A haptic interface mediates positions and forces between a human operator and a telepresent or virtual environment. Consequently, it must be able to sense the poses of the human hands and exert forces on the hands at the same time. In numerous application domains, e.g. telepresent maintenance work or virtual shopping, the user is expected to walk around in the target environment. Hence, the desired workspace is far larger than the reach of the human arm. The workspace covered by typical haptic interfaces, however, is even much smaller than the full reach of the human arm. In order to enable haptic interaction in spatially unlimited environments, an alternative approach must be chosen.

To this end, two haptic displays have been mounted on a mobile base. When the position of the mobile base is controlled in such a way that the end-effectors of both haptic displays are kept far from the limits of their respective workspaces, the operator can move around freely while the mobile base actively follows his motions. The typical scheme of operation is illustrated in the figure on the left: the hands of the human operator are coupled to the end-effectors of the haptic displays which are used to track positions and exert forces. The combined position data from haptic displays and mobile base are sent to a virtual avatar or mobile teleoperator which implements the given movements in the target environment.