This study presents force feedback control performance of a spherical haptic device featuring an electrorheological (ER) fluid that can be used for minimally invasive surgery (MIS). As a first step, a spherical ER joint composed of rotational and stationary electrodes is designed and optimized based on mathematical torque modeling. The active force produced in MIS is generally small, even though the passive force is large. In order to meet this agreement, both clutch and brake mechanism are adopted for the ER joint. In this operation, the active (small) force feedback by the rotational electrodes and/or semi-active (large) force feedback are achieved by the stationary electrode. Subsequently, the master device is manufactured by integration of the spherical ER joint with AC motor. In order to achieve desired force trajectories, a sliding mode controller, which is robust to uncertainty, is formulated by considering mechanical friction and hysteretic behavior of the ER fluid as uncertainty. The controller is then experimentally realized. Tracking control performances for various force trajectories are presented in time domain.
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