Friction drive systems are adopted for many robots of spherical locomotion type. Such systems have problems, including traversing uneven surfaces, slipping of the roller, and dust between the sphere and the roller. Despite of the disadvantages, these systems attract attention because of the possibility of stepped climbing and omnidirectional locomotion. In the future, it is anticipated that the mechanism using the sphere are developed. When the kinematics with respect to multiple rotational axes in arbitrary contacted on the sphere is clarified, the mechanism may be widely used. In the paper, a general theorem for kinematics is discussed including the number of rollers driving the sphere, the type of roller (constraint or unconstraint), and the contact points of the rollers on the sphere and the roller axes direction. To verify the validity of the kinematics model a locomotion model of the ball dribbling mechanism with the two rollers is presented as a special example by carrying out the experimental demonstration using the device robot.
This paper presents a novel measurement method for caging quality based on static analysis of robotic grasping and manipulation. Caging is a geometrical constraint of objects in which those captured by surrounding robots are restricted to move in the bounded space. The object constraint with some margin is a promising tool to allow uncertainties appearing in object perception and robot control. Because of limitation of robot configuration, complete caging that the object never escape from is, however, not accomplished sometimes, and the target object is partially caged. As for such partial caging, the quality of geometrical constraint has not been sufficiently evaluated. In this paper, we propose an evaluation index of the quality based on the robustness of grasping and manipulation in order to deal with both caging and mechanical constraint simultaneously. Some numerical results are presented to validate our proposed procedure of evaluation.