The development of variably compliant haptic systems using magnetorheological fluids

In this study the authors develop haptic systems for telerobotic surgery. In order to model the full range of tactile force exhibited from an MR damper a microstructural, kinetic theory-based model of Magnetorheological (MR) fluids has been developed. Microscale constitutive equations relating flow, stress, and particle orientation are produced. The model developed is fully vectorial and relationships between the stress tensor and the applied magnetic field vector are fully exploited. The higher accuracy of the model in this regard gives better force representations of highly compliant objects. This model is then applied in force feedback control of single degree of freedom (SDOF) and two degrees of freedom (2DOF) systems. Carbonyl iron powders with different particle sizes mixed with silicone oils with different viscosities are used to make several sample MR fluids. These MR fluid samples are then used in three different designed MR dampers. A State feedback control algorithm is employed to control a SDOF system and tracking a 2-D profile path using a special innovative MR force feedback joystick. The results indicate that the MR based force feedback dampers can be used as effective haptic devices. The systems designed and constructed in this paper can be extended to a three degree of freedom force feedback system appropriate for telerobotic surgery.