Design of a Twisted String Actuated Haptic Thimble for Cutaneous Force Feedback

Sense of touch in virtual reality and teleoperation can be delivered by compact and wearable devices, worn at users’ hands. Fingertip haptic devices in the shape of actuated thimbles can render highly informative cutaneous feedback. Design of wearable fingertip haptic devices is often a compromise between conflicting features: lightness and compactness, and richness and intensity of the haptic feedback. Mechanical transmissions with reduction can increase output force of micro-sized motors, yet introducing noise and vibrations which degrade quality of the rendered signals. In this work we experimented a different method to actuate fingertip haptic device, based on twisted string actuators: a reduction stage is obtained by twisting a tendon transmission with a rotary motor. It constitutes a lightweight and noiseless reduction that can achieve high output force in a compact mechanism. In the work we present design and implementation of the device, followed by experimental characterization of its performance in terms of frequency response and output force capabilities.