Abstract
This paper shows that secure pinching under the gravity effect can be realized by a pair of robot fingers with hemispherical ends using a coordinated sensory-feedback signal constructed without any information of an object (e.g., center of mass, mass, length, object angle) . The proposed control signals which can be easily calculated from only encoder data of the finger angles and the finger physical parameters are adaptable to rigid objects with parallel or non-parallel flat surfaces. Numerical simulations and experimental results show that the closed-loop finger-object system finally falls into some stable state satisfying the force/torque balance, that is, into a force/torque equilibrium point. In other words, the results show that stable “blind grasping” under the situation of closing eyes and neither using any tactile sensor nor force-sensing can be actualized even by a pair of robot fingers like human pinching an object by means of the thumb and index finger, provided that preshaping of finger postures is fulfilled adequately.
