FingerTac is a novel concept for a wearable augmented haptic thimble. It makes use of the limited spatial discrimination capabilities of vibrotactile stimuli at the skin and generates tactile feedback perceived at the bottom center of a fingertip by applying simultaneous vibrations at both sides of the finger. Since the bottom of the finger is thus kept free of obstruction, the device is well promising for augmented haptic applications, where real world interactions need to be enriched or amalgamated with virtual tactile feedback. To minimize its lateral dimension, the vibration actuators are placed on top of the device, and mechanical links transmit the vibrations to the skin. Two evaluation studies with N=10 participants investigate (i) the loss of vibration intensity through these mechanical links, and (ii) the effect of lateral displacement between stimulus and induced vibration. The results of both studies support the introduced concept of the FingerTac.

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Pfaffian (velocity) constraints are encountered commonly in mechanical systems. In many cases, the measurements for feedback control are obtained from an exteroceptive sensor system, which is not only of low rate, but also suffers from physical discontinuities. This negatively affects controller performance and places severe limitations on the choice of control parameters. To this end, a novel framework comprised of a rigid Body Observer (BObs) and a pose regulator is proposed. During the intersampling periods, the observer propagates the state based on an internal model to provide continuous estimates, which are exploited by the pose regulator to stabilize equilibria. We prove uniform asymptotic stability for the closed loop. Furthermore, we validate the proposed framework through simulation and also the BObs experimentally.

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