sensor for normal and shearing forces. The normal force is calculated based on brightness changes of visual image taken by CCD camera. To define the applied force we measure the integrated gray-scale value of the bright area. Meanwhile shearing force is calculated by measuring centroid point displacement of the bright area retrieved by the CCD camera. 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 we conducted calculations to define coordinate transformation of the sensing elements on the sensor s hemispherical shape dome. The optical three-axis tactile sensors are mounted on fingertips of two robotic fingers
