Presentation of Underwater Sensation by Drag in Knee Motion with a Lower Limb Exoskeleton Using MR Fluid Brakes

In recent years, force feedback devices have been developed to improve the reality of VR experiences. However, a majority of force feedback devices target the upper limbs. Force feedback to the lower limbs will enable a VR experience that cannot be achieved by force feedback to the upper limbs alone. In this study, an exoskeletal lower limb force-feedback device was developed to improve the sense of reality in a Virtual Reality (VR) space. This device has Magnetorheological (MR) fluid brakes placed at the joints and can present frictional and viscous force through torque control. We designed a drag model that simplifies the force generated in reality as the force presented when the knee is operated in water. Then, the sensation of motion when the knee is flexed and extended in water was evaluated from the viewpoints of reality and drag force. The experimental results showed that the force presentation using the MR fluid brake proportional to the velocity gave a sense of reality of approximately 50%.