Free hand haptic interfaces based on magnetorheological fluids

This paper is concerned with exploring the possibility of using Magneto-Rheological Fluids (MRF) as haptic, interface. MRF are special materials capable of changing their theological behaviour with an external magnetic field. This property suggested us to use MRF to mimic virtual objects whose compliance can be gradually modulated. Several architectures of prototypes have been envisaged. The general scheme of both prototypes refers to a Haptic Black Box (HBB) concept, intended as a box where the operator can poke his/her bare hand, and interact with the virtual object by freely moving the hand without mechanical constraints. In this way sensory receptors on the whole operator's hand would be excited, rather than restricting to just one or few fingertips or phalanges. Here we describe the technical evolution from an earlier prototype (HBB-I) which allowed to create only planar virtual objects to a new architecture (HBB-II) capable of reproducing 3D virtual objects. A comparative description of the two devices in terms of technical details and performance is reported, using simulations based on finite element methods. A set of qualitative psychophysical experiments is also reported to assess the improved performance of HBB-II in discriminating softness and shape of virtual objects.