Estimation of mass and center of gravity of graspless unknown object using gravity equi-effect planes

In many cases of manipulating an object stably and accurately by robot, it is required to know the center of gravity and mass of the object. For the case when the weight or shape of an object is over the grasp capacity of a robot hand, the paper proposes a technique that can estimate the center of gravity and mass of the graspless and shape-unknown object. A plane called gravity equi-effect plane is first defined, which contains the center of gravity and a contact line where the object is in line-contact with an environment. If three or over three orientation-different gravity equi-effect planes of an object are obtained, the center of gravity of the object can be estimated by the intersect point of the planes. In order to estimate the gravity equi-effect plane, tip operation by a robot finger, which tips the object repeatedly, is proposed. Then an algorithm to estimate the gravity equi-effect plane and an algorithm to estimate the mass and center of gravity of the object are addressed by using the fingertip position and force information measured from tip operations.