It is believed that the use of haptic sensors to measure the magnitude, direction, and distribution of a force will enable a robotic hand to perform dexterous operations. Therefore, we develop a new type of finger-shaped haptic sensor using GelForce technology. GelForce is a vision-based sensor that can be used to measure the distribution of force vectors, or surface traction fields. The simple structure of the GelForce enables us to develop a compact finger-shaped GelForce for the robotic hand. GelForce that is developed on the basis of an elastic theory can be used to calculate surface traction fields using a conversion equation. However, this conversion equation cannot be analytically solved when the elastic body of the sensor has a complicated shape such as the shape of a finger. Therefore, we propose an observational method and construct a prototype of the finger-shaped GelForce. By using this prototype, we evaluate the basic performance of the finger-shaped GelForce. Then, we conduct a field test by performing grasping operations using a robotic hand. The results of this test show that using the observational method, the finger-shaped GelForce can be successfully used in a robotic hand.
Abstract-Humans can perceive not only the magnitude but also the direction of force applied on the fingertip. When we grasp an object, the weight of it is felt through force that is parallel to the skin of the fingertip, which is how the object can be grasped without slipping. Focusing on this point, we have developed a tactile sensor that can measure a distribution of force vectors. The measurement method is as follows. The tactile sensor consists of a transparent elastic body, blue and red markers inside the elastic body, and a color CCD camera. An applied force on the elastic body results in movements of the markers, which are acquired by the CCD camera. The distribution of force vectors is calculated using this information. This paper reports experimental evaluation results concerning accuracy of determining position of markers, determination of magnitude and direction of force, spatial resolution, and calculation timing.
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