A Free-Hand Haptic Interface Based on Magnetorheological Fluids
In this work we investigate the possibility of mimicking haptic perception by using rheological materials. An analysis of the rheological behaviour of some ”smart fluids”, such as Electro-rheological Fluids (ERFs) and Magneto-rheological Fluids (MRFs), is
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mmary. In this work we investigate the possibility of mimicking haptic perception by using rheological materials. An analysis of the rheological behaviour of some ”smart fluids”, such as Electro-rheological Fluids (ERFs) and Magneto-rheological Fluids (MRFs), is provided to design new haptic interfaces capable of reproducing shape and compliance of some virtual objects. Some theoretical design considerations are discussed and supported by magnetic simulations implemented by means of a numerical code. Several prototypes were designed and realized through a progressive enhancement of performance up to a final 3D immersive device. Furthermore, to assess performance a set of psychophysical tests was carried out and experimental results in terms of softness and shape recognition are reported.
7.1 Introduction The present work proposes a viable solution for improving haptic perception in virtual environments, providing a haptic display capable of mimicking the softness and shape of some viscoelastic materials, such as biological tissues. Our goal was to investigate the possibility of using the smart fluids for mimicking the compliance, damping and creep (in other terms, the rheology) of some materials in order to realize haptic displays. The main innovation concerns the direct interaction with the fluid without rigid linkages and mechanical constraints. This approach is mainly motivated by the fact that the viscoelasticity of some materials and, i.e. biological tissues, is comparable to the that of most commercial rheological fluids. One of the most pressing limitations of commercial haptic devices is the operator’s loss of tactile sensibility during manipulation tasks due to the transmission mechanism used during the interaction. The operator may manipulate the virtual objects and by only using long tools, observing actions and movements on a monitor displaying the virtual environment (VE) . He can neither touch nor see the virtual object directly. Diminished tactile sensibility causes a loss of discrimination capability, particularly with regard to the softness and viscoelasticity of the object. A. Bicchi et al.(Eds.): The Sense of Touch and Its Rendering, STAR 45, pp. 155–178, 2008. c Springer-Verlag Berlin Heidelberg 2008 springerlink.com
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Fig. 7.1. Internal configuration of the ERF/MRF in the absence of the electric/magnetic field (left), in intermediate configuration (middle) and with a high electric/magnetic field applied (right)
In such a way the use of these rheological fluids as direct haptic displays could be a viable solution in important applications such as surgical training in Minimally Invasive Surgery (MIS) and Open Surgery (OS) . Indeed, in MIS the MRF could be used as haptic interface to be integrated in the surgical tool in order to provide the surgeon with the lost tactile perception. In OS the MRF could be used, instead, to virtually create the internal organs of the abdominal cavity allowing the trainee surgeon to learn their compliance from palpating them. In MIS, a small-size
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