This paper presents the force-feedback performance of an active type of haptic device featuring an electrorheological ( ER) fluid via a sliding mode controller (SMC), which is very robust to external disturbances and parameter uncertainties. In order to generate a 2-degrees-of-freedom (2-DOF) active force, a spherical ER joint is designed based on the mathematical torque model. The ER joint is then manufactured by adopting two bi-directional clutch actuators and the spherical geometry of the electrode, and its field-dependent generating force is experimentally evaluated. Subsequently, the 2-DOF force display is manufactured by integrating the ER joint with AC motors. The force response of the manufactured haptic device is experimentally evaluated, and expressed by a second-order dynamic equation. In order to achieve the desired force trajectories, the SMC is formulated and experimentally realized by imposing an Euler angle relationship. Tracking control performances for various force trajectories are presented in the time domain, and their tracking errors are evaluated.
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