This paper presents a miniature haptic actuator based on MR fluids, which is designed to convey realistic haptic sensations to users in small electronic devices. The proposed MR actuator can create various kinaesthetic sensations. The haptic sensation, which is generated in the form of resistive force, should vary according to the stroke of the actuator (or the pressed depth of the plunger). Thus, a sensing method for gauging the pressed depth should be integrated into the proposed actuator for demonstrating its real-world haptic application. To determine the pressed depth of the MR actuator, this study proposes an impedance sensing mechanism. The proposed sensing method measures the impedance change of the solenoid coil embedded in the actuator in the form of voltages to estimate the pressed depth. Using a prototype actuator, the sensing performance of the proposed sensing method, was evaluated. The results show that the sensitivity of the proposed impedance sensing method is sufficient to regulate the output resistive force over a small stroke range of the actuator.

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