Control of a desktop mobile haptic interface

Most haptic devices share two main limits: they are grounded and they have limited workspace. A possible solution is to create haptic interfaces by combining mobile robots and standard grounded force-feedback devices, the so called Mobile Haptic Interfaces (MHIs). However, MHIs are characterized by dynamical limitations due to performance of the employed devices. This paper focuses on basic design issues and presents a novel (prototype) Mobile Haptics Platform that employs the coordination of numerically controlled wheel torques to render forces to a user handle placed on the top of the device. The interface, consisting in a small omni-directional robot, is link-less, fully portable and it has been designed to support home-rehabilitation exercises. In the present paper we shall review relevant choices concerning the functional aspects and the control design. In particular a specific embedded sensor fusion was implemented to allow the device to move on a desk without drifting. The sensor fusion algorithm has been optimized to provide users with a quality force feedback while ensuring accurate position tracking. The two requirements are in contrast each other and a specific variant of the Extended Kalman Filter (EKF) was required to allow the device working.