Abstract: This paper presents the design concept, models, and open-loop control of a particular form of a variable-reluctance spherical motor (VRSM), referred here as a spherical wheel motor (SWM). Unlike existing spherical motors where design focuses have been on controlling the three degrees of freedom (DOF) angular displacements, the SWM offers a means to control the orientation of a continuously rotating shaft in an open-loop (OL) fashion. We provide a formula for deriving different switching sequences (full step and fractional step) for a specified current magnitude and pole configurations. The concept feasibility of an OL controlled SWM has been experimentally demonstrated on a prototype that has 8 rotor permanent-magnet (PM) pole-pairs and 10 stator electromagnet (EM) pole-pairs.

Models quasi-statically the force acting on an object by a rotating flexible finger. As compared to fingers with multiple active joints, flexible fingers have many potential advantages; specifically, they are lightweight and have no relative individual moving parts in each of the fingers. Their ability to accommodate a limited range of varying sizes, shapes, and the natural reactions of some objects (without the need of a feedback mechanism such as a visual servo) makes a system using flexible fingers an attractive candidate for use as a grasper in a high-speed production setting. The advantages of flexible fingers are seldom exploited for grasping, however, because of complicated analyses involved in their design. The paper offers two methods to determine contact points/forces. The first analytical model, based on the Frisch-Fay (1962) flexible bar theory, provides an approximate closed-form solution for determining the contact points and forces. The second method using FEM predicts the stress distribution around the contact area. Both methods of predicting the contact forces have been verified experimentally. The effects of parameter variations are presented. Our results demonstrate that the model could be used as a practical means to measure the contact force between the finger and the live object.